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The next annual meeting, hosted by CERN, will take place from 21 - 25 August 2017 in Genève at two different locations. Starting at CERN on 21st with internal meetings of some of the participating societies, the 22nd will be dedicated to plenary and invited talks and more (see below). We will then move to the Centre International de Conférences de Genève (CICG) on 23 - 25 August where further plenary talks and all topical sessions will take place. The meeting is organised - as every two years - as a joint meeting with the Austrian Physical Society ÖPG and the Swiss Society for Astrophysics and Astronomy SSAA. The Swiss Institute of Particle Physics (CHIPP) will participate additionally to their usual 2-year rhythm. We also welcome for the first time the NCCR MARVEL (Computational Design and Discovery of Novel Materials).
Extended Abstract Submission Deadline: 30 May 2017
Please note that if you do not already have a CERN indico account, you must create a CERN lightweight account before submitting an abstract. Procedure here:
https://account.cern.ch/account/Externals/RegisterAccount.aspx
Registration Deadline extended until 8 August 2017, 18:00h. Don't forget to register !
Internal meetings of SPS and ÖPG Committees and the respective General Assemblies
Only available on registration through the Conference Registration form. Choose from the available visits there.
Only available on registration through the Conference Registration form. Choose from the available visits there.
Internal meetings of SPS and ÖPG Committees and the respective General Assemblies
Only available on registration through the Conference Registration form. Choose from the available visits there.
The presidents of SPS and ÖPG and the CERN DG welcome all participants of the Joint Annual Meeting 2017.
Following a short outline of the history and composition of CERN, emphasis will be given on the core mission of CERN in the fields of accelerators, detectors and computing.
Educational aspects, innovation drivers and technological challenges are described with respect to present and future projects like FCC and CLIC.
CERN the European Laboratory for Particle Physics provides the infrastructure and in particular accelerators for a large variety of physics experiments for users from Europe and elsewhere. These experiments range from low energy atomic physics to particle physics at the highest available energies. The flagship project at CERN is the Large Hadron Collider and the experiments attached to it. At a centre of mass energy of presently 13 TeV the experiments at the LHC explore a new energy regime. The physics studies cover all known particles of the Standard Model of Particle Physics including the Higgs Boson and the search for new particles or deviations from the Standard Model theoretical predictions. Using the accelerator complex at CERN many more experiments are conducted: high energy fix-target experiments for precision studies, low energy experiments using antiprotons and anti-Hydrogen, atomic physics and nuclear physics experiments using radioactive isotopes, and many more. CERN is also the place for the European neutrino physics community to prepare contributions to the neutrino physics programme outside Europe.
This presentation will give an overview of the experimental physics programme at CERN.
Accelerators are developed and built to help advance the limits of our knowledge across a wide spectrum of fields. The high energy and precision frontiers in particle physics, synchrotron light sources with high intensity, coherence and extremely short pulses, intense neutron and muon beams as well as proton beams for medical applications, are some examples of recent advances that have taken place at the two world class accelerator laboratories CERN and PSI. The presentation will illustrate the on-going development of accelerator concepts beyond the existing technology including the high-field superconducting magnets, high gradient and compact accelerators. The current analytic capabilities of the present accelerator-based platform for experimental science are being transformed to a facility for industrial problem solving. The advanced manufacturing with analytics platforms will in turn play a crucial role in the development of advanced accelerator components that will form the basis for future accelerator-driven infrastructure.
The discovery in 2015 by the LIGO collaboration of the first gravitational wave signal from coalescing black holes and the superb performance of the LISA Pathfinder satellite opened a new window to explore the Universe.
I will discuss these exciting developments and also the future of the field, in particular the space-based mission LISA to detect gravitational waves from space. I will give an overview of the main scientific goals of LISA. In particular, it will be able to study in great detail mergers of supermassive black holes, which are present in the galactic centers. It will thus allow to test general relativity in the strong gravity regime to high accuracy.
Internal meetings of SPS and ÖPG Committees and the respective General Assemblies
Internal meetings of SPS and ÖPG Committees and the respective General Assemblies
CHEOPS (Characterising ExOPlanet Satellite) is the first exoplanet mission dedicated to the search for transits of exoplanets by means of ultrahigh precision photometry of bright stars already known to host planets. CHEOPS is also the first S-class mission in ESA’s Cosmic Vision 2015-2025 programme and is scheduled to launch end of 2018. The mission is a partnership between Switzerland and ESA’s science programme with important contributions from Austria, Belgium, France, Germany, Hungary, Italy, Portugal, Spain, Sweden, and the United Kingdom. In this presentation I will give an overview of the scientific goals of the mission and discuss some of the challenges encountered.
The discovery of the Higgs boson has opened the door to a new era in particle physics. This particle is a conundrum. Unlike any previously discovered, it raises more questions than it answers. What fundamental laws operate at the smallest distance scales? Where did the matter we are made of come from and, while we’re on that topic, what is the dark matter? All evidence suggests the Higgs is, at the least, a co-conspirator in these mysteries.
In the continued attempt to search for answers, theoretical physicists are increasingly looking towards cosmology, where fundamental questions may be linked to the physics of the most ginormous proportions. In this talk I will discuss current approaches to these puzzles and explain how the physics of the cosmos is shaping our understanding of the results from the worlds most powerful microscope: The Large Hadron Collider (LHC). This is a two way street, and I will explain how measurements from particle colliders have consequences for our understanding of the very earliest Universe, and its ultimate fate.
Arguably, the only really useful single photon source in quantum technology is a source of close-to-perfect single photons. The demands are stringent in terms of purity (the level of anti-bunching), coherence (the level of indistinguishability) and brightness (the efficiency of the entire device). Such a source would find applications in device-independent quantum cryptography. The quantum repeater requires in addition a stationary bit at each node, for instance a coherent spin. Ideally therefore, a system is required with a coherent spin and efficient spin-photon interface.
Implementing these ideas in the solid-state is appealing as nano-technology can potentially add a lot of device functionality. However, a solid-state environment is a source of noise, phonons in the lattice, charge noise from fluctuating charges in the solid and spin noise from the fluctuating nuclear spins of the host atoms. Also, a solid-state emitter may emit not just a photon (the zero-phonon-line) but also a photon together with a phonon.
Reported here is progress on two prominent solid-state emitters, a semiconductor quantum dot [1] and the NV colour centre in diamond. The two emitters have complementary strengths and weaknesses. A semiconductor quantum dot is a source of high quality single photons but single spins dephase rather rapidly. Conversely, the NV centre hosts a highly coherent spin but the photons are of low quality.
In the case of quantum dots, the noise in high quality material is very low [2] and in the best case (resonant excitation at low temperature), transform-limited linewidths have been achieved [3]. A micro-cavity is under development with the goal of increasing the brightness [4]. A quantum dot electron spin dephases rapidly on account of the spin noise in the nuclei. A hole spin is a viable alternative and dephases much less rapidly than an electron spin in the presence of unprepared nuclear spins [5].
In principle, a resonant micro-cavity confers multiple benefits to the NV centre photons: faster recombination, preferential emission into the micro-cavity mode, and, crucially, an increase in the zero-phonon-line fraction. In practice, it has been difficult to secure these advantages, largely because nano-fabrication of diamond is very challenging. However, an increase in the zero-phonon-line fraction from 3% to close to 50% has now been achieved by embedding ultra-pure diamond membranes in a micro-cavity [6].
[1] R. J. Warburton, Nature Materials 12, 483 (2013)
[2] A. V. Kuhlmann et al., Nature Physics 9, 570 (2013)
[3] A. V. Kuhlmann et al., Nature Communications 6, 824 (2015)
[4] L. Greuter et al., Physical Review B 92, 045302 (2015)
[5] J. Prechtel et al., Nature Materials 15, 981 (2016)
[6] D. Riedel et al., arXiv:1703.00815 (2017)
Light can hold, move and measure micro- and nano particle without touching. Thus, optical tweezers have emerged as an exciting technology which enables not only to confine microscopic particles near the focal spot of a tightly focused laser beam, but also to measure forces at the nanoscale or quantify biomechanics of single cells.
Complex tailored light field based on holographic principles allow extending this application range, making holographic optical tweezers to an extraordinary metrology tool for analysis in biomechanics and biophotonics. This way, three dimensional configurations of micro- and nano particles can be generated in parallel and dynamically modified, creating spatially selective sensors that can inspect cells in vivo in a noncontact, sterile way.
Particles as well as microsurgery tools created by soft laser lithography can also be introduced into cells to study cellular mechanics in a spatially resolved way, thus paving the way to decipher origins of cell migration and morphogenesis ,or analyze infections and inflammation.
In this presentation, we discuss how the combination of our techniques provides a versatile toolbox for optical micromanipulation of almost all kinds of micro particles. We specifically present examples of trapping cells in in vascular systems or in organisms in vivo, and of quantifying their biomechanical features.
Manufacturing and optical design technologies have placed considerable limitations on the realization of highly useful reflective optical systems. However, recent advances in manufacturing technology combined with novel optical designs that take advantage of the total technology potential has greatly increased the capability of reflective optical systems. This has led to the creation of new reflective optical systems for various applications which afford compactness, lightweight, rigidity and athermal features as well as low cost. Several examples of such systems which cover single and multiple wavebands spanning soft X-ray and near EUV wavelengths to visible and far infrared wavelengths will be described.
Light-matter interaction in condensed matter is a fascinating research field, at the intersection between physics and technology. Semiconductor quantum structures have played a very important role in this field and are a clear example of how fundamental physics and technology mutually enrich each other. The advent of epitaxial growth (bottom-up) has allowed the realization of 2-dimensional structures at the nanometer level, opening a wealth of new exploration in fundamental physics and producing highly performing technologies, such information and communication. The continuous progresses of these technologies have stretched the limit of fabrication processing (top-down) also to nanometer precision and today top-down and bottom-up techniques converge at the nanometer world. This allows the conception and realization of structures confining electrons and photons in the 3 dimensions of the space, which are ideal for engineering and exploring new quantum effects. Our interventions at the nanometer level can transform material global properties or produce individual quantum structures sensitive to single photons or single electrons.
This is the context of my research for the past 20 years, which I will briefly review during this presentation. Indeed, most of my carrier has been devoted to investigations of light-matter interaction in low-dimensional structures to conceive and realise high performance light emitters and detectors. I will begin by presenting our work on quantum cascade lasers, subsequently I will show how we got interested on ultra-strong light matter interaction in order to introduce new characteristic times in optoelectronic devices and I will conclude with our research on superradiance.
Recently we have predicted a new quasiparticle - the angulon - which is formed when a quantum impurity (such as a molecule, atom, or electron) exchanges its orbital angular momentum with a many-particle environment (such as lattice phonons or a superfluid) [1,2].
Soon thereafter we obtained strong evidence that angulons do exist, and are, in fact, created in experiments on molecules trapped inside superfluid helium nanodroplets [3]. The angulon theory thereby provided a simple explanation for experimental data accumulated during last two decades. Moreover, casting the many-particle problem in terms of angulons amounts to a drastic simplification and allows to tackle previously intractable problems [4].
In this talk we will introduce the angulon concept and discuss novel physical phenomena [1,5] arising from the angular momentum exchange in quantum many-particle systems. We will describe the applications of angulons to modern experiments on controllable molecules and ultracold quantum gases.
[1] R. Schmidt, M. Lemeshko, Phys. Rev. Lett. 114, 203001 (2015)
[2] R. Schmidt, M. Lemeshko, Phys. Rev. X 6, 011012 (2016)
[3] M. Lemeshko, Phys. Rev. Lett., 118, 095301 (2017); Viewpoint: Physics 10, 20 (2017)
[4] B. Shepperson, A. A. Sondergaard, L. Christiansen, J. Kaczmarczyk, R. E. Zillich, M. Lemeshko, H. Stapelfeldt, Phys. Rev. Lett. 118, 203203 (2017)
[5] E. Yakaboylu, M. Lemeshko, Phys. Rev. Lett., 118, 085302 (2017)
The Poster Session is held on Wed and Thu. All posters are to be presented on both days. However, due to technical reasons, the contributions are only listed in the timetable of Wed.
The photodissociation cross section of different CsnIn-1+ (n < 8) clusters is measured in a commercial Bruker 9.4 T ICR, where the fragmentation is obtained by directly irradiating the CsI clusters in the ICR cell with a tunable EKSPLA NT 342B UV/VIS OPO. A wavelength range of 225 to 350 nm is covered, where dissociation is found from 225 up to 260 - 290 nm (depending on the cluster size).
The partial photodissociation cross section for every fragment is calculated and furthermore a comparison with the photodissociation cross section of Cs2I+ with a theoretically calculated spectrum is done.
Gas phase studies have provided significant contributions to the understanding of activated CO$_\text{2}$. The metastable CO$_\text{2}^{\bullet-}$ is stabilized by a solvation shell and CO$_\text{2}^{\bullet-}$(H$_\text{2}$O)$_\text{n}$ can be studied readily by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. An EKSPLA NT277 optical parametric oscillator system is coupled into the reaction cell, covering the 2235-4000 cm$^\text{-1}$ region at 1000 Hz pulse repetition rate. CO$_\text{2}^{\bullet-}$(H$_\text{2}$O)$_\text{n}$ (n ≈ 43) is studied via IR photodissociation spectroscopy. The products of the reaction between CO$_\text{2}^{\bullet-}$(H$_\text{2}$O)$_\text{n}$ and small organic molecules are investigated. This provides information about the formation of covalent bonds and thermochemical data via nanocalorimetry.
As sodium chloride is the main component of marine aerosols, the present study shows experimental investigations with theoretical support on the photodissociation cross section of sodium chloride clusters doped with glyoxylate ([Na$_n$Cl$_{n-2}$(C$_2$HO$_3$)]$^+$, n = 5-11). It was found that that the glyoxylate can be photolyzed into HCO and a carbon dioxide radical anion, which is known to be metastable in the gas phase. The salt environment, however, stabilizes the radical anion. Importantly, this fragmentation happens not only in the deeper UV, but also in the wavelength range from 300-400 nm, which is relevant for tropospheric chemical reactions.
Hydrated singly charged metal ions doped with carbon dioxide, $M(CO_2)(H_2O)_n~^+$ $(M=Co,~Mg;~n<50)$ in the gas phase are valuable model systems for the electrochemical activation of $CO_2$. These systems are studied by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry combined with laser spectroscopy. Since mass spectrometry does not yield direct structural information, the presence of an interacting $CO_2$ molecule was tested via the exchange against $O_2$. Reaction rate constants $k_{abs}$ and thermochemical information are extracted from the data in a nanocalorimetric analysis, where average cluster sizes and integrated intensities of reactants and products are modelled with differential equations. Furthermore, absorption spectra are measured with the combination of tuneable OPO laser systems.
Ethyl tert-butyl ether (ETBE) is an upcoming groundwater pollutant in Europe whose environmental fate has been less investigated, thus far. In the present study, we investigated the in situ biodegradation of ETBE in a fuel-contaminated aquifer using compound-specific stable isotope analysis (CSIA), and in situ microcosms in combination with total lipid fatty acid (TLFA)-stable isotope probing (SIP).
Along with the evolution of the laser technologies, the idea to develop a new type of lightning protection based on lasers has emerged in recent years. The goal of the European funded LLR project is to investigate and develop a lightning protection based on the use of upward lightning discharges initiated through a high repetition rate multi terawatt laser. The feasibility of the novel technique is based on recent research providing new insights into the mechanism responsible for the guiding of electrical discharges by laser filaments, on cutting-edge high power laser technology and on the availability of the Säntis lightning measurement station in Switzerland.
The treatment of radiative heat transfer in arc simulation is difficult due to the large temperature inhomogeneity. Line-by-line integration of the radiative transfer equation is prohibitive due to the large computational effort needed. Therefore, the spectrum (e.g. $10^6$ wavelengths) has to be reduced to a suitable number of bands (order 10). As the temperature variation is large, scaling assumptions used in standard methods from combustion may not be valid.
For arcs in Argon, we discuss possible approaches for an automatic generation of bands using clustering algorithms from machine learning. The number of bands for an accurate description of heat transfer is verified for a typical arc profile. Different algorithms and their performance are compared.
The scrape-off layer (SOL) sets the boundary conditions of a tokamak, determining the plasma confinement, the heat exhaust, the impurity levels, and controlling the fuelling of the device. Therefore, a first principles understanding of the physical mechanisms governing SOL turbulence is crucial on the way towards fusion energy. We describe SOL simulations carried out by using GBS, a three-dimensional numerical code that solves the drift-reduced Braginskii equations for the two-fluid model of the plasma and consistently includes neutrals dynamics as well. In this work, results from GBS simulations are used to understand the tokamak fuelling.
The non-adiabatic response of passing electrons near low order Mode Rational Surfaces (MRSs) lead to fine radial structures on ion-scale microinstabilities. It has been shown that these structures persist in the non-linear turbulent regime and lead to the corrugation of density, temperature and zonal flow profiles. This effect significantly affects the turbulent fluxes of heat and particles as shown using local and global gyrokinetic simulations [Dominski, Phys. Plasmas 24, 022308 (2017)]. We have pursued this study by addressing how turbulent transport is affected by the density of low order MRSs, which is varied by considering either different values of magnetic shear or of the minimum toroidal mode number.
The Poster Session is held on Wed and Thu. All posters are to be presented on both days. However, due to technical reasons, the contributions are only listed in the timetable of Wed.
We show that a refractive index varying continuously in space, e.g. due to optical excitation, may not be approximated by a rectangular function as it is common usage in the evaluation of pump-probe spectroscopy. For the example of a terahertz probe wave, we demonstrate the importance of the excitation depth and that approximative solutions may lead to an erroneous data interpretation.
In this work we designed and built an integrated waveguide three-path interferometer for measuring so-called higher-order interferences. These hypothetical higher-order interference do not occur in ordinary quantum mechanics or classical electrodynamics and thus the experiment tests the foundations of physics. Mechanical shutters could switch the interferometer arms on and off individually. Our main goal was to avoid cross-talk between the shutter state in a path and the transmissivity or phase in any other path. Using a laser source we were able to measure higher-order interference to an upper bound of $\kappa = 5(6) \cdot 10^{-4}$, normalized to the two-path interference.
We are setting up an experiment which combines cavity-assisted measurements with a tunable Fermi gas of $^6$Li to study the transport properties of mesoscopic devices.
We will take advantage of a high-finesse cavity to implement a non-destructive measurements procedure to monitor in real time the dynamics of the system and to increase the sensitivity by reducing the preparation noise.
In my poster, I will give a detailed description of the current status of the experimental setup and I will discuss the preliminary test that have been performed on a cavity prototype.
An ion held in a radiofrequency trap interacting with an ultracold buffer gas enables studying two- and many-body physics in a regime of intermediate interaction strengths, including collisions and chemical reactions at very low energy. During elastic ion-atom collisions energy is transferred between the thermal motion of the ion and the RF field, leading to multiplicative fluctuations of the ion’s energy and a power-law tail in the energy distribution. We present an analytical model of this process derived through the formalism of superstatistics and compare the predicted power-law exponent to the results of numerical simulations, confirming the ability to fine-tune the energy distribution of the ion by altering experimental parameters.
The formation of positive and negative ions within doped clusters via electron ionization and electron attachment, respectively, opens a door to insights into cluster characteristics. For example, in case of electron attachment the stabilisation of the dopant anions by the cluster environment may occur. Furthermore, the understanding of the electron attachment process itself can be extended to the low temperature range. Here, a study of neon clusters doped with CO2 is presented and compared to earlier results for pure CO2 cluster beams and helium droplets doped with CO2. All data was collected by means of mass spectrometry
Several experiments at CERN aim at testing the CPT-theorem and weak equivalence principle using antimatter, among them the AEgIS experiment. Here, antihydrogen - produced via resonant charge exchange - will be used for precision measurements where the achievable sensitivity is determined by the temperature of the antiprotons.
We are investigating laser-cooling of anionic molecules to sympathetically cool antiprotons. A test setup to produce cold C2- molecules is currently being commissioned. This will be presented together with theoretical studies on the feasibility of several laser-cooling schemes.
The unprecedented laser-cooling of anions would also enable sympathetic cooling of any other negatively charged species, opening new opportunities in a variety of research areas.
The Poster Session is held on Wed and Thu. All posters are to be presented on both days. However, due to technical reasons, the contributions are only listed in the timetable of Wed.
In femtosecond optical transfection and nanosurgery, cell survival critically depends on phototoxicity. We demonstrated on fixed cells that the use of femtosecond third order phase pulses (Airy pulses) could modulate the photon-interaction in cells leading to a better membrane poration efficiency energy per pulse than bandwith limited femtosecond pulses.
We also discuss results from a live cell experiment. We set up a protocol where we investigate cell viability as a function of pulse spectral phase. Hence, we present an ad hoc protocol based on the use of three fluorophores to assess cells viability at different time points after poration.
The Thin-TOF PET (TT-PET) project aims at the construction of a positron emission tomographer based on silicon sensors with very high time resolution. Using TCAD simulation, a monolithic silicon pixel sensor aimed at 30 ps time resolution was designed and the properties of several test chips were measured. The sensor characteristics and the first comparison of the lab measurements with the simulations will be presented.
Optical biosensors based on photonic crystal surface waves offer a possibility to study binding interactions with living cells, overcoming a problem of a low penetration depth into the cells. Moreover, simultaneous excitation of s- and p-polarized surface waves is realized here, allowing for unambiguous separation of surface and volume contributions to the signal. In this work, we developed functionalization to attach bacteria and performed real-time experiments on antibody binding. Binding of monoclonal antibodies against lipopolysaccharides was analyzed by a nonlinear regression, resulting in the dissociation constant KD = 6.2+-3.4 nM. To our knowledge, this is the first demonstration of antibody binding kinetics to living bacteria by a label-free optical biosensor.
In a cyclotron-based proton therapy facility, the energy selection is performed by means of a degrader. The interaction of the proton beam
with the degrader creates low energy tails that alter the beam quality. The analysis of the degraded energy spectra is hence important,
not only to better understand the performance of an existing facility such as PROSCAN at the Paul Scherrer Institut (PSI), but also to support
the development of new facilities. An accurate analysis of the energy spectrum from the PSI degrader has been performed with Monte Carlo and particle tracking codes and used to support the design of the a superconducting gantry.
The goal of the SAFIR project is to build a pre-clinical PET insert for an existing 7T MRI scanner, with a high temporal resolution of better than 5s per image.
The SAFIR PET insert was modeled by means of the Monte-Carlo tool Gate, and for a simplified mouse model different time dependent tracer activities were simulated. After coincidence sorting, the images were analytically reconstructed with the STIR library and further analysed with PMOD, to obtain time activity curves per region.
This allows comparing the recovered activity curve to the simulation input activity function to assess scanner performance in dynamic acquisitions.
Polydisperse suspensions of pNIPAM microgel particles show a unique, spontaneous particle deswelling behavior. Beyond a critical concentration, the largest and softest microgels deswell and thereby reduce the polydispersity of the suspension. We have recently unraveled the mechanism of this spontaneous deswelling triggered by the percolation of the counterion clouds of the microgel particles, which leads to an increase of free counterions and osmotic pressure outside but not inside the microgel particles. We find particles to deswell when the resulting osmotic pressure difference between the inside and the outside becomes larger than their bulk modulus. We also find this spontaneous particle deswelling to affect the phase behavior of the studied suspensions.
Rotationally tunable diffractive optical elements (DOEs) consist of two stacked
diffractive optical elements which are rotated with respect to each other around their central optical axis. The combined diffractive element acts as a highly efficient diffractive lens, which changes its optical power as a function of the mutual rotation angle. Here we show that the principle can be extended to produce polychromatic tunable lenses, i.e. lenses which have the same optical power, and the same diffraction efficiency within the full tuning range at three or more selectable wavelengths. The basic principle is to use higher order DOEs, which will be polychromatic at harmonics of a fundamental wavelength.
The Poster Session is held on Wed and Thu. All posters are to be presented on both days. However, due to technical reasons, the contributions are only listed in the timetable of Wed.
The accurate modeling of transition-metal compounds (TMC) is essential for their deployment as electrodes of Li-ion batteries.
Allowing to capture the localization of electrons during charge/discharge, Hubbard-augmented DFT functionals (DFT+U) have become the standard choice for the modeling of TMC when computational efficiency is required. This work shows how an extended formulation of DFT+U, including on-site (U) and inter-site (V) interactions, improves the description of the equilibrium structure and the electronic properties of mixed valence cathode materials as Li$_x$MPO$_4$ and Li$_x$CoO$_2$. In particular, the use of computed interaction parameters is shown to be crucial to assess the stability of intermediate compositions and to evaluate the voltage of the battery.
We measured the in-plane optical conductivity spectra between 0.01 and 4eV of (Sr1-xLax)2IrO4.Our data confirm that Sr2IrO4 is a Mott insulator with a gap onset at about 0.1eV.La substitution leads to a rapid collapse of the gap which is completed for x=0.05, and the emergence of a narrow-mode associated to free charge carriers. The intensity of this mode as compared to the nominal carrier doping reveals a very rapid transfer of high energy spectral weight above the gap down to the free-carrier sector. The free-carrier optical conductivity displays “bad” metal-like behavior as a function of temperature and frequency,with indications of a partial gapping of the free-carrier response of about 30meV.
We present an angle resolved photoemission spectroscopy study of the overdoped cuprate superconductor $La_{2-x}Sr_xCuO_4$. Using the symmetry properties of the photoemission matrix element effect, we present on this poster the orbital character of the band structure. With the obtained information, consequences for superconductivity and pseudogap physics is discussed.
High temperature superconductivity, colossal magneto-resistance and many other intriguing phenomena in correlated electron physics arise in doped Mott insulators. Here, we present the first angle-resolved photoemission (ARPES) study of electron-doped Ca$_{2}$RuO$_{4}$. The undoped parent compound of our study has been investigated intensely as a model system of a multi-band Mott transition. Our ARPES data reveal a coherent Fermi surface at doping levels as low as 0.11. In contrast to cuprates or iridates, the emergent metallic state is characterized by heavy quasiparticle bands devoid of a pseudogap. These results show that key-properties of doped cuprates and iridates, such as the momentum dependent pseudogap are not universal features of doped Mott insulators.
In the past years, magnetism-driven ferroelectricity has been reported in a number of frustrated magnets with spiral magnetic orders. Such materials are of high current interest due to their potential for spintronics and low-power magnetoelectric devices. However, their low magnetic order temperatures (typically <100K) restrict their fields of application.
In this talk I will show that chemical disorder is a powerful tool that can be used to stabilize magnetic spiral phases at higher temperatures. As example of this novel mechanism I will present our recent investigations on YBaCuFeO5, where a controlled manipulation of the Cu/Fe chemical disorder was successfully used to increase the spiral order temperature from 154 to 310K.
It is becoming clear that strong electron interactions with other electrons and with the magnetic excitations unify all iron-based materials, and probably, all unconventional superconductors in general. I will review the electronic self energy, determined from the angle-resolved photoemission spectroscopy (ARPES) for the 11, 111, 122, and 1111 families, and will compare it to the situation in the compounds of other transition metals. I will show how the spectral features at the energy scale of the whole $3d$ band match with the results of calculations for correlated systems and how the low-energy features correspond to the peculiarities found in the spin-fluctuation spectrum measured in neutron scattering.
The strength of the electron-phonon coupling in the superconducting mechanism of n-doped STO is still under debate. Interestingly, it has been proven that SrTiO$_3$ becomes ferroelectric at low temperature when $^{16}$O atoms are substituted by their isotope $^{16}$O. Using DC resistivity and AC susceptibly measurements we have determined the effect of $^{18}$O/$^{16}$O isotope substitution on T$_c$ and H$_c$. We observed a factor 1.5 increase of T$_c$ and H$_{c2}$ at any doping levels. This isotope effect is opposite to BCS theory, but anticipated by models of polaronic band narrowing, as well as proximity to a ferroelectric quantum critical point.
Making connections between various domains of modern physic is an exciting opportunity. The spontaneous symmetry breaking of the crystal structure of hexagonal manganite creates an almost perfect Mexican hat potential. We have performed polarization resolved Raman spectroscopy of ErMn$O_3$ and two types of InMn$O_3$. In ErMn$O_3$, the phonons that have a substantial overlap with the Higgs amplitude mode show an unusually strong red softening on warming. In contrast the frequencies of the corresponding modes in InMnO$_3$ are largely temperature-independent. These results are consistent both qualitatively and quantitatively with our combined Landau and ab initio model describing the coupling between the Higgs and the Goldstone-like mode in the hexagonal manganites.
We report a comprehensive investigation of the structural, electric transport, magnetic, and thermodynamic properties of Na2.7Ru4O9 and NaRu2O4 single crystals. The compounds are structurally different; Na2.7Ru4O9 crystalize in monoclinic (C 2/m) structure while NaRu2O4 crystalize in orthorhombic (P 21/ma) structure. We observed a first-order phase transition in the electrical resistivity at Tc = 365K and Tc = 530 K for Na2.7Ru4O9 and NaRu2O4, respectively. Resistivity is influenced by electron–phonon scattering and additionally inter-band electron scattering and the evidence for metal-like electronic contribution in heat capacity was also observed. The electronic contribution to the specific heat (gamma) for Na2.7Ru4O9 and NaRu2O4 was determined to be 26.91 and 3.93 mJ/mol K2, respectively.
The Poster Session is held on Wed and Thu. All posters are to be presented on both days. However, due to technical reasons, the contributions are only listed in the timetable of Wed.
A new and promising technique to study the dynamics on an atomic scale in hard condensed matter uses high flux coherent X-ray radiation. The technique is called Atomic scale X-Ray Photon Correlation Spectroscopy (aXPCS). Since new X-Ray sources have become more powerful in recent years the question of influence of X-rays on materials is becoming more important. Here the effect of the beam on many different materials is presented. By comparison between the different species first conclusions about the effect are drawn. Additionally quantitative and qualitative results on all of the investigated materials are presented in detail.
Two well studied compounds $Sr_{3} Cr_{2} O_{8}$ and $Ba_{3} Cr_{2} O_{8}$ are insulating dimerized antiferromagnets with magnetic ions. These ions are located in hexagonal bilayers with a strong intradimer antiferromagnetic interaction, that leads to a singlet ground state and gapped triplet states We report on the effect on the structural and magnetic properties of the spin-$\frac{1}{2}$-dimer system, $Sr_{3} Cr_{2} O_{8}$, by introducing chemical disorder. Two large single crystals of $Ba_{3-x} Sr_{x} Cr_{2} O_{8}$ were grown. The structural and magnetic properties of these compounds were studied by magnetization, heat-capacity and inelastic neutron scattering measurements. These results show a noticeable change in the magnetic properties by a random substitution effect.
In this work, we present calculation of the Y NMR shielding in
intermetallic compounds. (YM, YMX, YM$_{2}$X, YM$_{2}$X$_{2}$, Y$_{2}$MB$_{6}$ and Y$_{2}$MSi$_{3}$ where M represents various transition metals and X refers to Si, Ge, Sn). The total shift $\sigma$ of this selection varies by about 2500 ppm and correlates very well with the experimentally observed shielding except for YMg and YZn. The diamagnetic contribution $\sigma_{o}$ (chemical shift) is not constant and varies up to 1700ppm. Half of our compounds have a paramagnetic (negative) $\sigma_{c}$ due to reoccupation of the valence Y-5s electrons, while for others the induced Y-4d magnetic moment induces diamagnetic core contributions.
We studied the $T$&doping-dependence of the energy-loss function of bilayer and trilayer Bi-cuprate by ellipsometry to obtain information on the energy stored in the Coulomb interaction between the conduction electrons,on the $T$-dependence thereof,and on the change of Coulomb interaction when Cooper-pairs are formed. As $T$ drops through $T_c$,the loss function's integral $\leq2eV$ displays an abrupt change of $T$-dependence as compared to the normal state. This effect at$\simeq T_c$depends on doping,with a sign-change for weak overdoping. Based on our observations we decide whether or not the Superconducting phase transition is driven by the saving of Coulomb energy for small momentum and discus its implications for the mechanism of high$T_c$superconductivity.
Both matter and language are dynamic systems constantly in motion. Language dynamics can lead to so-called language shift when people give up use of their language for another. We show that it is possible to study language shift on a large scale by using methods from diffusion physics. We present a microscopic model for language diffusion [1] and its application to data on minority languages in Austria and Hungary. Our model allows us not only to identify the driving factors for language shift, but also to follow deviating local processes such as the different dynamics in urban areas.
[1] Prochazka K, Vogl G (2017) PNAS 114(17): 4365–4369
The Brill transition is a phase transition process in polyamides, that has been related with structural changes between the hydrogen bonds of the lateral functional groups (C=O) and (N-H). In this study we show the potential of Raman spectroscopy for exploring this phase transition in polyamide PA66 (nylon 6,6). Raman spectra were collected during a step by step heating and cooling process of the sample from 30°C to 240°C, allowing to grasp signatures of the Brill transition from peak parameters of specific vibrational modes, and to verify the Brill transition temperature as well as the reversibility of this phase transition.
The main goal of the Interreg Italy-Austria ITAT1023 InCIMa project (2017-2019), as cooperation between Elettra Sincrotrone Trieste, University of Salzburg and Salzburg University of Applied Sciences, is the establishment of a cross-border infrastructure for the synthesis and characterization of functional smart materials, through the exploitation of spectroscopic techniques that employ radiation from far infrared to hard X-rays. The cooperation will be realized by the synergic complementation and the improvement of several analytic techniques and synthetic approaches for the optimization at present of two material types: totally natural rigid foams derived from by-products of wood industries, and plasmonic metamaterials to be used in the infrared and ultraviolet spectral range.
Samples of totally natural rigid foams, derived from byproducts of wood industries, have been characterized through the exploitation of state-of-the-art spectroscopic techniques combined with imaging and mapping options employing a wide range of electromagnetic radiation from far infrared to X-rays. The synergistic complementation of several analytic techniques available through the beamlines IUVS (UV-Raman), SISSI (Infrared), and SYRMEP (microtomography) at the Elettra Sincrotrone Trieste, triggered with the help of the CERIC proposal 20167027, will enable to optimize, in future subsequent steps, these materials with potential applications as new materials for green-building technology, as well as possibly for water purification from contaminants of emerging concern.
Detailed characterization by means of confocal Raman microscopy of interfaces present in the raw material formulations of several PLA 3D printing filaments, as well as in 3D shaped bodies, have been performed in order to gain information on polymer/polymer interfaces, these having a decisive influence on the mechanical properties as well as the formability or the homogeneity of the final material. This study has been done within the project Interreg Bayern Austria AB97 TFP-HyMat, having as target the establishment of a cross-border technology and research platform for the production and processing of hybrid materials, using as example biogenic filaments for 3D printing.
The Poster Session is held on Wed and Thu. All posters are to be presented on both days. However, due to technical reasons, the contributions are only listed in the timetable of Wed.
Regular arrays of single atom magnets represent model systems for information storage at the ultimate length scales. Individual rare-earth atoms on decoupling layers have recently received great attention for showing extraordinary magnetic stability; however, they still lack spatial order. Here we report a self-assembled superlattice of individual and noninteracting Dy atoms on graphene grown on Ir(111), with magnetic hysteresis up to 5.6 T and spin lifetime of 1000 seconds at 2.5 K. The observed magnetic stability of Dy atoms is a consequence of the low intrinsic electron and phonon densities of graphene and the six-fold symmetry of the Dy adsorption site [R. Baltic et al., Nano Lett. (2016), DOI: 10.1021/acs.nanolett.6b03543].
Recently it was shown that an end-user 3D printer can be used to print polymer bonded rare-earth magnets with a complex shape. The focus here is to manufacture polymer bonded NdFeB magnets for producing a tailored external field in a specific region outside the magnet. To determine the desired magnetization or shape of the printed magnet we developed an inverse stray field method and a topology optimization algorithm based on finite elements that allows us to deduce the magnetization and the shape of the magnet, respectively. With this simulation framework magnets are designed and printed.
Nanocrystalline Fe3O4 thin films were grown by adopting two different reduction approaches (1) vacuum annealing (2) wet H2 annealing. While vacuum annealed films shows Verwey transition with lower resistivity compared to the bulk Fe3O4, the same are not observed in electric transport properties of wet H2 annealed films. However, this transition was clearly seen in the temperature dependence of magnetizations of both sets of Fe3O4 thin films. This seems to indicate that the both electric transport and magnetization are independent processes; it’s just coincidence to happen at same place of Verwey transition at 120 K. Different electric transport properties in both reductions treated Fe3O4 films will be discussed.
We report the formation and magnetic properties of metallic cobalt-core
and oxide shell structured nanoparticles upon oxidation of Co
nanoparticles with molecular oxygen under ultra-high vacuum conditions.
The presence of a core-shell structure was confirmed with HR-STEM while
x-ray photoemission electron microscopy shows that the core remained
metallic and magnetic at low oxygen dosage, with CoO as the oxide shell.
At higher oxygen dosages CoO and Co3O4 form the oxide shell and the
core loses its magnetic contrast. These results show that the presence of
high magnetic anisotropy in Co nanoparticles does not arise from a surface
anisotropy contribution.
A charge current flowing through a nonmagnetic conductor induces a spin current perpendicular to both the current direction and the spin polarization due to the spin Hall effect (SHE). Due to the nature of the SHE, most spin accumulation detection methods rely on the utilization of adjacent ferromagnets. We report here the first direct measurement of the current-induced interfacial spin accumulation due to the SHE in Pt and W thin films by magneto-optical scanning Kerr microscopy. Our measurements, combined with first principle electronic structure calculations of the SHE and magneto-optic response of Pt and W, yield quantitative estimates of the spin Hall angle and spin diffusion length in nonmagnetic conductors.
Magnonic crystals (MCs) allow for tailoring the dispersion relation of spin waves (SWs) in nanopatterned ferromagnets. Local defects in MCs are expected to add further functionality. We prepared 1D MCs consisting of bistable magnetic stripes separated by sub-100 nm air gaps. By adjusting the magnetic history, we programmed ordered magnetic states with single stripes of opposed magnetization. We studied the influence of these defects on propagating SWs via broadband microwave spectroscopy and phase-resolved focused Brillouin light scattering microscopy. Depending on a bias magnetic field, we observed SW attenuation and phase shift cause by the magnetic defects. We thank for funding by SNSF via grant 163016.
The chiral ferrimagnet Cu2OSeO3 hosts topologically protected spin textures known as magnetic skyrmions. It has been shown to provide novel functionality in microwave technology due to e.g. dichroism. We conducted broadband spin-wave spectroscopy on different single crystals of Cu2OSeO3 with magnetic fields applied in different orientations. In the field-polarized phase at 5K we observe numerous sharp resonances that we attribute to discretized spin waves in the mm-long crystals. Their observation substantiates a very low damping parameter which is key for microwave applications. Support by DFG TRR80, DFG FOR960, ERC Advanced Grant 291079 (TOPFIT) and SNSF Sinergia Network NanoSkyrmionics CRSII5 171003 is acknowledged.
The core-free magnetic configuration of ferromagnetic nanotubes leads to a controllable and fast reversal process and makes them promising candidates for high-density data storage, magnetic sensors, and logic device elements. We explore the magnetic configurations of different individual ferromagnetic nanotubes that we deposited on semiconductor nanowires of GaAs. Nanotubes prepared from permalloy or CeFeB have diameters ranging from 130 to 200 nm and a length in the range of 5 - 20 micrometers. We perform measurements on the magnetoresistance and anomalous Nernst effect. The research is funded by the DFG via GR1640/5-2.
Interconnected nanomagnets periodically arranged in one and two dimensions, called magnonic crystals, have been shown to provide tailored band structures for spin waves. The same has been found for antidot lattices. Aperiodic tilings and so-called artificial quasicrystals are far less explored. We fabricated nanopatternd holes in CoFeB thin films that were arranged in a Penrose tiling. Using broadband spin wave spectroscopy, we studied the absorption of microwaves and the propagation of spin waves. We observed characteristic sets of resonances in both the absorption and transmission experiments. We interpret the results in terms of dispersive eigenmodes of the quasicrystalline nanohole lattices. This work was supported by SNF via grant number 163016.
Magnonic crystals are a novel type of artificial crystals formed by the periodic arrangement of magnetic nanostructures and magnetic skyrmions [1] are topologically stable spin textures, generally stabilized by Dzyaloshinskii-Moriya interactions [2]. Key challenges regarding the skyrmion lattice are to stabilize and confine them. The aim of the present work is to stabilize and confine the magnetic skyrmions by patterning a nanometer size antidot lattice in high perpendicular magnetic anisotropy films. The observations are very important for future magnon spintronic devices based on skyrmion lattices.
References:
[1] D. A. Gilbert et. al., Nat. Commun. 6, 8462 (2015).
[2] O. Boulle et. al., Nat. Nanotech. 11, 449 (2016)
One of our primary areas of research is artificial spin ice, which consists of specific arrangements of nanomagnets that display analogous behavior to their real crystal counterparts such as the rare-earth Pyrochlore compounds. We have earlier investigated static/quasi-static responses of well-known structures, such as artificial square and kagome spin ices, and our current efforts are on probing for magnetization dynamics. Frustration, when combined with topological defects, leads to dynamics that are geometry specific. We investigate the temperature dependent response of the nanomagnet arrays using Photoemission Electron Microscopy.
The control over the aggregation of magnetic ions in a non-magnetic semiconductor matrix constitutes a new way to realize semiconductor/ferromagnetic nanocomposites with yet unexplored but striking functionalities. In this work we show that it is possible to obtain a controlled and well-defined arrangement of single-phase magnetic Fe-rich nanocrystals embedded in a GaN matrix [1]. We observe a phase-separation occurring already above 0.4% of iron ions, leading to the formation of Fe-rich nanocrystals with particular stoichiometry and magnetic properties. The significance of these results is discussed in view of prospects for spintronic devices.
[1] A. Navarro-Quezada et al. Appl. Phys. Lett. 101, 081912 (2012)
Artificially designed arrays of nanostructures with a microstructure at sub-micrometer length scales can exhibit unique functionality, especially when built from a combination of different classes of materials. We present an overview of a novel magneto-mechanical metamaterial, where the coupling between nanoscale magnets embedded in a soft polymer matrix is exploited to control its mechanical properties. In addition, we elaborate on the possible applications unlocked by this new system. Different approaches to the realization of such a material using lithography, 3D laser lithography and nanoparticle dispersions are expanded upon. Finally, we present the most recent results involving fabrication and characterization of magneto-mechanical properties of our proposed metamaterial.
In contrast to well-known models such as the Heisenberg model, which just incorporate the notion of the nearest neighbour, the anisotropic dipolar interaction directly depends on the geometry of the lattice and therefore its symmetries. These symmetries should be reflected by the properties of a possible phase transition in that system. To study these effects we employ the Monte Carlo Renormalization Group technique since this method can provide precise estimates of the critical exponents. We will show our latest results for the 2D XY dipolar interacting square lattice and other related systems.
Correlations in low-dimensional magnetic systems result in interesting properties, especially if continuous spin degrees of freedom are involved. Here we observe the magnetic correlations of dipolar-coupled artificial XY moments (circular nanomagnets) on a square lattice as a function of temperature using low-energy muon-spin relaxation. For strong interactions between the nanomagnets, we observe the onset of slow collective dynamics below a tunable critical temperature. In contrast, the dynamics in weakly-interacting systems is described by the blocking of individual nanomagnets which happens at considerably lower temperatures.
The Poster Session is held on Wed and Thu. All posters are to be presented on both days. However, due to technical reasons, the contributions are only listed in the timetable of Wed.
Surface-enhanced Raman spectroscopy (SERS) is a promising characterization technique for biomedical diagnostics usable for quick identification of cells, tissue and bacteria. The aim of our study is to analyze the SERS performance of new, promising SERS substrates and to compare their performance with commercial ones.
Large area prototypes of homogenous SERS substrates were created from microstructured polymer slide and coated with Ag via a PVD process. A chemical post-treatment then produced Ag nanoparticles at the substrate surface. In order to check the enhancement factor, 532 and 780 nm laser excitation wavelengths were used to collect Raman spectra from 1,4-benzenedithiol deposited on our own substrates and on commercial reference substrates.
Crystalline films of small semiconducting organic molecules on two-dimensional materials like graphene or ultrathin hexagonal boron nitride (hBN) offer attractive potential for fabricating organic solar cells, organic light emitting diodes, and organic field effect transistors on flexible substrates. Here, we report on the growth of the polar, acene-like molecule dihydrotetraazaheptacene (DHTA7) on hBN. µm-long crystalline needles are observed which are oriented close to armchair directions of the substrates with a 9° deviation which originates from the dipolar interaction of the molecules as demonstrated by DFT calculations. Results are compared to needle growth of the nonpolar parahexaphenyl molecule 6P on hBN [1].
[1] Matković, et al., Sci. Rep. 6, 38519 (2016).
Combined hydration/dehydration processes of oxide/hydroxide systems - e.g. CaO/Ca(OH)2 - can be used for storage of industrial excess heat. Exothermal hydration of CaO is fast and complete at ambient temperature; however, dehydration requires high temperatures. A system operable at lower temperatures would be desirable.
A candidate is the system MgO/Mg(OH)2. However, hydration of the oxide is incomplete at room temperature. Studies of the adsorption behaviour of water on MgO-surfaces suggest kinetic reasons. A previous DFT study found that water does not dissociate at MgO-surfaces, whereas on CaO-surfaces hydroxyls are formed.
In the present work we investigate the effects of Ca-doping of the (001)-MgO-surface on the formation and stability of hydroxyls.
An amorphous ultra thin W foil with a thickness of 2 nm was deposited on an amorphous 3 nm carbon foil by electron beam- physical vapor deposition. The specimen was analyzed in an aberration corrected scanning transmission electron microscope (STEM) under ultra high vacuum condition. During the observation the amorphous structure of W converts to a partially nanocrystalline structure. The crystal phase structures are analyzed by Fast Fourier Transformation calculated from high angle annular dark field (HAADF) images. In addition, the surface diffusion of W atoms could be observed and measured in continuously acquired HAADF images.
Compared to bulk systems, in the two-dimensional realization of electron liquids, correlation effects are much more pronounced, key examples being the collective modes such as plasmons and magnons. Taking care of these effects leads to substanially lower excitation energies. For highly dilute semiconductor quantum wells it is mandatory to account for dynamic multi-particle fluctuations, which substantially decrease the collective mode even further and introduce finite lifetime to the mode. A spin sensitive study of the electron system promises new insights via the longitudinal spin plasmon and a highly interesting 'magnetic antiresonance', where both (spin-spin response and spin-density response) vanish.
The Poster Session is held on Wed and Thu. All posters are to be presented on both days. However, due to technical reasons, the contributions are only listed in the timetable of Wed.
The ATLAS experiment is planning a major upgrade of its tracking detectors during the Phase-II LHC shutdown, to better take advantage of the increased luminosity of the HL-LHC. To this end, new CMOS sensors are being developed. The Edge-Tracient Current Technique (eTCT) measurement method and its latest subsequent preliminary results on the TowerJazz 180nm CMOS technology sensor are presented. New mechanical supports (or staves) are also being prototyped, the thermal characterisations methods and readout system for which are also discussed.
The prospects of an implementation of Lloyd's Mirror with very-cold neutrons at the Institut Laue-Langevin are investigated. Lloyd’s Mirror is a free-space interferometer similar to the double-slit experiment, but with a vertical mirror on the beam axis.
This interferometer was suggested to probe physics beyond the standard model of particle physics i.e. dark matter and dark energy models. Here concrete measurement scenarios and the achievable sensitivity is presented. The estimation of the expected sensitivity is based on previously measured beam characteristics of the shaping section at the very-cold neutron beam at the PF2 at the Institut Laue-Langevin.
One class of gravity experiments within the qBounce project focuses on the realization of a Quantum Bouncing Ball, in particular a measurement of the time evolution of a neutron bouncing above a horizontal plane.
We measured the spatial probability distribution of this Schrödinger wave packet for different observation times with a spatial resolution of about 1.8μm.
We illustrate the role of interference weaving the quantum carpet of several quantum states. After a first quantum reflection, several snapshots show the fall of the wave packet.
Physics beyond the Standard Model (SM) is required to understand many unexplained features, both of particle physics and of cosmology. Precision measurements in neutron beta decay allow searching for physics beyond the SM.
The PERKEO III collaboration performed a measurement of the proton asymmetry C, which describes the angular correlation between the momentum of the decay proton and the spin of the neutron. In the SM, neutron decay is covered within the framework of V-A theory. All asymmetry parameters depend only on the ratio of axial-vector coupling constant (gA) over vector coupling constant (gV).
We will present preliminary results of the last measurement period.
Proton-proton collisions at LHC can be used to study Central Exclusive diffractive Production (CEP). In CEP the scattering protons remain intact, but exchange sufficient energy to create a new particle X at central rapidity. Experimentally these events are identified by their rapidity-gap topology, with particle production at small rapidities and particle voids at larger rapidities. The centrally produced X is studied by its decay into pairs of pions and kaons.
In this poster we present a CEP study carried out with the ALICE detector. Special emphasis is put on the X-mass region below 2.5 GeV/c2 which hosts a number of known scalar mesons and presumably also the lightest glueball.
The AEgIS Collaboration at CERN will perform the world’s first direct measurement of the Earth´s gravitational acceleration on antimatter, by sending an antihydrogen beam through a classical deflectometer.
I will present a detector for a first measurement of the gravitational effects on an antimatter system. The detector consists of pure Caesium Iodide crystals and commercially available Silicon Photomultipliers to measure the light produced in the corresponding annihilation processes. The CsI crystals decay times and spectra were characterized using a Na²² source at room and at low temperatures. Furthermore, the behaviour of the SiPMs at low temperatures was examined. A measurement at the GRACE line using antiprotons is planned for June.
The Future Circular Collider (FCC) design study plans a high-energy frontier particle accelerator of 100 km circumference to succeed the Large Hadron Collider. Ongoing work on hadronic and leptonic options for the beams of the accelerator are supported by a common software framework (FCCSW) developed at CERN. Great emphasis is put on collaboration and synergies, as for example with the adoption of the A Common Tracking Software (ACTS) project that aims to extract and package the tracking code of the ATLAS experiment. An overview of the hadron-hadron tracking detector design, first results based on parametric, fast and full simulation and their implications for offline computing will be presented.
Although radioactivity is generally assumed to be explained by a Poisson process, with no dependence on atmospheric or cosmological conditions, there have been some indications of time-dependent decay rates and theories including neutrino-induced rate variations. We have developed an experiment dedicated to the long-term measurement of beta decays using NaI(Tl) detectors. Two detectors for each of four sources at four different locations covering both hemispheres as well as continuous monitoring of environmental conditions will allow us to identify and correct for systematic influences. This will give a precise measurement of the sources’ half-lives and put strong constraints on the size of annual modulations.
DAMPE is a satellite-borne experiment in operations since December 2015, capable of detecting high energy cosmic rays and gamma rays. Its calorimeter, corresponding to about 31 radiation lengths allows to study electrons up to 10 TeV, making it the deepest calorimeter in space to date. A major complication at these energies is the discrimination between protons and electrons, as both particles leave similar detector signatures. We propose solving this problem using deep neural networks (DNNs), a fast emerging machine learning technique. DNNs can accurately discriminate between event classes using only basic detector variables, albeit at the cost of computation time. We present the technique and evaluate its performances using simulations.
The LHCb detector will be upgraded during the second long shutdown of the LHC. The current tracking sub-systems will be replaced by the Upstream and the Scintillating Fibre (SciFi) trackers, composed of high-granularity silicon micro-strip planes and scintillating fibres read out by silicon photomultipliers, respectively.
The SciFi tracker consists of three stations each composed of four detection layers. Each detection layer is composed of 12 modules which are themselves composed of 8 fibre mattresses (mats).
This contribution presents a description of the techniques developed to produce 2.5 m-long mats consisting of 6 layers of 250 μm diameter fibres and the associated quality assurance tests.
Muonium, which is the bound state of an antimuon and an electron (mu+e-), is an ideal system to perform fascinating measurements, e.g. fundamental constants, bound-state QED, and the gravitational interaction of antimatter. This poster presents an efficient approach to form muonium using superfluid helium proposed at the Paul Scherrer Institut. This is the first step towards a high-brightness muonium beam. This poster describes the physical processes and the experimental method to measure muonium formation. To this end a cryogenic target is designed with electrodes to test the electric field and temperature dependence of the muonium formation rate.
The Paul Scherrer Institute Neutron Electric Dipole Moment (PSI nEDM) experiment is a room temperature experiment using the Ramsey technique of separated oscillating fields. The PSI nEDM experiment aims to achieve a sensitivity of $d_n\sim<1\times10^{-26}$e$\cdot$cm. Since the main magnetic and electric fields applied to the stored neutrons are flipped regularly, constant residual fields are canceled out. Leakage currents, arising from high voltage system, which are correlated with the electric field may induce a false measurable EDM. A study of the possible pathways taken by the leakage currents will be discussed. Furthermore, we will also present a study which constrains the false EDMs arising from such leakage currents to under $9.62(1)\times10^{-28}$e$\cdot$cm.
Relativistic heavy-ion collisions produce hot and dense strongly interacting matter. Dielectrons (e$^{+}$e$^{-}$) offer a way to investigate, e.g. the temperature of this medium and signatures of chiral-symmetry restoration.
The dominant background in the analysis of dielectrons originates from tracks produced via photon conversions in the detector material. Numerous observables allow for discrimination of this background which motivates a multivariate approach in the classification of dielectrons. Machine learning algorithms were evaluated positively for this purpose. In addition, we present novel methods to reduce the systematic uncertainty inherent to supervised learning on MC simulations, and a status update on the analysis of latest LHC Pb-Pb data.
ALICE, the dedicated heavy-ion experiment at CERN—LHC, will undergo a major upgrade in 2019/20. In this work, we analyze low-mass dielectrons in Pb—Pb collisions after this upgrade. These $e^+e^-$ pairs are, for example, sensitive to the temperature of the collision system. Due to their small signal-to-background ratio, high-purity dielectron samples are required, which can be provided by traditional, cut-based analyses, however at the price of low signal efficiency. We aim to improve on existing methods by employing a multivariate approach to reject combinatorial background, conversion pairs and heavy-flavor contributions to the dielectron spectrum in a scenario involving the planned upgrade of the ALICE Inner Tracking System.
Mu3e is a dedicated experiment for the rare lepton flavour violating decay $\mu^{+} \rightarrow e^{+}e^{-}e^{+}$. Its ultimate goal is to find or exclude this process if it occurs more than once in $10^{16}$ muon decays, a four orders of magnitude improvement.
A thin multi-layer scintillating fibre detector read out on both sides with silicon photomultiplier arrays provides a sub nanosecond time measurement in order to reject combinatorial background at a muon stopping rate ~$10^8$ muon/s, concurrently minimizing the material budget to $X/X_{0}<$~ 0.3%.
The requirements and design of its trigger-less high rate readout chain, including the dedicated readout chip MuTRiG, are presented. It complements the talk “The Mu3e Fiber Detector”.
Understanding the precise rigidity dependence of the carbon flux sheds light on the origin, acceleration and propagation of cosmic rays. The Alpha Magnetic Spectrometer (AMS-02) provides measurements of cosmic rays with high accuracy. Data analysis procedures, focusing on charge selection and efficiency calculations, together with the measurement of the carbon flux based on data collected by AMS in the first 5 years of operation, will be presented.
The LHC operation relies on a good knowledge of the optics, usually corrected in absence of beam-beam interactions. In a near future, both the LHC and the HL-LHC will need to cope with large head-on beam-beam parameters, the impact on the optics needs to be understood and, if necessary, corrected.
The T2K experiment is a long-baseline accelerator neutrino experiment using a near detector complex ND280 and a far detector Super-Kamiokande.
This contribution presents the results obtained with the simultaneous fit of muon neutrino disappearance and electron neutrino appearance, in neutrino and antineutrino mode.
A Markov Chain Monte Carlo method is used to obtain the posterior probability on δCP, sin^2 θ13, sin^2 θ23 and Δm23 from the data of both ND280 and Super-Kamiokande.
The analysis report the best current constraint on the CP violating phase, excluding the CP conserving values at 1σ.
Observations at cosmological and astronomical scales indicate that the majority of matter in our Universe is in the form of non-relativistic and long-lived dark matter. Dual-phase xenon Time Projection Chambers (TPCs) are successfully operated in direct dark matter detection experiments. Silicon Photomultipliers (SiPM) are a favored candidate to detect the scintillation light in the next generation TPCs. Commercially available SiPMs do not fulfill all the requirements imposed by a dark matter detector, hence a dedicated development with the manufacturer is necessary. We present our dedicated low-temperature test facility, together with latest results on the temperature-dependent characterisation of SiPM arrays and optical photon simulations for a future SiPM-based TPC.
The Cherenkov telescope array (CTA) is the next generation of ground-based gamma-ray astronomy and will provide a deep insight into the non-thermal high-energy universe. CTA array will be composed of an array of up to 100 small sized telescopes in the Southern emisphere.
The SST-1M is one of the proposed prototypes for the sub-array.The SST-1M camera is under commissioning at the University of Geneva. The photo-detection plane is composed of SiPM sensors connected to light concentrators.
The SST-1M project will be presented with an emphasis on the latest performance validation tests such as charge resolution, trigger efficiency together with Monte-Carlo comparaison. The shutter test results will be presented as well.
Silicon detectors built in high-voltage and high-resistivity CMOS technology are an interesting options for the pixel tracker needed for the ATLAS experiment upgrade for the high luminosity LHC program. They are less expensive and easier to produce with respect to standard hybrid silicon pixel detectors. This technology must be carefully tested and characterized. One of the techniques used for this purpose is the Transient Current Technique: electron-holes pairs are produced in a precise position of the detector using a IR laser beam, allowing to probe parameters like the depletion depth of the sensor.
TCT measurements have been performed on a demonstrator chip, produced by AMS, before and after proton irradiation.
The Landau damping suppresses the development of coherent particle motion preventing instabilities. In particle accelerators the coupled motion of the circulating particles with the induced wake fields in the accelerator environment is Landau damped by a diversification of particle oscillation frequencies (tune spread). In colliders the tune spread can be generated by non-linear forces such as the beam-beam interactions. At the Large Hadron Collider (LHC) the instability thresholds are evaluated computing the dispersion integral in the limit of excited resonances and diffusive mechanisms that may modify the particle distribution in the beams. Stability studies for different sources of tune spread are presented and compared to experimental observations at the LHC.
The ASACUSA collaboration at CERNs Antiproton Decelerator aims to measure the ground-state hyperfine splitting of antihydrogen to test CPT symmetry. The Rabi-type setup consists of an antihydrogen source and a spectroscopy apparatus made out of a microwave cavity and a sextupole magnet, terminating in a detector.
Previously, this detector consisted of a BGO crystal and two layers of scintillating bars. For 2017s beamtime the detector was modified by incorporating two layers of scintillating fibers. These provide a spatial resolution in the order of millimeter which allows for efficient discrimination of cosmic background and advanced tracking. This contribution covers design and construction as well as results of preliminary performance studies.
The SHiP experiment is a new general purpose fixed target experiment proposed at the CERN SPS accelerator. The experiment will comprise a compact tau neutrino detector and a detector to search for hidden particles. Background rejection is ensured by use of background taggers and a dedicated timing detector. The timing detector will reduce combinatorial di-muon background by requiring incoming particles to be coincident in time within 100 ps. One option for the timing detector consists of columns of horizontal scintillating bars read-out on each end by Silicon Photomultiplier arrays. This study focus on the time resolution of such plastic scintillating bars as would be relevant to the SHiP experiment.
The IceCube detector has observed the first clear detection of a diffuse astrophysical high energy neutrino flux, however, the sources for these neutrinos have yet to be found. IceCube neutrino source searches involve looking for clustering of neutrinos or a strong correlation with known sources observed by other messengers also expected to emit a neutrino flux. The most recent updates will be presented in the search for sources of extraterrestrial neutrinos using an optimized data set of tracks with the addition of 2 more years of data. Results on a possible correlation between ultra-high energy cosmic rays and high energy neutrinos will also be shown.
In order to preserve the structure, and thus the function, of proteins and protein complexes, evolution must mutate amino-acids carefully, trying to introduce concerted changes (e.g. positive/negative charge contact turns into negative/positive charge contact). The simultaneous analysis of the sequences of the same protein from a multitude of organisms highlights where these correlated mutations (co-evolution) has taken place, and this information can be used, in principle, to discover which contacts are important and to consequently predict the structure of as protein and of protein complexes.
Remarkably, this intuitive goal has been hampered for a long time by the inability of algorithms to disentangle between direct and indirect correlations. In 2009 a new algorithm, based on the mapping of the space of sequences on the configurations of magnetic systems, has resolved the problem, and has ushered a new era, where sequence analysis can complement both experimental techniques and other computational approaches.
In this presentation, I will present the state of the art and some applications that have allowed us to propose new protein complexes and the structure of some complexes whose structure has not yet been determined experimentally.
We introduce a numerical scheme to evolve functional elastic materials that can accomplish a specified mechanical task. In this scheme, the number of solutions, their spatial architectures and the correlations among them can be computed. As an example, we consider an "allosteric" task, which requires the material to respond specifically to a stimulus at a distant active site. We find that functioning materials evolve a less-constrained trumpet-shaped region connecting the stimulus and active sites, and that the amplitude of the elastic response varies non-monotonically along the trumpet.
Finally, we show that the success of this architecture stems from the emergence of soft edge modes recently found to appear near the surface of marginally connected materials. Overall, our in silico evolution experiment offers a new window to study the relationship between structure, function and correlations emerging during evolution.
Bacteria and mitochondria share a common ancient evolutionary history, and their division processes involve a similar sequence of shape changes, before they pass through a singular point on their way to becoming two. Nonetheless, as bacteria and mitochondria divide, their composite envelopes are shaped by dramatically different constraints and forces. Bacteria control and maintain their size from generation to generation, using a mechanism of constant elongation per cell cycle. Mitochondria dynamically become fragmented or form fused networks, depending on their metabolic state and that of the cell. However, fundamental questions remain as to how the rates and timing of these processes are controlled. We are using super-resolution microscopy, both structured illumination- and single molecule localization-based, to elucidate the physical mechanisms behind these dynamic processes.
In the case of bacteria cell division, the control step for size homeostasis is unclear, and the relative roles of elongation and constriction and their coupling are poorly understood. Using genetic and pharmacological perturbations, we show that changing constriction rate alone can change the cell size. We also demonstrate that constriction duration compensates for elongation to allow for tighter homeostasis than either alone. We present a working model for how this may operate.
In the case of mitochondrial fission, while the cellular and molecular components implicated are known, little is known about the role of physical constraints. By comparing successful fission events with reversal events, we identify the roles of different physical parameters, such as bending energy and external pulling forces. We use existing models for membrane fission to begin to build a toy physical model for mitochondrial fission.
Conventional optical coherence tomography (OCT) employs a single illumination/detection channel to obtain 3D-data-sets of transparent or translucent samples. Our research focuses on the application of multiple channels for OCT in the field of ophthalmology, to help diagnose and monitor leading causes of blindness such as age-related macular degeneration, glaucoma or diabetic retinopathy. Using so-called multi-channel OCT, we are able to, on the one hand investigate ocular blood flow at the posterior pole of the eye (retina and choroid) by performing Doppler-OCT, and on the other hand study the directional scattering behavior of retinal tissue such as the photoreceptor layer.
A confocal microscope equipped with a pixelated detector allows for taking images with high resolution and improved SNR. This concept has become known under the name Image Scanning Microscopy(ISM). ISM can be regarded a "multi-view" instrument, because each detector pixel provides an individual confocal image. We present the combination of ISM with generalized point spread function engineering in the sense that both, excitation and detection pupil phases can be arbitrarily modified via a spatial light modulator. We demonstrate two different application fields of this "engineered ISM": acquiring 3D sample information and sensing color. For both we show how the recorded data can be processed using a maximum-likelihood joint deconvolution algorithm.
Endoscopic imaging enables diagnosis and monitoring of many diseases in vivo, inaccessible to the technical means of standard imaging modalities in terms of spatial limitations. However, in the field of biomedical-optics the integration of focusing and scanning mechanisms into small endoscopes is very challenging. We therefore evaluated an endoscopic approach that may not require any lenses or scanners by combining a fiber bundle with holography. We can demonstrate our approach with 2D- and 3D-image-data sets of a resolution target as well as images of a biological sample. The performance of different fiber bundles, each associated with individual challenges, has also been compared.
Here practical and theoretical insights on tailoring complex fluids' properties by controlling formulation and flow-field interdependency are discussed. Viscoelastic properties depend on formulation and structure of micellar aggregates at equilibrium. The interplay between hydrophobicity and charge defines the conformation of additives, when they integrate into a micelle. Well-defined microfluidics shear and extension flow-fields are designed to investigate micellar stability under flow and its impact on viscoelasticity by combining SAXS, SANS and NMR measurements. Scanning-SANS and -SAXS record flow-induced phase, while their signals provide important contrast differences for studying the impact of formulation and flow on the structure of micellar aggregates.
Quantum dots are confined semiconductor nanostructures. The confinement leads to a discrete energy spectrum, similar to the spectrum of atoms. We use the discrete energy spectrum to create single photons and cascades of photons. Quantum dots can be epitaxially grown and thus, they are an on chip photon source. They can be embedded into p-i-n junctions and can be pumped electrically, although I will focus on optical pumping in my talk. I will show, how entangled photon pairs can be created with quantum dots in different degrees of freedom.
We theoretically investigate different aspects of dynamic mesoscopic conductors with the ultimate goal of contributing to the development of quantum technologies. Key results include: demonstrating that a single-electron partitioned at a beam-splitter is entangled and therefore possibly useful for quantum computation, developing a theory of joint electron waiting times and using it to describe single-electron excitations, shedding light on the non-classicality of negative values in the full counting statistics, proposing heat engines that rely on the wave-nature of electrons and on the particle-nature of photons, and proposing a refrigerator which exhibits coherence-enhanced cooling.
The bit of a magnetic storage device is composed of hundreds of thousands of atoms. Although this number was continuously reduced with advancing miniaturization, the physical limit of one single atom per bit has remained a mere though experiment. Here we show that a single Holmium atom on magnesium oxide represents this fundamental limit. We read the single atom magnet via tunnel-magneto resistance or EPR and write its state using a current pulse from a scanning tunneling microscope. A prototypical 2-Ho bit array shows that the single atom magnets independently retain their magnetic state for hours.
We present novel model systems for catalysis that have been developed using state-of-the-art top-down nanofabrication techniques, such as extreme ultraviolet lithography and electron beam lithography, to achieve nanometer precision over particle size and its positioning. This is combined with X-ray photoemission electron microscope at the Swiss Light Source to study catalytic metal nanoparticles down to six nanometers and in-situ visualization of chemical action is done at the single nanoparticle level. Employing this strategy, a five decade old controversy around the phenomena of hydrogen spillover has been addressed. For the first time, distance dependence of hydrogen spillover has been experimentally visualized.
Jumping from the expanse of galactic scales to land in the laboratory might seem a gargantuan task. Common to both, however, is the concept of symmetry breaking and in particular the formation of topological defects. This work looks at the formation of topological defects in multiferroic hexagonal manganites whose ferroelectric behavior enables the direct imaging of these defects. I also show how this material can be used to study the Kibble-Zurek model of topological defect formation in the early universe and give quantitative insights on the number of domains formed during the spontaneous symmetry breaking phase transition.
Transition-metal oxide heterostructures are attractive for functional device applications because electronic and magnetic phases that are inaccessible in the bulk can be stabilized by epitaxial strain, confinement, charge doping, or interface effects.
We use resonant elastic x-ray scattering to investigate ordering phenomena of spin, charge and orbitals in nanoscale complex oxide multilayers. As a model system we have investigated perovskite-type RNiO3-based heterostructures (R = rare-earth ion) grown by molecular-beam epitaxy and pulsed-laser deposition on various substrates. In my talk I will present results of our studies of the layer-resolved orbital occupations, the unusual antiferromagnetic order observed in the ultra-thin limit, and the quantitative investigation of the bond-order parameter.
Perovskite rare-earth nickelates, $R$NiO$_3$, display a rich and only partially understood phase diagram, where all compounds with R from Pr to Lu undergo a metal-insulator transition (MIT) that is accompanied by a structural distortion. We use density functional theory (DFT) and its extensions (DFT+U, DFT+DMFT), combined with symmetry-based distortion mode analysis to explore the interplay between lattice distortions, magnetic order, and electronic correlation effects in rare-earth nickelates. Thereby, we want to explore the capabilities of the DFT+DMFT method to describe complex materials with coupled electronic and structural degrees of freedom.
RNiO$_3$ perovskites (R = rare earth, Tl$^{3+}$, Pb$^{3+}$ or Bi$^{3+}$) display a metal to insulator transition (MIT) at temperatures T$_{MIT}$ than increase by decreasing the lanthanide ionic radius. The electronic localization is associated to a charge disproportionation of the type 2Ni$^{3+}$ = Ni$^{3+d}$ + Ni$^{3-d}$ and with subtle structural distortions related to the Ni$^{3+d}$/Ni$^{3-d}$ charge order. Using neutron powder diffraction the lattice anomalies of PrNiO$_3$ have been re-investigated and interpreted in terms of “frozen” normal distortion modes1. We identify a new breathing mode with non-zero amplitude below T$_{MIT}$ and associate it to the charge order responsible for the MIT.
The perovskite rare-earth nickelates RNiO$_3$ are a family of transition metal oxides with strong electron correlations. They exhibit antiferromagnetic order with four Ni spins per period below a composition-dependent Néel temperature $T_\text{N}$. Despite its high relevance to theoretical claims of ferroelectricity in the magnetically ordered phase, the exact arrangement of moments is still not well established. Our recently obtained results of nuclear magnetic resonance and muon spin rotation experiments on the closely related compound TlNiO$_3$ reveal a second magnetic phase transition at $T_\text{N}^* = 202 \; \text{K}$, above $T_\text{N} = 104 \; \text{K}$. The new phase is suppressed by magnetic fields on the order of at most $1 \; \text{T}$.
Rare-earth nickelates, RNiO$_{3}$, represent an intriguing example of materials with a highly tunable metal-insulator transition (MIT) and high potential for heterostructure engineering. The $T$-dependent paramagnetic MIT observed both in the bulk and ultrathin films of RNiO$_{3}$ is almost always accompanied by a subtle crystal-structure transformation, resulting in disproportionation of Ni-O bonds. We employ recent advances in understanding the nature of the insulating phase in RNiO$_{3}$ to unravel the mechanism underlying the combined structural/metal-insulator transition. By explicitly including lattice degrees of freedom into the description we show how a peculiar electronic structure may result in stabilization of the bond-disproportionated phase and we identify two control parameters associated with the transition.
We used reflectometry and ellipsometry to investigate electronic properties of rare-earth nickelate films. We study the temperature dependence of the optical conductivity as chemical composition and strain varies close to charge and magnetic ordering temperatures.
The optical spectra show a characteristic two-peak structure when the material switches from metal to insulator that DMFT associates with a combined effect of bond disproportionation and Mott physics.
At magnetic ordering temperature, the spectral weight increases in these two peaks. Landau model with coupled charge and magnetic order parameters, indicates that charge order is required to the emergence of a long range magnetic order. Through a positive feedback, magnetic order stabilizes the charge order.
Taking advantage of the large electron escape depth of soft x-ray angle resolved photoemission spectroscopy we report measurements of the electronic structure of (111)-oriented [LaNiO3/LaMnO3] superlattices and LaNiO3 epitaxial thin films. For thin films we observe a 3D Fermi surface with an electron pocket at the Brillouin zone center and hole pockets at the zone vertices. Superlattices with thick nickelate layers present a similar electronic structure. However, as the thickness of the LaNiO3 is reduced to 7 monolayers the superlattices become insulating. These heterostructures do not show a marked redistribution of spectral weight in momentum space but exhibit a pseudogap of ≈ 50 meV. [APL Materials 5, 016101 (2017)]
The process of electron-positron pair production in oscillating electric fields is investigated in the nonperturbative threshold regime.
Similarities between atomic ionization and pair production are pointed out and an effective mass model is introduced.
Accurate numerical solutions of the quantum kinetic theory for various observables are presented and analyzed in terms of the effective mass model.
The presentation will summarize scope and status of the International Future Circular Collider Study. Machine concepts and parameters will be presented together with essential technical components to be developed. Key elements are superconducting accelerator-dipole magnets with a field of 16 T for the hadron collider and high-power, high-efficiency RF systems for the lepton collider. In addition the unprecedented beam power presents special challenges for the hadron collider for all aspects of beam handling and machine protection. The status of the infrastructure study will also be summarized and the initial considerations for experiments will be presented.
The Advanced Proton Driven Plasma Wakefield Acceleration Experiment (AWAKE) aims at studying plasma wakefield generation and electron acceleration driven by proton bunches. It is a proof-of-principle R&D experiment at CERN and the world's first proton driven PWFA experiment. The AWAKE experiment uses the 400GeV/c proton beam bunches from the SPS. The first experiments started end 2016 and focus on the self-modulation instability of the long (rms ~12cm) proton bunch in the plasma. Later, in 2017/2018, low energy (~15MeV) electrons will be externally injected to probe the wake-fields and be accelerated beyond 1GeV. First results are shown. A summary of the AWAKE design and construction status will be presented.
In this presentation I will provide a concise overview of the main physics analyses that are planned to be carried out with thevery large data set delivered during the High-Luminosity LHC phase (HL-LHC). Some particular physics channels will be highlighted.
The European Strategy Forum on Research Infrastructures (ESFRI) pursues various research approaches in the field of particles and cosmology. In this talk, I will present precise symmetry tests of various kinds, which are coming within reach with ESFRI Landmarks and new neutron sources. In focus are searches for possible deviations from the Standard Model (SM) of particle physics with cold and ultra-cold neutrons. Next, we present a novel direct search strategy with neutrons in the gravity potential of the earth. The aim is to test the law of gravitation with a quantum interference technique, providing constraints on dark matter and dark energy.
The new X-Ray Free Electron Laser (SwissFEL) facility at PSI has produced its first FEL light at 4.1 nm and will deliver 20 fsec pulses of coherent x-rays in the wavelength range 0.1 to 7 nm, with extremely high peak brightness. These characteristics will provide opportunities for new experiments in chemistry, solid state physics, biology and materials science. The Aramis hard x-ray FEL branch will begin normal user operation in 2018 with two dedicated end-stations. The Alvra end-station is focused on using time resolved x-ray spectroscopy (XAS/XES) to investigate femtosecond chemical processes and time-resolved x-ray diffraction for serial femtosecond crystallography (SFX) experiments on proteins. The Bernina end-station is designed for femtosecond time-resolved pump-probe hard x-ray diffraction and scattering experiments in condensed matter systems. The Athos soft x-ray FEL branch is in the early phase of construction and should provide its first FEL light for experiments in 2020. After a brief status report, the presentation will focus on novel applications, the description of the fundamental aspects of the planned facility with an emphasis on the photonics part of the project.
Time-resolved X-ray spectroscopy is a versatile tool for investigating both electronic and structural dynamics in functional chemical systems. By measuring both the X-ray absorption and X-ray emission signals simultaneously we obtain information on both the occupied and unoccupied electronic states of the sample, as well as structural information from both the near-edge and Extended X-ray Absorption Fine Structure (EXAFS) regions of the absorption spectrum. When combined with X-ray scattering techniques, which provide structural information on the system and its interaction with the environment, we can obtain unparalleled details on the ultrafast dynamics of both energy flow and structural changes. In this presentation, I will show how we have developed these techniques at the Swiss Light Source and other X-ray facilities, and applied them to investigate ultrafast dynamics in photo-excited systems. I will present several examples of the kind of information that can be obtained on a large variety of samples, ranging from photoactive proteins in solution through to colloidal suspensions of semiconductor nanoparticles. I will conclude with a brief overview of the types of experiments we anticipate being able to perform at SwissFEL in the coming years.
Ultra-short, ultra-bright X-ray pulses from Free Electron Lasers are a viable tool for observing diffraction from two-dimensional (2D) crystals, unlike synchrotron-based data collection, extending the possibilities of structural determinations in membrane proteins.
Using serial diffraction frames from bacteriorhodopsin 2D crystals we extended the resolution limit of zero-tilt data to 4 A (detector-limited) by summing equivalent portions of images, and developed a method to reconstruct diffraction intensities along Bragg lines, from which structural information can be gained.
Using these methods a data collection strategy (100'000 - 200'000 images at high tilt angles) allowing to detect structural changes in the length-scale of a few A in a pump-probe configuration can be envisaged.
SwissFEL, like other SASE-based x-ray FEL facilities, requires the monitoring of the photon spectrum (photon energy and intensity) on a shot-to-shot basis for machine optimization and for experiments. In order to cover the Hard X-ray range variations (4-15keV) for the Aramis beamline, the Photon Single Shot Spectrometer has been designed to measure the spectrum with high resolution over the bandwidth of the SASE FEL beams. Additionally, a new idea and first results of a proof-of-principle experiment for an online device in Tender X-ray regime (2-4keV) will be shown and discussed. The concept is based on dispersive von-Hamos geometry composed with a scattering sample to look at the elastic scattering spectrum.
ACHIP is an international collaboration, funded by the Gordon and Betty Moore Foundation, whose goal is to demonstrate that laser-driven accelerator on a chip can be integrated to fully build an accelerator based on dielectric structures.
PSI will provide access to the high brightness electron beam of SwissFEL to test structures, approaches and methods towards achieving the final goal of the project.
In this contribution we describe the design of the interaction chamber, in collaboration with EPFL, to perform the proof-of-principle experiments. We will present the positioning system for the samples, the magnets focussing the beam to sub-micrometer dimensions and the diagnostics to measure beam properties at the interaction point.
The next hard X-ray line (2025-2029) at SwissFEL, Porthos, is planned to further extend the photon energy of Aramis, reaching wavelength down to 0.03 nm. Harmonic lasing and inter-undulator chicanes will be implemented to meet this target. Nevertheless the undulator period length must decrease to 10 mm while the K value has to increase to 2.4 with a vacuum gap above 4 mm. These parameters cannot be achieved with conventional technology, neither with advanced permanent magnet cryogenic undulators: it requires the use of superconductors. An overview of this technology will be given, focused on recent Nb3Sn experimental results but alternative approach, like bulk HTS superconductor, will also be discussed.
We will discuss the initial value problem given by the incompressible Navier–Stokes equations in $\mathbb{R}^3$. All known well-posedness results for this problem are in the perturbative regime and in this talk we will show numerically that the problem is ill-posed outside the perturbation regime. More precisely, we numerically construct two different solutions having the same initial datum in borderline spaces.
For $N$ hard-core bosons on an arbitrary lattice with $d$ sites and independent of additional interaction terms we prove that the hard-core constraint itself already enforces a universal upper bound on the Bose-Einstein condensate given by $N_{max}=(N/d)(d-N+1)$. This bound can only be attained for one-particle states $|\varphi\rangle$ with equal amplitudes with respect to the hard-core basis (sites) and when the corresponding $N$-particle state $|\Psi\rangle$ is maximally delocalized. This result is generalized to the maximum condensate possible within a given sublattice. We observe that such maximal local condensation is only possible if the mode entanglement between the sublattice and its complement is minimal.
I investigate the critical dynamics of a periodically driven Bose gas. The inclusion of dissipation enables the system to reach a far-from-equilibrium steady state where the periodic drive plays an essential role. Combining the Renormalization Group (RG) and Floquet formalisms, I describe the steady state by allowing for an arbitrary number of Floquet modes to be occupied. In practice, this means that the coupling constants become periodic functions of time as they are renormalized. As a first step, the RG flow equations are computed at one-loop. They are then linearised at the (Wilson-Fisher) equilibrium fixed point and an infinite number of relevant directions emerge because of the non-equilibrium drive.
The fermionic exchange symmetry does not only imply Pauli's exclusion principle but even further constraints on fermionic occupation numbers. In particular, generalized Pauli constraints become relevant whenever they are (approximately) saturated. We explore the occurrence of such (quasi)pinning through a comprehensive analysis of an analytically solvable model (Harmonium). By analysing the strength of quasipinning as function of the particle number, coupling strength, spatial dimension and degree of spin polarization we reveal the mechanism behind it. It is the conflict of energy minimization and fermionic exchange symmetry. Consequently, our results suggest the existence of a microscopic Pauli pressure which forces the system into an approximate saturation of the generalized Pauli constraints.
We study the time evolution of 2-point-functions and entanglement-entropy in anisotropic and time dependent $\mathcal{N}=4$ super-Yang-Mills-theory in the large $N$ and large 't Hooft-coupling limit using AdS/CFT.
On the gravity side this amounts to calculating geodesics and extremal surfaces in the background of two colliding gravitational shockwaves, which we do numerically.
Discriminating between three classes of initial conditions corresponding to wide, intermediate and narrow shockwaves, we show that the behavior of the non-local observables is different.
Another interesting result is that 2-point-functions can be sensitive to the inside of a black hole apparent horizon while we could not find such dependence for the entanglement-entropy.
This talk is based on arXiv:hep-th/1609.03676.
Understanding electron correlations is nowadays crucial for advances in quantum electronics and nano-sciences. Quantum Monte-Carlo simulation (QMCS) methods, being highly time consuming, are limited to yield selective data points only. We here employ a Hyper-Netted-Chain-theory based approach to compute the spin-resolved pair distribution functions and static structure factors of the two-dimensional, partially spin-polarised electron liquid. Compared to QMCS, remarkable accuracy is achieved in a fraction of time. For a broad range of densities and polarisations we apply this to investigate how increasing the layer-width alters the correlations.
We consider Gaussian fermionic states and their entanglement properties. Among continuous variable systems Gaussian states stand out prominently, because of their simple and elegant mathematical description in terms of first and second order correlations. Moreover, the subclass of Gaussian fermionic states has the distinguished feature, that they can be mapped onto systems consisting of qubits via the so-called Jordan-Wigner transformation. We characterize possible transformations of (pure) single- and multimode states via Gaussian (fermionic) local operations assisted by classical communication. Thus, also the most useful states in this context, i.e. states in the maximally entangled set, are determined. Furthermore, their entanglement is quantified and qualified by computing operational entanglement measures.
We study 1D insulators obeying a chiral symmetry in the single-particle picture where the Fermi energy is assumed to lie within a mobility gap. Topological invariants are defined for infinite (bulk) or half-infinite (edge) systems, and it is shown that for a given bulk system with N.N. hopping, the invariant is equal to the induced-edge-system's invariant. We also give a new formulation of the topological invariant in terms of the Lyapunov exponents of the system, which sheds light on the conditions for topological phase transition extending to the mobility gap regime. Finally we give a proof of complete dynamical localization for our model via Furstenberg's theorem and the fractional moments method, which justifies the deterministic assumptions we make.
The possible compatibility of density matrices for single-party subsystems is described by linear constraints on their respective spectra. Whenever some of those quantum marginal constraints are saturated, the total quantum state has a specific, simplified structure. We prove that these remarkable global implications of extremal local information are stable, i.e. they hold approximately for spectra close to the boundary of the allowed region. Application of this general result to fermionic quantum systems allows us to characterize natural extensions of the Hartree-Fock ansatz and to quantify their accuracy by resorting to one-particle information, only.
The Start-Up Ecosystem of Switzerland consists of a wide variety of cantonal, federal and private initiatives. This short introduction to the topic will provide an overview of the most relevant available Startup programs, co-working spaces, accelerators and support system, thus laying the ground for the present Startuper’s experiences in their respective pitches and the following panel discussion. This may allow the identification of Start-Up Challenges and Experiences as well as some best practice and real world advice.
IRsweep was founded as a spin-off of ETH Zürich in 2014 with the mission to make frequency comb spectroscopy available to field applications. While a solid technology is the foundation of IRsweep, much more is required to turn it into a successful hardware product and an account of the journey from experiments to a working product will be given – including some detours on the way.
FEMTOprint SA is a Swiss high-tech company specialised in manufacturing 3D microdevices out of glass and other transparent materials. Founded in 2013, it is a spinoff of a European Project financed by Factories of the Future and FP7, which developed the innovative process FEMTOPRINT®, able to produce precise freeform 3D microdevices integrating optical, fluidic and mechanical functionalities in a monolith.
This pitch will give you more than a clue on this disruptive technology and the wide range of challenging applications covered, but also an insight into the technical and strategic progresses made from the very beginning until today by the Start-up.
Research on macroscopic quantum phenomena at the University of Vienna has resulted in the development of a new optical coating technology with unprecedented performance. The spin-off company Crystalline Mirror Solutions has taken this technology to the market. In a nutshell, substrate-transferred crystalline coatings allow to exploit the unique properties of single-crystal semiconductor coatings for high-end laser optics applications. They exhibit order of magnitude improvements in mechanical loss (i.e. thermal noise), thermal conductivity, and potentially in absorption losses in the mid-infrared spectral region. Application examples include ultra- stable lasers, optical precision measurements, high-power SESAMs, and high-finesse MIR optical cavities in the fingerprint region for optical trace gas sensing.
The Center for Rapid Innovation is the Fablab of the business incubator Werkstätte Wattens has been very much inspired by the Fab Central at MIT’s Media Lab. As a high technology digital fabrication laboratory, our goal is to sustainable enable students, start-ups, established companies as well as common people (makers) alike an access to state of the art rapid prototyping technology.
Cases indicate the importance of building up an innovative ecosystem, an open environment, a place for experimentation and failing fast, and a singularity-like spot that attracts highly talented people to explore technologies – from prototyping over proof of concept to pilot series. We discuss the required tools and processes for such a successful transformation and suggest Fablabs as a well suited environment to enable the spiral innovation process needed for technology driven innovation.
Mammalian gene transcription occurs stochastically in short bursts interspersed by silent intervals. However, the underlying processes and consequences on fluctuations in gene products are poorly understood. In our lab we combine time-lapse imaging of a short-lived transcriptional reporter with stochastic modeling to quantitatively characterize transcriptional bursting. While bursting kinetics is generally gene-specific, we found that endogenous gene promoters typically exhibit refractory periods lasting about one hour before turning on again. Recently, we extended our models to identify minimal promoter cycles, which inform on the number and durations of rate-limiting steps responsible for refractory periods. We found that the structure of promoter cycles was promoter specific and independent of genomic location. Typically, five rate-limiting steps underlie the silent periods of endogenous promoters, while minimal synthetic promoters exhibit only one. In addition, certain promoter architectures, notably ones containing TATA boxes, show simplified two-state promoter cycles associated with increased intrinsic noise.
In addition, we observed large variability in burst sizes and frequencies between genes. To better understand the regulation of burst size and frequency, we followed the expression level of a Bmal1 transgene, a core circadian clock promoter, throughout the circadian cycle and inserted at different genomic loci. We observed both in living and fixed cells that the circadian phase predominantly modulated the burst frequency while the integration site mostly affected the burst size. Furthermore, we found that the clock-dependent modulation of burst frequency was associated with variations in histone acetylation levels. Additional experiments on other genes suggest correlation between acetylation levels and burst frequency likely may be a general feature of gene transcription. Thus, we begin to understand how gene expression modulation can occur both by tuning the burst size and frequency, involving different molecular mechanisms.
Visco-elastic sheets have unique mechanical properties when it comes to understanding their deformation and topological changes. In the lab, we have studied the deformation of two biological visco-elastic sheets which have different spatial scales and characteristic visco-elastic times: lipid membranes, which are curved into membrane carriers in membrane transport, and epithelia, or cell monolayers, which curve ad bend to generate organs such as the brain or the gut. We have found that a protein complex, called ESCRT-III, accumulates elastic stress while polymerizing as a spiral at the surface of lipid membranes, while an epithelium accumulate stress when encapsulated in an alginate hollow sphere, because of its proliferation. In both cases, the lipid membrane and the epithelium is deformed concomitantly to the release of the elastic stress, in a buckling process. I will discuss the similarities and the differences of this buckling mechanism observed at different biological scales.
Collective behaviour is found in wide variety of life-forms, from bacteria to humans, and it is an intriguing phenomenon with implications ranging from ecology and sociology to agriculture and artificial intelligence. I will discuss how tools from physics and machine learning can shed light on the origins and dynamics of collective motion. Specifically, I will present a model in terms of learning agents, which learn by themselves how to behave in different environments and, in the process, can develop strategies like alignment and collective sensing.
The use of proton therapy for cancer treatment shows a growing trend.
To direct the proton beam from all directions to the tumor in the patient, a rotatable gantry is used.
In this work we present the design of a superconducting bending magnet section for future light and compact iso-centric gantries. The coils will be wound with Nb3Sn Rutherford cables. Following the choice of a suitable superconducting strand, we estimate the AC losses during the energy sweeps, the expected coils heating in operation and the design of the cooling system as well as of the mechanical support structure. Considerations about the quench protection scheme are also presented.
Sharpened glass fiber – made probes attached to a quartz tuning fork exploiting the shear force–based feedback is the most popular in the field of SNOM. The use of tapping mode feedback could be preferable. Here we report such an approach realized via bent fiber probes. Detailed analysis of the vibration mode shows that an extreme caution is needed for the realization truly tapping mode. Bent probes were attached to the TF in double resonance conditions enabling to achieve very large quality factor. The performance of these probes is demonstrated. The next step is the testing of this probes in liquid.
Within the SAFIR collaboration, a high-rate PET-insert compatible with a pre-clinical 7T-MRI scanner is being developed. The SAFIR insert aims at enabling truly real-time dynamic tracer studies with unprecedented high temporal resolution of ~5s. The insert comprises 2.1x2.1x12mm3 crystals one-to-one coupled to SiPM arrays and fast-readout ASICs. At 500MBq activity, the detector is required to be capable of acquiring 40kHz-hits for each ~15000 readout channel. The energy and the coincidence time resolution will be < ~20% and <300ps, respectively. The scanner will have ~2mm-FWHM spatial resolution. This presentation will summarize the concept, current status, and perspectives of the SAFIR insert.
TbMnO$_3$ is a well-studied low-temperature multiferroic. Below 41 K the magnetic system orders antiferromagnetically into a spin density wave. Upon further cooling, below 27 K, the magnetic order changes to cycloidal and a ferroelectric polarization arises.
We present our results on photoinduced demagnetization dynamics in TbMnO$_3$, following excitation at 1.55 eV and 3 eV photon energies. The magnetic and orbital orders are tracked via the (0 $q$ 0) and (0 $2q$ 0) reflections, respectively, using polarization dependent resonant X-ray diffraction at the Mn $L_2$ edge. The timescales and pathways of the transition between the multiferroic and the high temperature phase will be discussed.
Complex oxide thin films and heterostructures exhibit a wide variety of interesting functionalities that are generally determined by numerous factors.
Here, we investigate the effects of epitaxial strain, dimensional confinement, as well as interface and surface effects on the electronic properties of the correlated metal CaVO$_3$, using a combination of density functional theory (DFT) and dynamical mean-field theory (DMFT). We show that tensile epitaxial strain can induce a metal-insulator transition in CaVO$_3$, and we demonstrate that this strain effect cooperates with a similar tendency originating from the finite thickness of the film, consistent with recent experimental observations. Furthermore, we also address the influence of the substrate-film interface in CaVO$_3$/LaAlO$_3$ heterostructures.
The control of the oxygen vacancies content in magnetoelectric oxides opens new routes to induce unexpected properties in strained thin films. Here we show experimental evidence for the increase of the oxygen-vacancy content upon increasing tensile epitaxial strain in multiferroic SrMnO3 thin films. Furthermore, a novel dependence of the oxygen stoichiometry on the film thickness has been found, allowing us to control the concentration of these defects by both the applied strain and film thickness. We analyze the effect of the oxygen-vacancy content on the ferroic properties of strained SrMnO3 films focusing on the generation of a flexoelectric component that rotates the in-plane <110> ferroelectric polarization.
Multiferroism can originate from the breaking of inversion symmetry caused by magnetic-spiral order. It usually arises due to competing magnetic exchange interactions that differ by their range and sign, and thus occurs at low temperatures. I present a mechanism that works at much higher temperatures. It relies on frustrating bonds randomly introduced along a single crystallographic direction, as found in a realistic model of YBaCuFeO5, where spiral order at high temperatures was indeed reported. We predict a correlation between the ordering temperature and the spiral wavevector. We show that spin orbit coupling at impurities induces a tilting of the easy plane, which ensures that spiral order couples to electric polarization.
The sensitivity of the Jeff = 1/2 state of Sr2IrO4 to local coordination and structural distortions suggests epitaxial strain as an ideal route for manipulating this exotic ground state. As recently demonstrated, oxygen K-edge RIXS is capable to capture magnetic excitations in 5d-oxides [1]. From O K-edge RIXS on roughly 20-nm thick Sr2IrO4 films we observed the low-energy elementary excitations encompassing single magnons, bimagnons and spin-orbital excitations and their dispersion relations. In this talk, I will present a direct observation of the evolution of these low-energy quasiparticle excitations and spin dynamics upon epitaxial strain in the Jeff = ½ Mott insulator Sr2IrO4.
[1] X. Lu et al, manuscript submitted
In 5-d transition metal oxides, spin-orbit coupling becomes sizable and its interplay with e.g. the Coulomb interaction has led to the observation of exciting novel ground states. We report here on NaOsO3, which has been proposed to be the first realization of a Slater insulator i.e. a system in which a metal-insulator transition is driven only by antiferromagnetic correlation. We employed Resonant X-ray Diffraction to elucidate the nature of the metal-insulator transition. By a careful study of forbidden reflections, we can exclude the presence of a structural crystallographic change at the phase transition. In addition, we observe an anomaly below the Neel temperature that is indicative of the Slater scenario.
Within the talk I will review our activity on spintronic applications which is done in close cooperation with the industrial partner Infineon AG. The advantage of topological charged vortex structure for sensor application for low noise speed sensors will be reported that will be commercialized by Infineon for ABS systems in cars in 2018.
As a second example, we will review the potential of skyrmion based racetrack structures. We will report the effect of structural pinning sites in order to stabilize magnetic skyrmion position in order to store stable bits. The energy barrier for annihilation of skyrmion at the boundary will be compared with the energy barriers to overcome these pinning site. It is shown that skyrmions can be more effectively pinned than protected from annihilation via boundaries.
Perpendicularly magnetized nanowires exhibit distinct domain wall types depending on the geometry. Wide wires contain Bloch walls, narrow wires Néel walls. Here, the transition region is investigated by direct imaging of the wall structure using high-resolution spin-polarized scanning electron microscopy. An achiral wall type is discovered whose in-plane magnetic moment angle is intermediate between the one of Bloch and Néel walls which is unpredicted by established theoretical models. With the help of micromagnetic simulations, we find that the transition via this intermediate wall should occur in any perpendicularly magnetized material provided the wire width is chosen accordingly.
We study theoretically the triangular-lattice, Ising antiferromagnet with long-range dipolar interactions, inspired by its realisation in nano-magnet arrays. We show that a classical spin-liquid regime exists above a low-temperature ordered phase, and explore how the nature of the spin liquid can be altered by a small lattice deformation. Deforming the lattice also tunes the nature of the transition from first order to Kasteleyn, via an unusual tricritical point. We show that the behaviour can be naturally explained in terms of a set of interacting strings, and this leads to an analogy with 1D quantum systems of spinless fermions.
Quasistatic studies on artificial quasicrystals reported exotic properties such as knee anomalies in the magnetic hysteresis. Spin wave resonances may help to further understand their exotic properties.
We fabricated interconnected networks of nanobars (810 nm long, 130 nm wide) from 25 nm thick Permalloy and arranged them on Penrose P2, P3, and Ammann quasicrystal lattices. Performing angular dependent broadband spectroscopy in the GHz frequency regime we observed systematic and reproducible spin wave resonances in the switching regime. Combined with micromagnetic simulations and X-ray photoemission electron microscopy we discuss our experimental results in view of reprogrammable magnonic devices. *Research supported by SNF (#163016) and DFG (TRR80-F7).
Enhanced magnetism in 3d transition metal nanoparticles is of great interest for applications and for our fundamental understanding of nanomagnetism. However, despite considerable research efforts, the origin of anomalous magnetic properties in nanoparticles, such as enhanced magnetic anisotropy, are still poorly understood. Here, we combine X-ray photo-emission electron microscopy (X-PEEM) with high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) in order to correlate magnetism and microstructure of individual nanoparticles. Our data suggest that the magnetism of cobalt nanoparticles is determined by competing shape, surface, and structural contributions. Further, we find that this competition can easily mask the commonly expected size dependence of nanoparticles magnetic properties such as magnetic energy barriers.
Antiferromagnetic materials play an important role in modern spintronics devices. While the properties of antiferromagnetic bulk materials are often well investigated, much less is known about their properties at the nanoscale. Here, we use X-ray photo-emission electron microscopy (X-PEEM) together with X-ray magnetic linear dichroism to study the magnetism of individual goethite nanoparticles. The X-PEEM data are combined with scanning electron microscopy to correlate the magnetic properties of the nanoparticles with their actual morphology. Our data indicate that goethite nanoparticles are antiferromagnetically ordered at room temperature, similar to the respective bulk, however, a preferred magnetization axis is not found.
Current-induced spin-orbit torques (SOTs) represent one of the most effective ways to manipulate the magnetization in spintronic devices. The orthogonal torque-magnetization geometry and the large domain wall velocities inherent to materials with strong spin-orbit coupling make SOTs appealing for fast switching applications in nonvolatile memory and logic units. Here, we report the first direct observation of SOT-driven magnetization dynamics in Pt/Co/AlOx dots during current pulse injection. Time-resolved x-ray images with 25 nm spatial and 100 ps temporal resolution reveal that switching is achieved by fast nucleation of an inverted domain at the edge of the dot and propagation of a tilted domain wall across the dot.
The large data samples at the High-Luminosity LHC will enable precise measurements of the Higgs boson and other Standard Model particles, as well as searches for new phenomena as predicted by supersymmetry and extra dimension theories. To cope with the large radiation doses and high pileup expected at the High-Luminosity HLC, the current ATLAS Inner Detector will be replaced with a new all-silicon Inner Tracker.
The tracking performance of a candidate ATLAS Inner Tracker layout with a wide acceptance of $|\eta|<4.0$, employing a five-layers inclined pixel barrel surrounded by a four barrel layer strip detector, is evaluated. System aspects for the pixel system will also be described.
A novel higher-level flavour tagging algorithm called DL1 has been developed using a neural network at the ATLAS experiment at the CERN Large Hadron Collider. We have investigated the potential of Deep Learning in flavour tagging using higher-level inputs from lower-level physics-motivated taggers. The DL1 studies presented show that the obtained neural network improves discrimination of b-jets against both light-flavoured-jets and c-jets, and also provides a novel c-tagging possibility, which also makes it a highly flexible tagger. The DL1 tagger is described and a detailed set of performance plots presented, obtained from simulated ttbar events at $\sqrt{s}$=13 TeV and the Run-2 data taking conditions where this tagger will be applied.
Identification of hadronically-decaying W bosons and top quarks using high-level features as input to deep neural networks and boosted decision trees is investigated. The use of machine learning techniques is found to improve the background rejection with respect to simple reference single jet substructure and mass taggers.
The spectrum of differential observables related to Higgs boson production is a sensitive probe to new physics. At the LHC, Higgs production is dominated by gluon fusion, for which loop contributions from new physics may manifest in the shape of differential observables. With the millions of produced Higgs bosons at the High Luminosity LHC, limits on Higgs couplings from differential observables are expected to be competitive with direct probes. Limits on Higgs couplings are set using recent data obtained with the CMS detector from multiple decay channels.
Studies of semileptonic decays at LHCb cover a wide-range of possible measurements: cross-sections, lifetimes, mixing and CP violation, CKM matrix elements, tests of lepton universality... Thanks to their large statistics, semileptonic decays allow for ultimate precision measurements, assuming systematic uncertainties can be kept under control.
I will present here a brief selection of the latest results on the topic.
The violation of CP symmetry is well established nowadays in the K and B mesons sectors. However, CPV has not been observed in the baryonic sector. Charmless b-baryon decays represent a promising opportunity in this respect since their amplitudes receive contributions from tree level diagrams where the CKM element Vub appears. In addition, these decays are sensitive to possible physics beyond the SM, since they receive relevant contributions also from penguin topologies. We present the most recent measurements of charmless b-baryon decays performed by LHCb, including branching ratios and T-odd correlations.
Measurements of CP violation and flavour oscillations of neutral $B$ mesons require the knowledge of the meson flavour at the production time.
Flavour tagging algorithms in the LHCb experiment, despite the challenging, harsh environment due to $pp$ collisions, allow to perform such measurements with very high precision.
Recent examples feature world-leading results in the determination of the CKM angle $2\beta_s$ and the weak phase difference $\phi_s$, as well as measurements of the CKM angle $\gamma$.
Flavour tagging algorithms exploit the correlations between the $B$ meson flavour and different features of the event, and rely on advanced multivariate analysis techniques.
The details of these algorithms are presented, together with their performances.
LHCb has the largest samples of two-body charmed hadron decays collected by any experiment to date. These samples are yielding some of the world's most precise measurements of neutral $D$-meson mixing parameters and most sensitive searches for indirect $C\!P$ violation in charm decays. The current world best time-dependent $C\!P$ asymmetries in the decay rates of the singly Cabibbo-suppressed decays $D^0 \to K^+K^-$ and $D^0 \to \pi^+\pi^-$ are presented.
Differential cross section measurements of the Higgs boson at the LHC are important tools to study possible signs of new physics beyond the Standard Model. A common way to compare the results of the measurements with theory predictions is to unfold the measured spectra to particle level.
An alternative approach, developed in the context of the CMS measurement of the $\mathrm{H} \rightarrow \gamma \gamma$ differential cross sections, is presented. In this approach, MVA methods are used to model the response of the detector differentially as a function of several input variables.
Over the course of LHC Run 2, physics at the LHC has been shifting gradually into a high-luminosity mode, where the rate of data-accumulation outweighs any advances in the energy frontier. Augmented luminosity comes at the cost of increased pileup. Already a challenge, pileup will be the foremost problem for analysis at the HL-LHC, necessitating new strategies in detector design and event reconstruction. This presentation will review recent and impending advances in the ATLAS experiment's offline and trigger jet reconstruction such as particle flow and pileup reduction using hardware tracking, and their impact on hadronic physics.
Jet substructure techniques play a critical role in ATLAS in searches for new physics, are increasingly important in measurements of the Standard Model, and are being utilized in the trigger. To date, ATLAS has mostly focused on the use of calorimeter-based jet substructure, which works well for jets initiated by particles with low to moderate boost, but which lacks the angular resolution needed to resolve the desired substructure in the highly-boosted regime.
We present a novel approach designed to mitigate the calorimeter angular resolution limitations at a fundamental level, resulting in new objects. This approach provides superior performance compared to past methods for both jet mass and substructure variables.
The LHC will be upgraded to a High Luminosity running mode around 2025. In accordance with this machine upgrade, the current Inner Detector of the ATLAS experiment will be replaced with a new all-silicon Inner Tracker (ITk) comprising of pixel and micro-strip silicon sensors. A candidate technology for the outer pixel layers of ITk is a new radiation hard monolithic pixel sensor, based on High Voltage CMOS (HV-CMOS) technology, allowing for the pixel electronics to be embedded in the silicon sensor itself. The characterisation of full demonstrator sensors produced in both the 350nm and 180nm process will be presented, as part of an overview of a designated test beam campaign.
The large amount of data collected by the ATLAS experiment in the coming years might open the door to a totally new domain of particle physics. However, the increased luminosity of the High-Luminosity LHC (HL-LHC) will result not only in an enhanced access to new physics, but also in an extreme contamination from multiple hadronic interactions commonly known as pileup. This contamination will become critical for the ATLAS data acquisition system which will have to deal with increased background rates and higher energy thresholds. This presentation aims to review the current status of the ATLAS Phase-II trigger upgrade, with a particular focus on online pileup suppression using online tracking techniques.
With ever increasing luminosity at the LHC, optimum online data selection is getting more and more important. While in the case of some experiments (LHCb and ALICE) this task is being completely transferred to computer farms, the others - ATLAS and CMS - will not be able to do this in the medium-term future for technological, detector-related reasons. Therefore, these experiments pursue the complementary approach of migrating more and more of the offline and high-level trigger intelligence into the trigger electronics. The presentation will illustrate how the Level-1 Trigger of the CMS experiment and in particular its concluding stage, the so-called “Global Trigger”, take up this challenge.
The $\bar{\text P}$ANDA experiment at FAIR will perform high precision hardron physics experiments in the strange and charm quark sector using cooled beams of antiprotons at high luminosity with 1.5 GeV/c to 15 GeV/c momentum.
For the identification of low momentum charged particles with extreme accuracy the barrel time-of-flight (TOF) detector is one of the key components of $\bar{\text P}$ANDA. The barrel detector has ~1 m diameter, covering 22-140 degree lab angle. A single counter intrinsic time resolution of ~60 ps has been reached.
In this talk I will present optimization of operational conditions and time resolution.
The beam gas vertex detector (BGV) is a beam profile monitor at the Large Hadron Collider (LHC). It is based on a technique that was pioneered in the LHCb experiment where charged particles produced in inelastic beam-gas interactions are used to reconstruct beam-gas vertices and obtain the transverse beam shape. This non-destructive method allows the measurement of additional beam properties, like position, tilt and relative bunch populations, throughout the complete LHC cycle. A BGV demonstrator device using scintillating fibre detectors read out with silicon photomultipliers was installed in LHC Ring 2 in 2015. We present an overview of the project and report first results from the commissioning in 2016.
DECTRIS, founded 2006 as a spin-off from the PSI, is a Swiss company spezializing in high-end X-ray detectors. The company's mission is to bring single photon counting technology originally developed for the LHC to users in science, medicine and industry.
This talk is both a look back and a look ahead: what did it take to become the widely recognized leader for X-ray detectors for synchrotrons and laboratories, and what will it take to capture the markets in X-ray imaging and electron microscopy in the coming decade?
Over 7 million people die each year worldwide because of air pollution, mainly due to the use of fossil fuels. About 80 % of energy consumption is in cities where space is limited and esthetics are important. Buildings tend to be high and there is not enough roof-top space for classic PV technologies to produce sufficient energy. g2e’s product, a transparent colored glass producing energy, is set to address this challenge. This product turns each high building into a potentiel power plant. This is game-changing technology based on the inventions of Professor Graetzel of EPFL and industrialized by g2e.
New technologies are needed to still our never ending hunger for energy in a sustainable way. TwingTec develops a new wind energy technology which can reach the strong winds at higher altitudes using only a fraction of the material of a wind turbine. The presentation will give an overview of our technology and some inputs on why I ended up as a physicist to leave the world of science to enter the stormy waters of a startup in order to strive with a dedicated team for disruptive products.
The 20th century has seen a rise in data-driven methods in most sectors of education. Recently, libraries like Wikipedia, have brought always available content. Why memorize dates and other data if it is ever accessible? Waltzing Atoms is an EdTech-Startup from Vienna that playfully sparks the enthusiasm for science in young people. The software tool targets especially those students who consider chemical content currently as too abstract. Tools like Waltzing Atoms represent a fundamental change to the data-driven approach: Instead of listing data, an investigation with unknown result brings back motivation to science education.
Moderation: Paul Duvoisin
Use public transport. Details will follow.
You have to register in advance for the dinner, using the Conference Registration form. On-site registration is NOT possible.
With regard to the development of approaches to realize “Designer Solids” by programmed assembly of building units taken form libraries, recently metal-organic frameworks (MOFs) have attracted a huge interest. Here, we will focus on MOF-based electrochemical [1,2], photoelectrochemical [3] and photovoltaic devices [4,5]. Internal interfaces in MOF heterostructures are also of interest with regard to photon-upconversion [6] and can be used for the crosslinking of sandwiched, reactive monomers [7]. Since the fabrication of reliable and reproducible contacts to MOF-materials represent a major challenge, we have developed a layer-by-layer (lbl) deposition method to produce well-defined, highly oriented and monolithic MOF thin films on a number of different substrates.
[1] A. Dragässer, O. Shekhah, O. Zybaylo, C. Shen, M. Buck, Ch. Wöll, D. Schlettwein Chem. Comm., 48, 663 (2012)
[2] J. Liu, M. Paradinas, L. Heinke, M. Buck, C. Ocal, V. Mugnaini, Ch. Wöll Chem.Electro.Chem., 3, 713 (2016)
[3] Lu Ye, J. Liu, Y. Gao, Ch. Gong, M. Addicoat, Th. Heine, Ch. Wöll, L. Sun
J. Mater. Chem. A, 4, 15320, (2016)
[4] J. Liu, W. Zhou, J. Liu, I. Howard, G. Kilibarda, S. Schlabach, D. Coupry, M. Addicoat, S. Yoneda, Y. Tsutsui, T. Sakurai, S. Seki, Zh. Wang, P. Lindemann, E. Redel, Th. Heine, Ch. Wöll, Angew. Chemie Intl. Ed., 54, 7441 (2015)
[5] J. Liu, W. Zhou, J. Liu, Y. Fujimori, T. Higashino, H. Imahori, X. Jiang, J. Zhao, T. Sakurai, Y. Hattori, W. Matsuda, Shu Seki, S. K. Garlapati, S. Dasgupta, E. Redel, L. Sun, Ch. Wöll, Journal of Mat. Chem. A, 4, 12739 (2016)
[6] M. Oldenburg, A. Turshatov, D. Busko, S. Wollgarten, M. Adams, N. Baroni, A. Welle, E. Redel, Ch. Wöll, B. S. Richards, I. A. Howard, Adv. Mater., 28, 8477 (2016)
[7] Z. Wang, A. Blaszczyk, O.Fuhr, S.Heissler, C.Wöll, M.Mayor, Nat. Comm., 8, 14442 (2017)
[8] Jin-L. Zhuang, A. Terfort, C. Wöll, Coordination Chemistry Reviews, 307, 391, (2016)
[9] J. Liu, T. Wächter, A. Irmler, P.G. Weidler, H. Gliemann, F. Pauly, V. Mugnaini, M. Zharnikov, Ch. Wöll, ACS Applied Materials & Interfaces, 7, 9824, (2015)
The miniaturization trend in the semiconductor industry has led to the understanding that interfacial properties are crucial for device behaviour. Spintronics has not been alien to this trend, and phenomena such as preferential spin tunnelling, the spin-to- charge conversion due to the Rashba–Edelstein effect and the spin–momentum locking at the surface of topological insulators have arisen mainly from emergent interfacial properties, rather than the bulk of the constituent materials.
In this talk, I will describe inorganic/molecular interfaces by looking closely at both sides of the interface: the molecular side and the inorganic side, as schematically depicted in the figure. For the molecular side, focus is put on the description of how the orbitals of the free molecule develop as a function of the distance from the metal surface, i.e., when the hybridization with the metallic substrate is slowly turned on. This results in a description in terms of the energy level alignment at the interface, of the spin and charge transport across the interface, and of the magnetic coupling between the magnetic moments on the metal and on the organic components. On the other hand, when looking at the interface from the inorganic side, focus is put on the modification of the local spin and electronic properties of the surface atoms (such as the exchange constant and the local magnetic moment) induced by the hybridization of the molecular component.
I will review recent developments in the field of molecular spintronics within this framework, and underline how molecular materials have arisen as an ideal platform for creating interfacial spin effects [1]. As an example for the molecular side description, I will discuss the spin-filtering properties of the Co-Alq3 interface [2]. Within the inorganic side description, I will show that the extreme multi-functionality of organic molecules can be used to control the spin properties of surfaces with a spin-texture induced by strong spin-orbit coupling. I will present our results on the following two-dimensional electronic systems: the surface states of the topological insulator Bi2Se3 [3], and the Rashba-split surface states of a Pb-Ag surface alloy [4].
To conclude, I will discuss the key role that molecular interfaces may play in the development of a new generation of spin-based technologies, thanks to their unique capability of being actively tuned to reach as-yet unexplored functionalities [1].
References
[1] M. Cinchetti, A. Dediu, L. Hueso. Nature Materials 16, 507-515 (2017);
[2] A. Droghetti, P. Thielen, I. Rungger, N. Haag, N. Größmann, J. Stöckl, B. Stadtmüller, M. Aeschlimann, S. Sanvito, and M. Cinchetti, Nature Communications 7, 12668 (2016);
[3] S. Jakobs, A. Narayan, B. Stadtmüller, A. Droghetti, I. Rungger, Y. S. Hor, S. Klyatskaya, D. Jungkenn, J. Stöckl, M. Laux, O. L. A. Monti, M. Aeschlimann, R. J. Cava, M. Ruben, S. Mathias, S. Sanvito and M. Cinchetti. Nano Letters 15, 6022 (2015);
[4] B. Stadmüller, J. Seidel, N. Haag, L. Grad, C. Tusche, G. van Straaten, M. Franke, J. Kirschner, C. Kumpf, M. Cinchetti and M. Aeschlimann. Physical Review Letters 117, 096805 (2016).
Thin-disk laser (TDL) oscillators generate directly ultrashort pulses at megahertz repetition rates and high average powers. Achievable peak powers in the mega-watt level make it a promising driver for nonlinear experiments. Recent progress of mode locking via the Kerr effect enabled the generation of pulses with durations as short as Yb-doped bulk oscillators. We present the status about our Kerr lens mode locked TDL of the gain materials Yb:Lu$_{2}$O$_{3}$ and Yb:CALGO, emitting the shortest pulses ever demonstrated by their gain materials and up to 40 % shorter than previous TDL, and discuss the potential for further power scaling.
Quantum cascade lasers (QCLs) have matured as key-enabling devices for various applications in the mid-IR spectral region between 3-12 µm. They range from food-safety and medical diagnosis to spectroscopy of trace-gas molecules. We will review our recent work on developing highly-integrated and miniaturized laser-detector systems for spectroscopy including bi-functional active region designs (i.e. identical-wavelength emission and detection). Special emphasis is put on surface-emitting ring-cavity waveguides based on 2nd-order DFB-gratings including features like farfield-manipulation, polarization-control and multi-ring designs as well as the implementation of plasmonic waveguides for ridge-emitters to realize lab-on-a-chip configurations. The ring-QCLS are used in gas-sensing and the ridge-emitters in liquid-spectroscopy experiments, respectively.
We present a provisional design of a compact synchrotron light source producing EUV radiation for application in the semiconductor industry. EUV light sources are of great potential interest for this industry. The availability of highly reflective mirrors at 13.5 nm wavelength makes EUV lithography a strong candidate for next generation semiconductor manufacture. Our design is based on a storage ring lattice employing design principles similar to those used in the new family of diffraction limited synchrotron radiation sources. The 430 MeV storage ring, of circumference 25.8 m, would have an emittance of ~ 6 nm-rad. The required EUV wavelength is obtained using a single short-period (16 mm) undulator.
Helium clusters produced via supersonic jet expansions in ultra-high vacuum have wide range of size distributions. Nevertheless, their narrow and size independent velocity distribution has been employed as a key factor for size selection. In this study, same is achieved through passing the ionized helium droplets through deflection in a 90° cylindrical electrostatic sector. This allows precise control of size selection in helium nanoclusters, which further facilitates capping the size of dopant nanostructures. This technique allows creation of clusters and nano-particles in an ultra clean and inert environment without the aid of any ligands, solvent or additives; thereby giving it a significant technological advantage over competing methods.
Nanoindentation has become a popular method for determining Young’s Modulus (E) of materials. Though for most materials this method has been successfully applied, significant errors of the results can occur if materials respond unfavorably to standard indentation parameters. This paper presents an investigation of the effects of nanoindentation on Yttria-stabilized Zirconia compared to bulk properties obtained from Resonant Ultrasound Spectroscopy. We not only observed different results for each method, but also a significant change of E with indentation depth. Analysis of the indents with Raman spectroscopy revealed an indentation-induced phase transformation in the material. In conclusion, researchers should therefore be careful when choosing their method of determining E.
The presentation provides an overview of the current developments in superconducting magnets for applications in proton and ion therapy gantries. It summarizes the benefits and challenges regarding the utilization of these magnets from the economical, infrastructural and technical points of view. The options for material choice, magnet geometry, cooling system and beam optics design are reviewed. The challenges of fast magnet ramping and large stray fields are discussed. Also, the examples of currently used superconducting particle therapy systems and proposed designs are provided. The technical benefits and risks of these designs are discussed and the potential new treatment and patient diagnostic options are mentioned.
Icing of heat exchangers is a commonly observed phenomenon. It subsequently leads to blocking of the air flow and reduced heat transfer capabilities. We focus on the experimental characterization of heat exchanger icing using transient weight measurements and image capturing and extraction techniques. We then compare these observations with numerical simulations on a small symmetric section of the heat exchanger in detail and for a full numerical setup of the whole heat exchanger used to calculate pressure drop and heat transfer capabilities. During the subsequently icing of the heat exchanger, also changes in the acoustic emissions can be observed, which are captured using an acoustic dome and an acoustic camera.
Over the past years there have been several approaches to find positioning techniques in indoors environments. Methods based on Bluetooth beacons, Wi-Fi and other infrastructures are common but come with high installation and recurrent maintenance costs.
This work attempts to exploit geomagnetic field distortions caused by a building’s ferromagnetic structural elements for landmark detection and, by combination with Pedestrian Dead Reckoning, build an algorithm which reconstructs a travelled path based only on data recorded by the smartphone’s accelerometer, gyroscope and magnetometer sensors.
The results are compared to current efforts concerning geomagnetism based indoors localization systems. Finally, accuracy bottlenecks and possible improvements are discussed.
With increasing resolution of regional climate models (RCMs), glaciers may now cover substantial portions of climate model grid cells. This study thus aims at explicitly resolving glaciers in RCMs.
A methodology based on the mosaic approach has been developed to include the heterogeneity of glaciers surface characteristics in glaciers mass balance simulations and surface energy fluxes computation.
Validation of the mosaic approach was performed at 5 study sites in the Rocky Mountains. The atmospheric data to drive the model were provided by the fifth generation of the Canadian RCM.
After a calibration procedure, simulated and measured mass balances correlated well. Biases in precipitation were the main source of error.
We create polarization entangled, spectrally broadband photon pairs from parametric down-conversion in semiconductor Bragg-reflection waveguides. We show, how to adjust the coherence of the polarization entangled states by controlling the relative temporal delay between a pair of photons with a birefringent retarder.
Otherwise, the slight temporal walk-off of the photon pair, which is caused by the highly dispersive waveguide, results in an uncompensated phase. Our experimental and theoretical results show, how the state characteristics can be tuned directly at the source, offering a simple way to optimize the degree of entanglement.
Different variants of Bell inequalities, such as CHSH and CH, are known to
be equivalent when evaluated on nonsignaling outcome probability distributions. However,in experiments, these probability distributions are estimated using a finite number of samples. Therefore the nonsignaling conditions are only approximately satisfied: the robustness of the violation depends on the chosen inequality variant. We explain that phenomenon and propose a method to optimize the statistical robustness of Bell inequalities. In the process, we describe the finite group composed of relabeling of parties, measurement settings and outcomes, and identify correspondences between the irreducible representations of this group and properties of probability distributions such as normalization, signaling or having uniform marginals.
Quantum memories matched to single photon sources will form an important cornerstone of future quantum-network technology. We demonstrate such a memory in warm Rb vapor with on-demand storage and retrieval, based on electromagnetically induced transparency. We test the memory with laser pulses, attenuated to the single photon level. Their bandwidth is chosen to be 660(10) MHz to simulate the photons emitted by semiconductor quantum dots. In this regime, vapor cell memories offer an excellent compromise between storage efficiency, storage time, noise level, and experimental complexity. For 50 ns storage time, we measure an end-to-end efficiency of 3.4(3) %, extrapolating an intrinsic storage and retrieval efficiency of 17(3) %.
Quantum theory predicts that entanglement can also persist in macroscopic physical systems, albeit difficulties to demonstrate it experimentally remain. Recently, significant progress has been achieved and genuine entanglement between up to 2900 atoms was reported. Here we demonstrate 16 million genuinely entangled atoms in a solid-state quantum memory prepared by the heralded absorption of a single photon. We develop an entanglement witness for quantifying the number of genuinely entangled particles based on the collective effect of directed emission combined with the nonclassical nature of the emitted light. The method is applicable to a wide range of physical systems and is effective even in situations with significant losses.
A basic task necessary for quantum information processing is the ability to faithfully transfer quantum states between distant quantum systems. A very promising platform for the implementation of quantum computers with outstanding controllability consists of superconducting quantum circuits, interacting via photon exchange in the microwave regime, which however are extremely sensitive to thermal perturbations.
Here I present a protocol where a quantum state of photons stored in a microwave cavity is faithfully transferred to a second distant cavity via a waveguide, while being completely immune to thermal noise present inside the waveguide. Quantum error correction protocols are applied to further enhance the robustness against other types of errors and imperfections.
Super-resolution-microscopy is a fast evolving field, revolutionizing traditional optical microscopy. These techniques enhance the precision of optical microscopy beyond the standard resolution limit and reach resolutions of a few nanometers. Here we show that, depending on the polarization of the light emitted by the observed particle, systematic wavelength-scale errors can occur when determining the particle’s position using centroid-fitting techniques. The observed shifts are independent of the numerical-aperture or magnification of the imaging optics. We demonstrate this by imaging a single gold nano-particle with an optical microscope. We observe a shift of the particle's apparent position up to 0.4 wavelengths when varying the polarization of the light emitted by the nano-particle.
The projective simulation (PS) model is a physical approach to artificial intelligence. In the PS model, learning is realized by internal modification of the episodic memory network, both in terms of its structure and the weights of its edges. Through interactions with a task environment, the PS memory network adjusts itself dynamically, so as to increase the probability of performing better in subsequent time steps. Here we consider several examples of environments, in which the PS agent does self-adjustments due to glow, generalization and meta-learning mechanisms. The emphasis is made on examples of the PS agent applied to quantum optics experiments.
Recently, topological classification of quantum phases has been extended from non-interacting insulators to strongly correlated insulators, and further to semimetals. In this talk, I will introduce our recent results on direct visualizations of new topological quantum states with angle-resolved photoemission spectroscopy at SLS, including:
• Direct observations of the metallic surface state and its helical spin texture in SmB6 as evidences of the topological Kondo insulator.
• Direct observations of bulk Weyl cones, surface Fermi arcs and their correspondence in transition-metal monophosphides as experimental evidences of the Weyl semimetal.
The transition metal dichalcogenide 1$T$-TiSe$_2$ is a quasi-two-dimensional layered material that undergoes a commensurate 2 $\times$ 2 $\times$ 2 charge density wave (CDW) transition with a weak periodic lattice distortion (PLD) below $T_{\text{CDW}}$ $\approx$ 200 K. Scanning tunneling microscopy (STM) combined with intentionally introduced interstitial Ti atoms allow, for the first time, to bypass the resolution limitation of STM and to intimately probe the surface PLD. This study opens a new avenue for STM to access the directions of the three-dimensional atomic displacements of the PLD and directly questions recent claims of a chiral CDW phase.
The transition-metal dichalcogenide TiSe$_2$ is a layered material with a charge density wave (CDW) transition temperature around 200 K. Its origin is still a matter of debate. Using angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy and spectroscopy (STM/STS), the influence of sulfur concentration in TiSe$_{2-x}$S$_x$ is studied. While TiS$_2$ does not show a CDW phase, the CDW in TiSe$_{2-x}$S$_x$ is not strongly perturbed. With ARPES, we study the evolution of band dispersion and CDW gap size as a function of temperature and sulfur concentration. STM and STS monitor the long-range coherence of the CDW as a function of sulfur substitutions. These observations allow enhancing our understanding of CDW formation.
We measured and analyzed the optical response of 1T-TiSe2 at temperatures above the CDW transition. Separate responses of electron and hole subsystems are identified and followed in temperature. We show that neither semiconductor nor semimetal pictures apply in their generic forms, as the carrier scattering is very strong, with the related energy scale $\hbar/\tau$ being of the order of the absolute values of the gap (or indirect band overlap) previously reported. Our analysis indicates that the inter-valley scattering is dominant in the wide temperature range above the transition and directly responsible for the compensation of electron and hole contributions in the Hall coefficient.
It is widely believed that the integer quantum Hall effect (IQHE) is dominated by single-particle interaction. In a recent paper we show that quite oppositely the IQHE regime behaves similarly to a non-interacting single particle system — not because of the absence, but rather due to the dominance of many-body effects [1]. We utilize a fully self-consistent Hartree-Fock implementation and a model for electron transport close to equilibrium. Our results indicate a strong tendency to avoid the simultaneous existence of partially filled spin-up and spin-down LLs, similar to a Hund's rule for the occupation of the spin split LLs.
[1] J.Oswald, R.A. Römer, EPL 117, 57009 (2017); open access: http://iopscience.iop.org/article/10.1209/0295-5075/117/57009
Recently, the quantum anomalous Hall effect has been observed in Cr and V doped (Sb,Bi)$_2$Te$_3$ [1]. Its eventual technological applications require a homogeneous magnetization without any contribution from dopant bands to the conduction of the system. We combine low energy muon spin rotation and soft-X-ray angle-resolved photoelectron spectroscopy (SX-ARPES) to study the magnetic and electronic properties of these materials. We observe a gradual magnetic transition with full magnetic volume fraction only at doping levels higher than 8% substitution of (Bi,Sb). In addition, resonant SX-ARPES at the V $L_3$-edge reveals the presence of a non-dispersing impurity band at the Fermi level.
[1] C.-Z. Chang, et al., Nature Materials 14, 473 (2015)
Due to the absence of a seizable magnetization in antiferromagnetic spintronics their direct control is difficult and alternative means as, e.g., coupling to a ferromagnet via exchange bias [1], are needed. Antiferromagnetic Co:ZnO was presented as a model system in which uncompensated spins lead to a vertical exchange bias like shift [2] connected to the Co-doping level [3]. We studied temperature and cooling field effects on this vertical shift at different doping levels.
[1] Nogues, J. and Schuller, I.K., J. Magn. Magn. Mater. 192, 203 (1999).
[2] Henne, B. et al., Phys. Rev. B 93, 144406 (2016).
[3] Ney, V. et al., Phys. Rev. B 94, 224405 (2016).
The method of Roman-Perez and Soler [Phys. Rev. B 103, 096102 (2009)], which allows for a fast implementation of the nonlocal van der Waals (vdW) functionals, has contributed in making the vdW functionals popular. However, the Roman-Perez-Soler method relies on a plane-wave expansion of the electron density, therefore it can not be applied to all-electron densities for which an unaffordable number of plane waves would be required for an accurate expansion. We present the results for the lattice constant and binding energy of solids that were obtained by applying a smoothing procedure to the all-electron densities. It is shown that the results agree very well with those from the literature.
Like parent compounds of other unconventional and/or high-$T_c$ superconductor families, BaBiO$_3$ is an unexpected insulator that becomes superconducting (> 30 K) when doped. But bismuth oxides also offer an interesting contrast to other HTSCs, as they have no magnetic order and very weak electron correlations. I will summarize our efforts to revisit these decades-old materials with modern x-ray spectroscopies, ARPES and RIXS, performed in situ on thin films. The investigations give new insights into the nature of the parent state, as well as how the electronic structure and bosonic coupling evolve with doping. We also demonstrate tuning the atomic structure by thin film engineering, which opens new paths for exploration.
We propose a general scheme to probe the compatibility of arbitrary pairing states with a given normal state Hamiltonian by the introduction of a concept called "superconducting fitness". This quantity gives a direct measure of the suppression of the superconducting critical temperature in the presence of key symmetry-breaking fields, even in complex multi-band systems. In the light of this new concept we analyze the multiband superconductor Sr2RuO4 and propose a new mechanism for the suppression of superconductivity, which we call inter-orbital effect, as a possible explanation for the unusual limiting feature observed in the upper critical field in this system.
Ca$_2$RuO$_4$ is an archetypal example for multi-band Mott physics including spin-orbit and Hund's coupling. For decades, the mechanism underlying its Mott insulating state has remained elusive. This talk will present the complete low-energy ruthenium band structure as observed by ARPES in the paramagnetic insulating state of Ca$_2$RuO$_4$ . These results suggest that Ca$_2$RuO$_4$ is a unique example of an orbital differentiated conventional band and Mott insulator. The talk we make a strong effort to explain how this conclusion is reached independently from both DMFT calculations and a purely phenomenological DFT model.
We measured, by angle-resolved photoemission spectroscopy, the electronic structure of LiCu2O2, a mixed-valence cuprate where planes of Cu(I) ions are sandwiched between layers containing one-dimensional edge-sharing Cu(II) chains. We find that the Cu(I)- and Cu(II)-derived electronic states form separate electronic subsystems. The valence band, of the Cu(I) character, disperses within the charge-transfer gap of the strongly correlated Cu(II) states, displaying a 250% broadening of the bandwidth with respect to the predictions of density functional theory. Our observation is contrasting the widely accepted tenet of many-body theory that correlation effects yield narrower bands and suggests that present-day electronic structure techniques provide an intrinsically inappropriate description in late transition metal oxides.
DFT+U is a simple and powerful tool to model systems containing partially-filled manifolds of localized states. Conceptual and practical methods to determine U ab initio have been introduced long ago, based either on the constrained random-phase approximation or on linear-response theory. However, these approaches are often overlooked due to their cost or complexity. Here, we introduce a computationally efficient approach to determine U, hitherto obtained from the difference between bare and self-consistent inverse electronic susceptibilities evaluated from supercell calculations. By recasting these calculations in the language of density-functional perturbation theory we remove the need of supercells, and allow for a fully automated determination of susceptibilities and Hubbard parameters.
The Future Circular Collider is a design study to explore post LHC possibilities at the high energy and high luminosity frontier for electron-positron and hadron-hadron colliders. With the conceptual design report foreseen for the end of 2018, active research in the area of detector concepts and performance is currently ongoing. In particular the detector for hadron-hadron collisions at a center of mass energy of 100 TeV and up to 1000 instantaneous proton-proton collisions will be operated in harshest environment. We present current ongoing detector design studies and benchmarks for the FCC-hh reference detector, the main motivation for the current layout and technology choices and its potential performance and physics potential.
As a result of 2013 Update of the European Strategy for Particle Physics the Future Circular Collider hadron-hadron (FCC-hh) with 100 TeV CM collisions has emerged as one of the future options in the post-LHC era. The beam-beam interaction, being the strongest non-linearity of the machine, has implications in many aspects. A robust design should take into account the different optics and crossing schemes and evaluate the long range interactions effects as well as the impact of large head-on beam-beam interactions. Different compensations techniques are also explored as possible mitigation to the detrimental effects on beam lifetimes and emittance degradation.
The Paul Scherrer Institut (PSI), in collaboration with CERN and the Lawrence-Berkeley National Laboratory, is contributing to the Future-Circular-Collider (FCC) Design Study by exploring the canted-cosine theta (CCT) technology for its suitability for an FCC 16-T main dipole magnet. This design constitutes a departure from classical design patterns, presenting us with, both, opportunities and challenges. In order to establish the CCT option as a viable contender, PSI has launched an effort to build a 12-T technology demonstrator magnet, exhibiting many of the specific features, that would be required for an FCC magnet. We will discuss PSIs efforts in this direction, as well as other potential applications of superconducting CCT technology.
The beam in high-energy accelerators generally causes electron production, through rest gas ionization or photoelectrons generated by the beam synchrotron radiation. Under certain conditions, the acceleration of such electrons in the field of the beam can lead to the build-up of a dense electron cloud, with several detrimental effects for machine operation. Electron cloud effects posed significant challenges to the operation of the LHC in the past few years. When designing future colliders, such as the FCC, it is thus crucial to identify the necessary conditions to mitigate electron clouds. In this contribution electron cloud build-up and effects are reviewed, and dedicated results for the FCC design study are presented.
Relying on their unique sensitivity to the electronic environment, slow positron serve in applied science for the characterisation of materials. Because the creation of slow positrons is inefficient and stringent radio-safety guidelines, their use is limited to specialized laboratories around the world. We report the realisation of a cyclotron trap assisted positron tungsten moderator for the conversion of positrons from common sources to a mono-energetic eV beam with an efficiency of 1.8(2)%. This is an improvement of almost two orders of magnitude compared to the state of the art moderators. This opens the possibility to envisage a widespread use of positron beams as a common characterization tool.
Hadron colliders, have to store beams for very long periods with very good beam qualities to reach the integrated luminosity goals. The protons stored in the accelerator undergo strong non-linear distortions coming from the accelerator elements (magnets) but more fundamental from the opposite beam with the so called beam-beam interactions. The beam-beam effects are the main source of non-linear distortions with direct impact into the luminosity performances (i.e. emittance degradation, intensity reductions). This study compares the models and measurements performed at the Large Hadron Collider in 2016. Results of this study have motivated the accelerator changes which lead to the luminosity increase of 12% at the ATLAS and CMS experiments.
Pulsed beams have tremendous advantages for precision experiments with cold neutrons. In order to minimize and measure systematic effects, they are used at continuous sources in spite of the related substantial decrease in intensity. At the pulsed neutron source ESS, such experiments will gain up to a factor of 30 in event rate, and novel concepts become feasible. Therefore, the cold neutron beam facility for particle physics ANNI was proposed as part of the ESS instrument suite.
Scientific case, design considerations, concept and expected performances of ANNI will be presented.
The next generation of experiments with muons requires high-quality muon beams. We are developing a device that reduces the phase space of a standard $\mu^{+}$ beam by a factor of $10^{10}$ with $10^{-3}$ efficiency. The phase space compression is achieved by stopping $\mu^{+}$ in cryogenic helium gas with density gradients and applying strong electric and magnetic fields. Several aspects of this device have already been tested. The measurements show that we can achieve efficient muon beam compression, as predicted by the simulations.
This work is supported by SNF grant 200020_172639.
The ultracold neutron (UCN) source at PSI converts fast neutrons from a spallation target into UCN via thermalisation in D2O, subsequent moderation in solid ortho-deuterium (sD2), and finally down-scattering on the crystal lattice of the sD2. The UCN output declines after several hours of continuous operation and a conditioning, consisting of a reduction in the cooling power of the sD2 vessel and heating of its lid for a short period, is applied to recover or surpass the initial rate. To pinpoint the reasons for the decreasing UCN rate and the beneficial impact of conditionings, various parameters of the source which might influence the sD2 behaviour during conditionings are being investigated.
The heat and particles that exit the core region of magnetically confined fusion plasmas typically get deposited on a narrow layer on the vessel wall, resulting in peak heat fluxes that can attain levels above today’s technological limits. A promising solution to address this challenge is to stimulate volumetric momentum and power losses in the plasma boundary region and to establish a regime where the plasma detaches from the wall. We will discuss this process of plasma detachment, its prospects and uncertainties for a reactor scenario, and how the unique geometrical flexibility of the TCV tokamak at EPFL contributes to the understanding and optimisation of this important process.
Understanding the turbulent plasma dynamics in the edge region of magnetically confined fusion plasmas is crucial to assure adequate energy confinement and acceptable levels of plasma-wall interaction. Unfortunately, experimental insights are often hampered by limited diagnostics information. To overcome some of these limitations, a Reciprocating Divertor Langmuir Probe Array (RDPA) is currently being designed for the TCV Tokamak at EPFL. The RDPA will aim at scanning a two-dimensional region of the boundary plasma and it will need to withstand heat fluxes larger than 50MW/m^2 for 0.2s, accelerations up to 400m/s^2, and be resilient to large scale plasma instabilities. Design solutions and other constraints will be presented.
Plasma shaping in tokamaks, influencing energy confinement and plasma stability, is of paramount importance for the design of future fusion reactors for energy production. An improved controller for the plasma vertical instability is developed and integrated on the TCV digital control system. For its design a simplified control oriented tokamak model and loop shaping techniques are applied in a Matlab-Simulink environment. A decoupling scheme for shape and position control is also studied, ensuring the separation of their different characteristic time scales. This novel approach, implemented within the existing architecture, will allow real time control of advanced plasma configurations (e.g.,negative triangularity in H-mode and exact snowflake) on TCV.
The ITER actuator controllers will need numerical test and tuning with a “tokamak simulator” based on 1.5MHD equilibrium/transport model, ideally during pre-shot operation.
Coupling the equilibrium code LIUQE and transport code RAPTOR, the fastest available to our knowledge in their categories, would provide a fast and control oriented simulator for this purpose.
A stable, flexible and fast numerical method to solve for the non-linear coupling is sought. The Jacobian Free Newton Krylov method is investigated in terms of stability against initial conditions and minimum number of evaluations of the non-linear function required.
The Neutral Beam (NB) system for ITER will deliver an ion beam with energy of 1 MeV and current of 40 A. Only NB systems based on negative ions can attain the neutralization efficiency required for the NB system in ITER. Helicon plasmas are a promising candidate for the production of negative ions. The RAID (Resonant Antenna Ion Device) at the Swiss Plasma Center represents a crucial step in understanding helicon plasma physics and negative ions production through volume processes. In this talk the last advances on RAID will be presented including the preliminary measurements of $\mathrm{H^-}$ density by means of Cavity Ring-Down Spectroscopy and microwave interferometry measurements.
DC bias diode and DC magnetron plasma sputtering are used at CERN for niobium thin film deposition on copper radio-frequency accelerating cavities.
A dedicated test bench has been developed to perform detailed plasma characterization in these two sputtering configurations. It consists of a cylindrical magnetron assembly, in which two swept Langmuir probes actuated by independent rotation and translation motion feedthroughs are used. Plasma density and electron temperature profiles can be reconstructed with axial and combined radial/azimuthal resolution.
Plasma characteristics resulting from simulations with a commercial 3D Particle-In-Cell/Monte Carlo code are compared with the experimental data for different pressures.
Perspectives for coating optimization applied to real cavities are discussed.
The AWAKE experiment at CERN aims to create GV/m plasma wakefields over a length of 10 m by using a self-modulated 400 GeV/c proton drive beam. The first AWAKE run is dedicated to study the Self-Modulation Instability. The two-screen measurement aims to measure the radial proton beam distribution 2m and 10m downstream the end of the plasma to show that protons get defocused in the order of 1 mrad. Measuring maximum defocusing angles in this order requires GV/m radial plasma wakefields, which can only be present if the Self-Modulation Instability developed successfully. We present the first two-screen measurement results and we give estimates on the strength of the created plasma-wakefields.
Coherent scattering of light from ultracold atoms involves exchange of energy and momentum so that particles can spontaneously form periodic configurations that simultaneously maximize light scattering and minimize the atomic potential energy. Similar to self-ordering with Bose-Einstein condensates (BECs) inside an optical resonator we study periodic pattern formation in free space by off-resonant counterpropagating, noninterfering lasers. As no spatial light modes are preselected the transition from homogeneous to periodic order amounts to a crystallization of light and ultracold atoms breaking a continuous translational symmetry. In the crystallized state the BEC acquires a phase similar to a supersolid with emergent length scale allowing gapped phononic excitations gapped due to infinte-range interactions.
In this presentation, I will talk about spatial spin and density self-ordering of a transversely-pumped two-component Bose-Einstein condensate coupled into a single mode of a linear cavity. The onset of the Dicke superradiance phase transition is marked by a simultaneous appearance of a crystalline density order and a spin-wavev order. The self-ordering in our system is driven by a cavity-induced zero spatial-average Raman field and can be considered as a generic order-by-disorder process similar to the random-field-induced order in the two-dimensional classical ferromagnetic $XY$ spin model. However, the seed of the random field in our case stems from quantum fluctuations and is a dynamical entity affected by self-ordering.
Spontaneous emission of atoms in free space is modified by other atoms in close vicinity inducing collective super- and sub-radiance. For two atoms with a single decay channel the antisymmetric superposition state of the two single excited states will not decay spontaneously. No such excited two-atom dark state exists, if the excited state has two distinguishable independent decay channels. However, we show that for an excited atomic state with N-1 independent decay channels one can find a highly entangled N-particle dark state, which completely decouples from the vacuum radiation field. Mathematically, we see that this state is the only such state orthogonal to the subspace of the atomic ground states.
Matter-wave interferometry imprints a periodic structure onto a molecular beam. This provides a ruler on the nanometer scale for measuring a variety of electronic properties of biomolecules in the same setup. Here we demonstrate interference-assisted metrology with provitamin A, vitamin E and vitamin K1 for the first time. The shift of the interference fringes in a static electric field adresses the static susceptibility. Since the central diffraction grating in our interferometer is a standing light wave, the intensity dependence of the fringe pattern allows determining the molecular optical polarizability. Additionally, we calculate static and optical polarizabilities as well as total susceptibilities using molecular dynamics simulations combined with density functional theory.
On our atomchip setup a one-dimensional Bose gas of 87Rb is cooled down to the transverse groundstate of the trapping potential. The wave function of the condensate is manipulated by displacing the potential following a trajectory defined by optimal control. Thus superpositions of transverse vibrational states are prepared.
Their dynamics is probed by measuring the transverse momentum distribution, imaged after time of flight. Although well
described by mean-field theory initially, the system evolves towards a steady state, which is not expected from the mean-field description. Several effects and their influence on the relaxation process have been studied such as the emission of correlated atom pairs from the first excited state.
We study a system of interacting fermions with large spin and SP(N) symmetry. From the Fermi liquid theory we find that the effective mass and inverse compressibility are always enhanced in the presence of interactions. Concerning magnetism, the Wilson ratio can be enhanced, indicating that the system can be made closer to a magnetic instability, in contrast to the SU(N) scenario. We conclude discussing what are the experimental routes to SP(N) symmetry within cold atoms and the exciting possibility to realize physics in higher dimensions in these systems.
This work shows that it is possible to detect phase transitions in condensed matter systems using a novel approach based on machine learning. A neural network is trained on purposefully (mis)labeled data, after which the transition point can be identified from the network's performance. This technique is capable of identifying thermodynamic and topological transitions as well as other non-trivial transitions such as in many-body localization.
The Ba$_3$MIr$_2$O$_9$ family offers a tremendous playground to study the influence of spin orbit coupling (SOC) in the stabilization of a spin liquid ground state. We present here the zero field $\mu$SR study of the $J=1/2$ compounds (M=Y,Sc,In) synthesized in the 6H lattice.
For the Y and Sc ones we found an homogeneous ordered ground state, with transitions at 4.5 K and 10 K respectively, as expected. Interestingly, for the In one, we found no sign of frozen magnetism down to 20 mK which could be the sign of a spin liquid ground state. Our study then rises questions about the different interactions in those compounds.
Due to the unique topology, defects in one-dimensional systems have a profound effect on the physics of quantum systems. In this contribution we will present an extensive experimental inquiry into the effect of disorder in Heisenberg antiferromagnetic S = 1/2 chain. By combining muon and neutron experiments, we have found drastic changes and suppression of magnetism in both static and dynamic properties upon introduction of defects. These findings in initially-gapless systems will be contrasted with the enhancement of magnetism by defects in gapped systems.
We apply field theory methods to $\mbox{SU}(3)$ symmetric Heisenberg chains in the fully symmetric representation, with p boxes in the Young tableau, mapping them into a $\mbox{SU}(3)/(\mbox{U}(1)\times\mbox{U}(1))$ non-linear $\sigma$-model with a non-trivial topological term and a topological angle $\theta =2\pi p/3$. Based on this mapping we argue that $\mbox{SU}(3)$ spin chains are gapped for $p=3m$, while gapless for $p=3m\pm 1$ (for integer $m$). This is confirmed by Monte Carlo calculations on the $\sigma$-model. We further discuss the phase diagram and the renormalization flow of the $\sigma$-model, and its implications on spin chains.
Quantum spin liquids (QSL) exhibit large sensitivity to perturbations,such as the Dzyaloshinskii-Moriya (DM) interaction.Using the combination of Electron Spin Resonance (ESR) and Muon Spin Rotation ($\mu$SR),we studied the DM interaction in QSL candidates.In the triangular-lattice QSL,$\kappa$-(BEDT-TTF)$_2$Ag$_2$(CN)$_3$,our ESR measurements found a staggered moment of $\mu_{\text{s}}$=6$\times$10$^{-3}\mu_{\text{B}}$.The magnetic field dependence of the ESR-linewidth proves $\mu_{\text{s}}$ to stem from the DM interaction.In a new quasi-one-dimensional QSL,(EDT-TTF-CONH$_2$)$_2^+$BABCO$^-$,our ESR and $\mu$SR study confirmed absence of magnetic ordering down to 20mK,partially due to the highly disordered BABCO$^-$ molecular rotor layer.The ESR-linewidth and longitudinal-field $\mu$SR measurements reveal one-dimensional diffusive spin excitations.Despite the sizable DM interaction,the staggered moment remains negligible,owing to the strong disorder introduced by the anion layer.
We report results on the unconventional finite-temperature properties of the localized singlet-triplet excitations in the 2D frustrated magnet $SrCu_2(BO_3)_2$. Performing inelastic neutron scattering, singlet-triplet modes were separated in energy with an applied magnetic field, so that their damping could be studied independently. The $Q$-dependence of the damping mechanism was determined by analysis of the anomalous lineshapes measured at 6.3K, using the two-components damping mechanism proposed in a correlated decay model. Each excited triplet appears equivalently distributed in space, while the applied field creates different thermal populations for $S^z=0,±1$ modes. While the Q-dependence of the damping is equivalent for each mode, we show that triplets undergo faster damping close to $(\pi,\pi)$.
In this talk I will present an overview of our work on gate induced superconductivity in transition metal dichalcogenides. After a short introduction about the technique of ionic liquid gating, I will discuss our observation of a gate-induced superconducting state in MoS2 that persists even when the thickness of the material is reduced to an individual monolayer. I will summarize the key observation concerning the evolution of the superconducting properties with thickness, which are not fully understood at the moment. In the second part of the talk I will concentrate on very recent tunneling spectroscopy experiments that have allowed us to directly probe the superconducting gap as a function of carrier density. In agreement with expectations for an Ising superconducting state, we find that the density of states is not affected by applying in-plane magnetic fields as large as 15 T. We also discuss the indication given by tunneling spectroscopy as to the microscopic nature of the superconducting state and show that many of the observations point to a so-called s+/- state characteristic of two-band superconductivity due to repulsive interactions (analogous to what is considered to be the state in Fe-based pnictides superconductors).
Work done in collaborations with D. Costanzo, H. Zhang, A. Reddy, S. Jo, and H. Berger
We present a detailed scanning tunneling microscopy (STM) study of the thickness and temperature dependences of the CDW order parameter in 1T-VSe$_2$. We show that mapping the real-space charge order over a broad and well-characterized thickness range, unique to STM, provides essential insight. We introduce a robust derivation of the local order parameter and transition temperature based on the real space charge modulation amplitude measured by STM. Both quantities exhibit a striking non-monotonic thickness dependence that we explain in terms of a 3D to 2D dimensional crossover in the Fermi surface topology. This finding highlights thickness as a true tuning parameter of the electronic ground state.
We show that large spin-orbit interactions (SOI) in graphene can be achieved with TMD substrates. SOI is firstly revealed by weak anti-localization effect, and its analysis shows the spin relaxation time is ~0.2ps for all devices, thus strongly suggesting that the induced SOI originates from a modification of the graphene band structure. This is further confirmed by the observation of beating in Shubnikov-de Haas oscillations. Quantitative analysis finds induced SOI to be around 10 meV. Both the robustness of the interfacially induced SOI and its large magnitude make graphene-on-TMD a promising system to realize and explore a variety of spin-dependent transport phenomena, such as spin-Hall and valley-Hall topological insulating states.
The intense research in layered materials showed the rich physics and promising prospective of 2D materials and monolayer.
Still one question remains open: what is the nature of the electronic motion between the layers of 2D materials? The reason for the limited number of investigations comes from an evident practical limit: high quality single crystals, have naturally a reduced thickness in the out of plane direction.
We overcome this limit using the Focused ion Beam.
Our results call for a new point of view on 2D electronic materials. Experimental evidences shows that out of plane transport provide new insight into electronic properties of layered materials.
The metastable 1T' polymorph of monolayer Mo and W dichalcogenides has recently been predicted to realize the quantum spin Hall insulator phase. Furthermore, the coexistence of this polymorph with the stable semiconducting 2H phase has been observed. In the 2H phase, point defects have widely been studied, while the effect of defects in the 1T' phase has not been investigated to date. Here, we fill this gap providing a complete picture of point defects in single-layer MoS2. We consider vacancy, antisite and adatom defects and examine their thermodynamic stability and magnetic properties. We conclude that all considered defects have lower formation energies in 1T'-MoS2 compared to the semiconducting 2H phase.
Topological materials are a novel class of solids with outstanding properties protected by the interplay of topology and symmetry. Some of the phenomena that can be hosted in these materials, from dissipationless electron transport to spin filtering, could be very promising for many technological applications.
Nevertheless, the rarity of materials exhibiting a stable, topologically non-trivial phase at room temperature hinders development.
Here, we screen a comprehensive database we recently developed of about 1800 exfoliable 2D materials, computing topological invariants from first principles (DFT-PBE with spin-orbit coupling) to search for novel topological insulators and to estimate the relative abundance of promising candidates in two dimensions.
With a few exceptions, all metallic Transition Metal Dichalcogenides (TMDs), whether in the 2h or 1t polytype, experience instabilities toward a distortion of the underlying lattice (often referred to as a charge density wave). With the advent of 2D materials, it has been shown that these instabilities persist down to the monolayer limit. The resulting effect on the electronic properties can be either small or significant, depending on the magnitude of the displacement of the atoms from their high-symmetry position. We argue that the underlying mechanism is the same in all of them, although in a different regime: from a weak/intermediate strength of the electron-phonon coupling where the fermiology plays a key role and the Peierls instability provides a good starting point for understanding, to a strong coupling regime where the Fermi surface is irrelevant and a local picture of bond formation is more appropriate.
The purpose of LHCb is to search for indirect evidence of new physics in decays of heavy hadrons. The LHCb detector is a single-arm forward spectrometer with precise silicon-strip detectors in the regions with highest particle occupancies. The non-uniform exposure of the LHCb sensors makes it an ideal laboratory to study radiation damage effects in silicon detectors.
Dedicated scans are regularly taken, which allow a precise measurement of the charge collection efficiency (CCE) and the calibration of the operational voltages.
The measured evolution of the effective depletion voltage $V_{depl}$ will be shown, and compared with the Hamburg model prediction. The overall performance of the LHCb silicon tracker will be presented.
The use of scintillating plastic fibres in combination with modern SiPM detector arrays allows to build intrinsically fast and low mass particle detectors with good resolution and high geometrical flexibility. We present the development of a new class of scintillating fibres which are based on a novel type of luminophores admixed to a polystyrene core matrix, aiming at very fast fibres with high light yield. Their performance is already competitive to state-of-the-art products. In particular, the decay time constants are in the order of 1 ns, which is more than a factor two shorter than the fastest known fibres and makes them especially interesting for time critical applications.
For the LHCb detector upgrade in 2019, the large scale scintillating fibre tracker will be readout with customised 128 channel Silicon Photo-Multiplier SiPM arrays from Hamamatsu. The first production batch of 500 detector arrays have been delivered in May 2017 and first results from the characterisation are shown. The technology provides a high photon detection efficiency, low optical cross-talk, dense packaging and insures fully operational conditions after a neutron fluence of 6 10^11 neq/cm2.
The techniques employed to electrically and functionally characterise the devices will be presented.
As a part of the LHCb upgrade planned for installation during the LHC Long Shutdown\,2, the current LHCb Outer and Inner Tracker will be replaced by a single tracking detector based on scintillating fibres and read out by silicon photo-multipliers.This new Scintillating Fibre (SciFi) Tracker consists of 12 detection planes, covering a total area of 360\,m$^2$. The active elements of the detector are 2.5\,m-long scintillating fibre mats. This contribution provides an overview of the SciFi detector concept and presents the production of fibre mats at EPFL and other production sites. Special emphasis is put on the fibre mat quality assurance, including measurements of its geometrical, optical, and particle detection properties.
The use of multiplexed modules in high intensity environments was not explored so far, due to the e?ffect of ambiguities in the reconstruction of the hit point caused by the multiplexing feature. We present the ?first performance results of multiplexed modules tested at the CERN SPS 100 GeV/c electron beam for intensities up to 3.3 10$^5$ e$^-$/sec/cm$^2$. At these rates, a factor 5 multiplexing introduces more than 50 % level of ambiguity. Our results prove that by using the additional information of cluster size and integrated charge of the induced XY signal clusters the ambiguities can be reduced to a level below 2%.
A novel generation of silicon pixel detectors based on the commercial High-Voltage CMOS (HV-CMOS) technology will be presented. HV-CMOS pixel sensors are depleted active pixel sensors that allow for the implementation of complex in-pixel electronics. This feature, together with fast charge collection, high efficiency and radiation hardness, makes them promising candidates for the next generation of pixel tracking detectors in HEP experiments.
In particular, the HV-CMOS sensors have been proposed for the outermost layers of the new silicon pixel detector that the ATLAS Collaboration will build for the High Luminosity LHC program starting in 2026. Results of laboratory and test-beam measurements of irradiated and non-irradiated HV-CMOS prototypes will be presented.
A novel pixel sensor based on High-Voltage CMOS (HV-CMOS) technology is being proposed for the tracker upgrade of ATLAS, for the HL-LHC. Due to the proximity to the proton-proton collisions region, those sensors will receive high doses of radiation.
In this context, the characterisation of prototype sensors using the Transient Current Technique (TCT) is presented, after irradiation at different levels of dose delivered at the Bern cyclotron facility. The efficiency of charge collection in the active region of the sensors is studied, allowing for a detailed understanding of the sensor response, as well as inputs for a more accurate modelling of the behaviour of the sensors after irradiation in simulations.
Monolithic Active Pixels Sensors (MAPS), based on the HV-CMOS technology, are being developed as a pixel detector prototypes for the ATLAS silicon tracker upgrade. The HV-CMOS technology allows the creation of a pixel sensor using high-voltage on the same die where the CMOS readout circuitry is implemented. MAPS do not require hybridisation to a passive sensor and, therefore, they represent a big advantage for the construction of detectors with big surface areas.
Multiple MAPS devices were developed and submitted. Devices with different pixel readout architecture, buffered and unbuffered, were investigated. Details of the devices will be shown and results from laboratory measurements and tests using particle beams will be discussed.
The nonsupersymmetric nonconformal Witten model augmented by chiral quarks in a D4-D8 brane construction due to Sakai and Sugimoto is a top-down string-theory construction of a gravity dual to low-energy large-N QCD with only one dimensionless free parameter. Used as a phenomenological model it reproduces several features of hadron physics even quantitatively to within 10-30%. This talk summarizes our results for the predictions of this particular holographic QCD model for decay patterns of scalar, pseudoscalar, and tensor glueballs.
We report new measurements of the branching fractions of the decays $\Lambda^+_c \rightarrow \Sigma^+ \pi^- \pi^+$, $\Sigma^0 \pi^0 \pi^+$ and $\Sigma^+ \pi^0 \pi^0$ based on 711/fb of integrated luminosity recorded with the Belle detector at the KEKB asymmetric energy $e^+e^-$ collider near the $\Upsilon$(4S) resonance (charge conjugated decays are implicitly included). All results are obtained relative to the normalisation mode $\Lambda_c \rightarrow p^+ K^- pi^+$. This is the first measurement of the $\Lambda^+_c \rightarrow \Sigma^+ \pi^0 \pi^0$ channel. The measurements of the other modes are significantly more precise compared to previous analyses.
We present a fully differential calculation at NLO of the radiative ($\mu\to\nu\bar\nu{e+\gamma}$) and rare ($\mu\to\nu\bar\nu{e+e^+e^-}$) muon decays in the effective Fermi theory keeping the full dependence on $m_e$. These processes are the irreducible background for the experimental searches for lepton flavour violation by MEG and Mu3e, as they become indistinguishable from the corresponding signals when the neutrinos carry little energy.
Aside from being a fundamental background, these processes are interesting in their own right. Using a tension between BaBar's recent measurement of $\mathcal{B}(\tau\to\nu\bar\nu{e+\gamma})$ and NLO predictions as an example, we show that fully differential NLO calculations are necessary for current and future measurements, especially when very stringent cuts are applied.
Photoproduction of multiple-meson final states is an efficient tool for the
study of sequential decays of nucleon resonances, i.e. decays involving
intermediate excited states. So far coherent reactions have almost not been explored due to the small production cross sections and the background from quasi-free processes.
Here we summarize preliminary results for the coherent
photoproduction of $\pi^0$ pairs and $\pi^0$ triples off deuterium nuclei.
Coherent photoproduction of $\pi^0$ pairs has gained a lot of interest because
this is a possible production channel for the much discussed $d^{\star}(2380)$
di-baryon resonance.
The experiments were done at the MAMI accelerator using a liquid deuterium target and the combined Crystal Ball/TAPS electromagnetic calorimeter.
Photoproduction of pion pairs off (quasi-) free nucleons is important to investigate the excitation spectrum of the nucleon for low energy QCD, in particular for decays via intermediate excited states. Quasi-free production of such pairs off heavier nuclei also figures prominently in the study of the in-medium properties of nucleon resonances. In the present work production of $\pi^0\pi^{\pm}$ pairs off liquid deuterium is analysed using data taken at MAMI with the A2 experiment as a starting point for a detailed investigation of this channel for nuclear targets. Data for a $^4$He target have also already been taken.
The measurement of the cosmic-ray muon flux can be used to infer the density structure of overburden material. The Eiger-mu project proposes muon radiography to map the shape of the bedrock beneath Alpine glaciers. The first test has been performed at Jungfrau region. We installed emulsion film detectors in the Jungfrau railway tunnel. The detectors stayed 47 days and recorded tracks of muons which passed through the glacier and the bedrock. The high-resolution and automatic microscopes at the University of Bern enabled muon absorption rate analysis and yielded a three-dimensional boundary shape between the dense granite bedrock and the ice part in the very uppermost part of the Aletsch glacier.
The particle recently found at the LHC is compatible with the Standard Model Higgs boson. However, the current uncertainties allow associations with extended models thus rendering it essential to investigate the properties of this particle further. The Higgs potential, determined by the Higgs self-interactions, is believed to be the origin of EWSB. As a first experimental step to reconstruct the Higgs potential the trilinear
coupling can be measured in Higgs-pair production. The dominant process is gluon fusion mediated by top- and bottom quark loops. The NLO QCD corrections with the full quark mass dependencies within the Standard Model are presented.
Investigating p-Pb collisions allows for comparative analyses between Pb-Pb collisions (Quark Gluon Plasma) and pp collisions. This analysis uses dielectrons for the probe, as their lack of colour charge allows them to exit the system with few final state interactions.
In order to precisely measure the low-mass dielectron spectrum, a high purity sample of electrons is required. Whilst traditional cuts provide high purity samples, the efficiency typically suffers. This analysis aims to implement machine learning to overcome these drawbacks.
These techniques, and a first look at the low-mass dielectron spectrum from ALICE using the latest LHC p-Pb data, will be presented.
The soft X-ray line of SwissFEL, Athos, is designed to extend the present capability of the existing FEL facilities. Several new operating modes will be tested to allow greater control over the bandwidth, pulse length and synchronisation. After a brief overview of the entire facility, the layout of the Athos line will be presented and the new operating modes described in detail: starting from the baseline optical klystron configuration, up to the very large (> 10%) bandwidth mode which requires the implementation of transverse gradient undulators (TGU). The technical solutions, focusing on the innovative design of the new Apple X undulators, will be finally discussed.
Here I give an overview of some applications of femtosecond time-resolved x-ray methods to study the out-of-equilibrium dynamics of materials. Non-equilibrium pathways represent a novel means of manipulating order parameters, but in order to effectively understand and use these pathways we need experimental means to "see" the dynamics associated with these order parameters. X-rays offer some unique opportunities in this regard, largely due to the photon energy and momentum.
Ultrafast demagnetization is a long standing problem of solid state physics, as the transfer of angular momentum on the femtosecond time scale is not understood.
Spin and time resolved photoemission experiments are able to separate the different aspects of spin dynamics: Close to the Fermi energy, we observe an initial loss of the spin polarization. This is caused by the initial spin flips as well as by transport effects. The driving force for the spin transport is the temperature-induced shift of the spin-split chemical potentials. This leads to the extension of spintronics to the femtosecond domain.
Opportunities for spin and time resolved band structure imaging at FELs will be discussed.
Among graphene related materials, graphene nanoribbons (GNRs) – narrow stripes of graphene – have emerged as promising building blocks for nanoelectronic devices. The lateral confinement in GNRs opens a bandgap that sensitively depends on the ribbon width, allowing in principle for the design of GNR-based structures with tunable properties. However, structuring with atomic precision is required to avoid detrimental effects induced by edge irregularities. A recently developed bottom-up fabrication route [1] allows for the required atomically precise synthesis of GNRs with different shapes and edge structures [2] as well as heterojunctions between dissimilar ribbon segments (e.g. doped/undoped [3], different widths [4]). In this presentation, the emergence of junction states at such hetero-interfaces will be discussed from a conceptual as well as experimental point of view.
Based on a topological classification of GNRs, S. Louie and coworkers have very recently predicted that topological junction states develop whenever two joining GNR segments belong to different topological classes [5]. I will discuss a first experimental realization of such situation, at the example of GNR quantum dot (GQD) heterostructures formed by cross-dehydrogenative coupling of armchair GNRs of width N = 7 (7-AGNRs) [4]. The so-formed intraribbon quantum dots reveal deterministically defined, atomically sharp interfaces between wide and narrow AGNR segments and host a pair of low-lying interface states. Scanning tunneling microscopy/spectroscopy measurements complemented by extensive simulations reveal that their energy splitting depends exponentially on the length of the central narrow bandgap segment. This allows tuning of the fundamental gap of the GQDs over one order of magnitude within a few nanometers length range.
Even more intriguing topological properties are predicted for a family of zigzag edge-extended AGNRs, of which we have synthesized and characterized a first member in some detail. I will show that variations of the AGNR backbone width and the zigzag edge segment spacing drive this family of GNR structures into trivial, metallic and topological insulating phases [6].
[1] J. Cai et al., Nature 466, 470 (2010).
[2] L. Talirz, P. Ruffieux, and R. Fasel, Adv. Mater. 28, 6222 (2016).
[3] J. Cai et al., Nature Nanotech. 9, 896 (2014).
[4] S. Wang et al., Nano Lett., in press (2017).
[5] T. Cao, F. Zhao, S. G. Louie, Topological Phases in Graphene Nanoribbons: Junction States, Spin Centers and Quantum Spin Chains; https://arxiv.org/abs/1702.02674.
[6] O. Gröning, S. Wang et al., in preparation.
Experimentalists at Empa recently succeeded in the on-surface synthesis of a variety of open-shell one-dimensional acenes. Their electronic spectra were obtained by means of scanning tunneling spectroscopy for molecules physisorbed on noble metal substrates. Comparison to theoretical predictions requires a proper treatment of the image charge effect in the renormalization of molecular energy levels at the surface compared to the gas phase. We discuss a method for a self-consistent update of molecular gas-phase single-particle wavefunctions due to the image-charge effect. It turns out that this update is crucial even for a qualitative prediction of fundamental gaps of physisorbed acenes on noble metal substrates.
Edge and π-electron topologies critically influence electronic properties of sp2 carbon frameworks. For example, presence of zigzag edge leads to emergence of localised non-bonding spin-polarised states, while armchair edge correspondingly supports a closed-shell electronic structure. Furthermore, special topologies of π-electron network leads to molecular systems with non-Kekulé structure that host unpaired electrons. Such systems provide a fertile ground for exploring intrinsic low-dimensional magnetism in carbon-based nanostructures. We describe on-surface synthesis of a variety of open-shell nanostructures viz. single molecules, one-dimensional acenes and quasi-one-dimensional graphene nanoribbons via hierarchical on-surface synthesis or on-surface photochemistry, and employ high-resolution scanning tunneling microscopy and spectroscopy to unravel their geometric and electronic structure.
Manganese self-assembles into atomic chains on the Si(001) reconstructed surface. Recently, our combined scanning tunneling microscopy, atomic force microscopy (AFM) and density functional theory (DFT) study revealed a simple necklace-like structure of the Mn chains. The DFT calculated adsorption energies support a single Mn atom adsorption H’ site, however no gain in energy promoting the formation of chains was found. We use atom manipulation techniques to deconstruct the chains and confirm the H’ site model. Moreover, we show that the manipulated atoms dissipate energies, in the damping channel of AFM, that can be compared to the diffusion energies from DFT calculations.
Oxygen vacancies at the LAO/STO interface leave two vacant electrons, one of which stays localized at the Ti3+ ion and another joins the mobile 2DES. The localized electrons in double and higher-order configurations of the VOs may account for the interface ferromagnetism [1]. The mobile ones, coupled to phonon modes by strong e-ph interaction, form large multiphonon polarons fundamentally reducing the 2DES mobility [2]. We use resonant soft-X-ray ARPES and combined density functional (DFT) + dynamical mean field theory (DMFT) to establish orbital character of the mobile and localized electron states at the LAO/STO interface created by the VOs.
[1] F. Lechermann et al., Physical Review B, 90(8), 85125 (2014).
[2] C. Cancellieri et al., Nature Communications 7, 10386 (2016).
Two-dimensional electron gases (2DEGs) in SrTiO$_3$ arise in many configurations, of which the LaAlO$_3$/SrTiO$_3$ interface is a prominent example with remarkable properties such as gate-tunable superconductivity. I will present angle resolved photoemission spectroscopy measurements of the 2DEG induced at the (001) surface of SrTiO$_3$, providing insight into the subband structure that underpins all SrTiO$_3$ 2DEGs. I will further show that the strength and nature of electron phonon coupling in the SrTiO$_3$ surface 2DEG evolves as the carrier density is tuned. At low densities, comparable to those found for the LaAlO$_3$/SrTiO$_3$ system, we observe an itinerant liquid of Fröhlich polarons, which places constraints on theoretical descriptions of superconductivity in LaAlO$_3$/SrTiO$_3$.
The ASACUSA collaboration at the Antiproton Decelerator of CERN aims at a precise measurement of the ground-state hyperfine splitting of antihydrogen, which promises to be one of the most sensitive tests of CPT symmetry. In a Rabi type setup, a dedicated antiproton-positron mixing trap produces antihydrogen atoms, which pass a tunable spin-flip microwave cavity and a sextupole magnet for spin-flip detection, before they are counted in a tracking detector [1].
In my presentation, I will give an overview of the current status of the experiment, as well as the achievements made during the most recent antiproton run at CERN.
[1] E. Widmann et al., Hyperfine Interactions 215, 1 (2013).
The ASACUSA Collaboration at CERNs Antiproton Decelerator plans to measure the ground state hyperfine splitting of antihydrogen to test the CPT symmetry. Part of the spectrometer line is an antihydrogen detector whose task is to distiguish background events from annihilations of antihydrogen atoms which are produced in small amounts. The antihydrogen detector is composed of a position sensitive central detector and a surrounding hodoscope for tracking which is made up of two layers of plastic scintillators which are read out by SiPMs. Results of last years beamtime will be included, during which direct extractions of antiprotons to the detector have been done in order to study the annihilation signal.
POLAR is a new space-borne gamma-ray polarimeter launched in September 2016 as part of the Chinese-Spacelab TG-2. POLAR does optimized polarisation measurements for the 50-500 keV component of GRBs with unprecedented precision by taking advantage of the non-uniformity of the Compton scattering angles. POLAR uses an array consisting of 1600 plastic scintillators to detect the incoming photons. It provides the location and the scattering angle. It has a relatively large effective area and a field of view of half of the sky. Up until April, POLAR has detected about 10 GRBs/month. Preliminary flight results and results from on-ground calibration measurements will be presented along with future prospects.
The main goal of the GERmanium Detector Array (GERDA) is the search for neutrinoless double beta decay (0nbb).
Its existence would imply the violation of lepton number conservation and reveal the neutrino's nature.
In GERDA, detectors made from enriched germanium-76 with a total mass of 35.6 kg are operated in liquid argon (LAr).
Germanium-76 is one of the few candidate isotopes for 0nbb,
and the detectors reach an outstanding energy resolution and purity.
Instrumenting the cryostat with photomultiplier tubes, the scintillation properties of LAr
can be exploited for active background suppression, to reach an unprecedented low background.
We present the latest results on the performance and half-life measurements.
Mu3e is a novel experiment designed to probe for lepton flavor violation in the muon decay into three electrons. Its goal is to improve the current experimental limit by four orders of magnitude and reach a sensitivity of 1 in $10^{16}$ muon decays. The foreseen stopping rate of $10^8$ muons/s generate combinatorial background which could only be rejected by precise time information. A detector consisting of staggered $250~\mu m$ scintillating fibers readout by silicon photomultiplier arrays will discriminate piled up particles with a time resolution of less than a nanosecond. An overview of the design, followed by recent performance results and status of the detector will be presented.
The upcoming measurement at the ETH Zurich Slow Positron Beam aiming at 0.5 ppb precision will be presented. The precursor measurement with a continuous positron beam has been upgraded to include a pulsed beam and a time-of-flight detection scheme to correct for the major systematic error of the experiment, the second order Doppler shift. Additionally the experiment newly uses a field free region avoiding Zeeman and Stark effects.
This work is supported by the ETH Zurich under grant ETH-35 14-1 and the Swiss National Science Foundation under the grant number 200020 159754 and 200020 166286.
We present the latest status report of PERC facility. The PERC (Proton Electron Radiation Channel) aims to meausure the free neutron beta decay with high precission.
Current and planned neutrino oscillation experiments operate in the 0.1-10 GeV energy regime and use a variety of nuclear targets. At these energies, the neutrino cross section is not well understood: a variety of interaction processes are possible and nuclear effects play a significant role. This talk will explore the relationship between neutrino cross sections and neutrino oscillation measurements, and give a brief overview of both fields.
The T2K experiment is a long-baseline neutrino oscillation experiment currently taking data in Japan. By observing electron neutrino appearance and muon neutrino disappearance in an initially almost pure muon neutrino beam, the experiment aims at precisely measuring the parameters ruling the oscillation mechanism. In order to perform these measurements one must determine with high accuracy the expected neutrinos flux at the far detector from the very small rate of interactions observed at the near detector. A precise understanding of the neutrino interaction cross sections is therefore crucial for measuring oscillation phenomena. This talk will give an overview of the T2K experiment and the status of neutrino cross section measurements.
The detection of high energy astrophysical neutrinos by the IceCube Collaboration has paved the way to the field of neutrino astronomy. However, the origin of such neutrinos is still poorly understood and no source has been identified so far. Cosmic rays sources are home to hadronic interactions in which the accelerated particles might produce neutrinos and gamma-rays through the neutral pion decay.
In this contribution, we present the current status of neutrino point sources searches and focus on multi-messenger approaches using time and space coincidence searches with gamma rays, as well as with the directions of ultra-high-energy cosmic rays.
Despite the overwhelming evidence for dark matter from astronomical and cosmological indications at various scales, a clear evidence of a particle which can explain these observations remains absent. XENON1T is a liquid xenon detector capable of exploring a large fraction of the available parameter space for weakly interacting massive particles (WIMPs). The experiment aims to detect WIMP-nucleon interactions using a dual phase time-projection-chamber (TPC) with a total target mass of about 2 tons. The sensitivity to spin-independent WIMP-nucleon cross sections is expected to reach 10^{-47} cm^{2} at a WIMP mass of 50 GeV after two ton-years of exposure. In this talk, current status of the experiment will be presented.
Axion-like particles are good candidates for cold dark matter. They would form a galactic-scale classical field, which on local scales undergoes coherent oscillations. Through their coupling to gluons these particles would induce oscillating electric dipole moments (EDMs) in nucleons and atoms. We analyse data of two neutron EDM experiments: ILL, Grenoble, France (1998-2002) and PSI, Villigen, Switzerland (2015-16), explicitly looking for an oscillating neutron EDM signal. Our analysis is the first direct laboratory search for the ALP-gluon coupling, with improved sensitivity over indirect bounds from cosmological observations.
The DArk Matter Particle Explorer (DAMPE) is a satellite-borne particle detector used to study High Energy Cosmic Rays and Gamma Rays. After its successful launch into a sun-synchronous orbit in December 2015, it has been operating in nominal science operation mode for more than one year, covering large portions of the sky and revealing several bright gamma-ray sources. In this contribution, we discuss the instrument with an emphasis on its capability to measure photons, followed by a discussion on the photon detection analysis. Finally, we present the first analysis results of several bright Gamma-ray sources detected by DAMPE, such as the Geminga pulsar.
The ArDM experiment is designed for direct detection of WIMPs. In 2015, the experiment was commissioned in the single-phase mode at the target size of nearly 1 tonne. The results confirmed the performance and low background behavior of the installation and gave a promising perspective for the planned double-phase runs. Crucial information was derived from the data: the existence of optical-active impurities in the liquid argon, causing the scintillation light attenuation. We discuss results from the data analysis: detector performances, backgrounds, pulse shape studies, and hardware upgrades. Further-on we present activities for DS20k development: exploiting the ArDM infrastructures for tests of light detection modules and qualification of depleted argon batches.
We report a new route to manipulate the electronic properties of a material via vibrational excitation. Using the LCLS free electron laser we investigate the dynamics of the charge order in a manganite film following resonant excitation of a phonon mode to large amplitude. Combining our experimental results with ab initio calculation, we find that the direct nonlinear coupling between the excited mode and the electronic degrees of freedom is sufficiently strong to drive the insulator-metal transition in this material. The generalization of our approach leads to new ways of manipulating materials e.g. shaping their properties on ultrashort timescales.
The planned SwissFEL ATHOS beamline features all necessary parameters for femtosecond time-resolved experiments in magnetism using x-ray absorption spectroscopy and circular dichroism: intense fs soft x-ray pulses with linear and circular polarization.
An exemplary measurement investigates spin currents between two magnetic films separated by a spacer layer: the upper, fs laser pulse excited film launches a spin current which is detected in the lower layer. Such a structure did surprisingly show fs magnetization enhancement in the lower film. X-ray spectroscopy can be used in a unique way to quantitatively probe the spin and orbital moments separately for each layer with femtosecond resolution.
Sn2P2Se6 is a ferroelectric semiconductor with interesting structural properties. In the temperature range between 193 and 221 K, just above the Curie-Temperature, an incommensurate phase emerges. This permanent structural modulation is believed to be the result of two coupled frozen phonon modes.
In our experiment, we photoexcite the material and probe this structural modulation using ultrafast time-resolved x-ray diffraction and observe the dynamics of the two coupled modes across the phase transition. We found that the electronic excitation only couples indirectly via other phonon modes to these two coupled modes.
We used ultrashort x-ray pulses to monitor the structural dynamics associated with the charge density wave (CDW)-state in K0.3MoO3 after photoexcitation. In a first experiment the response to different excitation fluences was investigated. Starting in a regime of coherent oscillations, increasing the excitation fluence leads to a complete melting of the ordered state. Remarkably, a further increase in fluence results in a short recovery of the CDW on a sub-picosecond time scale. In follow-up measurements, we could create a second recovery by applying another photoexcitation to the first one. An understanding of the microscopic mechanisms of this recovery may enhance our theoretical understanding of ultrafast CDW transitions in general.
Ultrafast optical control of correlation-induced order parameters in complex materials is a key challenge en route to new functional materials. Here we employ above-bandgap femtosecond pulses with various wavelenghts to excite EuTiO$_3$ out of its low-temperature antiferrodistortive equilibrium phase. Monitoring the subsequent transient intensity of distortion-induced superlattice reflections via 80-fs hard x-ray pulses at LCLS, we observe a transient increase of their intensities in a sub-ps time window. This represents an optically induced ultrafast increase of the structural order parameter, which stands in strong contrast to the reduction of the distortion with thermal heating in equilibrium. Preliminary DFT calculations identify 4f-hole-doping as possible driving force.
In this study, we examine charge transfer between graphene and molecular semiconductors, parahexaphenyl and C60. Through in-situ measurements of the current, we directly probe the charge transfer as the interfacial dipole is formed. We demonstrate that adsorbed molecules do not affect electron scattering rates in graphene. However, the molecules introduce p-type doping with only about one thousandth of an electron transferred per molecule. In addition, we show results on charge trapping and light-assisted charge transfer within crystalline needles of polar pentacene derivate dihydrotetraazaheptacene, supported by hexagonal boron nitride and graphene.
Recent applications of indigo as a functional building block for organic electronics have renewed the interest in the chemical and physical properties of this molecule. We report on its electronic structure for the isolated molecule as well as for the bulk molecular crystal phases. Further we investigate the optical properties of the bulk phases. For the molecule we employ an optimally tuned range-separated hybrid functional_(OT-RSH) within density functional theory. For the bulk crystals we take into account the screening in the bulk by using an optimally tuned screened range-separated hybrid approach_(OT-SRSH). Regarding the optical properties of the bulk molecular phases we employ time-dependent density functional theory_(TDDFT) to calculate the absorption-spectra.
We have studied the growth of perfluoro-pentacene films on Ag(110) with photoelectron emission microscopy (PEEM) and differential (optical) reflectance spectroscopy (DRS). The setup allows recording PEEM images and DRS spectra simultaneously, providing the unique opportunity to correlate the morphology and electronic structure (PEEM) with the associated optical response (DRS). We will demonstrate how linearly polarized light can be used in PEEM to differentiate between changes of the work function and effects related to the density of electronic states and their particular symmetry. In parallel, the reflectance of linearly polarized light in the DRS experiments can be used to follow the evolution of the optical anisotropy of the organic film.
Cobalt-pyrphyrin (Co-Pyr) is a promising water reduction catalyst. Cu$_2$O(111) and TiO$_2$(110) with monolayer coverage of Co-Pyr were studied for pressures spanning from UHV up to 1mbar of water vapor. Under UV illumination, surface photovoltage shifts of ΔE$_k$=+120meV are observed on Cu$_2$O(111). X-ray absorption spectroscopy of the Co L3-edge was used to monitor the electronic structure of the molecule’s metal center. Comparison to simulated spectra reveals that on TiO$_2$(110), the Co centers partially transform from a +2 to +1 oxidation state upon exposure to water, while on Cu$_2$O(111) they remain in the +2 oxidation state. Our measurements provide insights into properties of Co-Pyr under conditions near those in solar fuel cells.
Hematite is a promising material for electrochemical water splitting with a suitable bandgap, but it shows poor electrochemical performance.
We focus on the (012) surface. At ambient pressure a bulk terminated (1x1) surface termination exists which is converted into a (2x1) reconstruction at high temperature in UHV. Experimental data confirm the reconstruction.
We calculated the surface-phase-diagram with the WIEN2k code and present a new model of the (2x1) reconstruction, which agrees with experiment and is energetically more stable than the one that has been proposed so far. Furthermore, the surfaces’ interactions with water were investigated in both experiment and theory.
Transitions of individual molecules on surfaces are traditionally described with energy barriers and attempt rates using an Arrhenius law. This yields consistent energy barrier values, but the attempt rates are orders of magnitude below expected oscillation frequencies of particles in potential wells. Using LTSTM to measure an individual dibutylsulfide molecule on Au(111), we find that the transition’s barrier and attempt rate depend in a highly correlated fashion on the tip-molecule position. We establish a single-molecule entropy-enthalpy compensation, and discuss an interpretation in terms of multi-excitation entropy. Motivated by these findings, we study the conservative as well as the dissipative interactions between the molecule and the tip in combined SFM/STM measurements.
Recent experimental observations in our laboratory reveal a striking enantioselectivity of the PdGa:A(111) surface with respect to adsorption of the prochiral molecule 9-ethynylphenanthrene.
The findings highlight the great potential of intrinsically chiral intermetallic compounds for the development of novel, enantioselective catalysts potentially applicable in realistic conditions.
Using density functional theory calculations we demonstrate the central role of van der Waals interactions in determining such a dramatic selectivity. Thanks to the MDBsurf approach based on the calculation of the dielectric function in the substrate material that appropriately weights long-range interactions we explain the striking experimental result at the atomistic level.
We consider entanglement in the three partite system consisting of a qubit, an $m$-level and an $n$-level system. In particular, we use tools introduced in [1] to characterize entanglement transformations under stochastic local operations and classical communication (SLOCC). We find evidence indicating that the following picture is true. In case $m=n$, generic states belong to one of infinitely many SLOCC classes. Surprisingly, in case $m \neq n$, generic states belong to one single SLOCC class only. Furthermore, we show that any generic state is convertible to any other generic state of lower dimension.
[1] E. Chitambar, C.A. Miller, and Y. Shi, J. Math. Phys. 51, 072205 (2010)
Iancu and Mukhopadhyay have proposed a semi-holographic model for heavy-ion collisions, where the saturated hard gluons produced at initial stages are coupled consistently to a holographic theory representing the radiatively emitted strongly coupled soft gluons. The goal is to study thermalization with the ultraviolet (UV) modes described by pQCD and the infrared (IR) modes by gauge/gravity duality. I will describe further progress made in this direction, particularly in the limit where the UV description reduces to kinetic/hydrodynamic theory and the IR description to a strongly coupled fluid. The UV and IR are coupled by self-consistently determined effective metrics. We find novel qualitative behavior of the combined system.
The search for heavy Higgs bosons is an important step to probe the parameter space of the minimal supersymmetric Standard Model. We define simplified models for heavy Higgs bosons decaying to supersymmetric particles by using the SModelS framework. We evaluate the viable parameter space by taking into account limits from the Higgs and flavor sector as well as limits from LHC searches for supersymmetry. Furthermore, we characterize the parameter space resulting in maximal signal at LHC.
We discuss a technique for measuring nonlinear functions of a quantum many-body density matrix, such as Renyi entropies with direct connection to entanglement, without performing full state tomography. Our approach, which has direct connection to Random Matrix Theory, consists in implementing an ensemble of random unitary evolution operators, applying them on the many-body state and extracting the desired functions from ensemble averaged observables [1]. We show that our approach is readily implementable with current technology and present applications in one dimensional Spin-Chains and bosonic systems and discuss the possibility to measure therein entanglement dynamics, characterizing intriguing phenomena such as many-body localization.
[1] S. van Enk and C.W.J. Beenakker, PRL (2012)
Quantum Metrology allows one to perform measurements which are quadratically more precise than classically possible. However, the hurdle of implementing the necessary quantum probe states and measurements, whose complexity varies drastically for different metrological scenarios, is usually not taken into account. We show that for a wide range of tasks in metrology, the 2D cluster state can serve as a flexible resource that allows one to efficiently prepare any required state for sensing; the required (entangled) measurements can be performed using only single qubit operations on the cluster. Crucially, the overhead in the number of qubits is less than quadratic, thus preserving the quantum scaling advantage.
We focus on the generation of entanglement among distant parties in a secure way, and with high communication rates.
We show that hashing protocols, a particular class of entanglement purification protocols, enable arbitrary privacy in the presence of noise, even in a setting where the information which noise was applied leaks to the eavesdropper.
As an application thereof we propose a quantum repeater based on hashing. The overhead per repeater station is constant, thanks to the finite yield of hashing. This is in stark contrast to all other long-distance quantum communication schemes previously considered, and opens the way for long-distance communication of big quantum data.
The Poster Session is held on Wed and Thu. All posters are to be presented on both days. However, due to technical reasons, the contributions are only listed in the timetable of Wed.
En prenant l’astronomie comme exemple, nous mesurerons la place de la science dans la société. Nous verrons quelle contribution elle a apporté et amène toujours dans la culture, la géopolitique et la technologie. Nous constaterons que la proximité du chercheur avec le savoir lui donne la responsabilité de contribuer à ce que la science soit “vraiment utile à la société”, comme le demandaient déjà les premiers statuts de la Société Helvétique des Sciences Naturelles (SPHN, dont l’académie suisse des sciences naturelles est issue) il y a deux siècles. Nous prendrons la mesure de cette tâche dans le monde moderne, et décrirons les exigences qui en découlent pour les scientifiques de notre temps.
Precision studies of antihydrogen might shed light on one of the most tantalizing mysteries in today’s Physics: the asymmetry of matter-antimatter abundance in the Universe. In this presentation, we review the developments in the experiments ATHENA and ALPHA, housed at CERN’s Antiproton Decelerator, leading to the first production of low-energy anti-atoms [1] and later the first trapping of antihydrogen atoms [2]. These exotic atoms can be held for over 15 minutes in the trap [3], thus allowing for a new era of high precision measurements of antimatter. Among the initial measurements, we have put new limits on a possible electrical charge of the anti-atom [4] that, together with independent measurements, put new limits on a possible charge anomaly of the positron. Microwaves can induce spin-flipping transitions [5] and allow for the measurement of the hyperfine constant. The main goal of a high precision two-photon laser spectroscopy on the 1s-2s transition has just been started with the observation of the laser excitation [6], and it should evolve into 2017 with a first spectrum leading to comparisons of parts in 1012 between these transitions in antihydrogen and its charge conjugate atom. There are prospects for reaching parts in 1015 and beyond [7], and those will require further cooling of the anti-atoms [8] and the possibility to trap hydrogen in the same trapping environment as the antihydrogen [9]. Whether the CPT (charge-parity-time) symmetry will hold true at these levels of precision or whether gravity acts the same way – probed firstly by “red shifts” on the transition frequencies – on antimatter atoms, only nature has that answer. As experimenters with this exotic species at hand it is our duty to properly inquire nature’s responses on all these issues.
[1] M. Amoretti et al. (ATHENA Coll.), "Production and detection of cold antihydrogen atoms", Nature 419, 456 (2002)
[2] G. B. Andresen et al. (ALPHA Collaboration), "Trapped Antihydrogen", Nature 468, 673 (2010)
[3] G. B. Andresen et al. (ALPHA Collaboration), "Confinement of Antihydrogen for 1,000 Seconds", Nature Physics 7, 558 (2011)
[4] M. Ahmadi, et al. (ALPHA Coll.) “An improved limit on the charge of antihydrogen from stochastic acceleration”, Nature 529, 373 (2016)
[5] C. Amole, et al. (ALPHA Coll.), “Resonant quantum transitions in trapped antihydrogen atoms”, Nature 483, 439(2012)
[6] M. Ahmadi et al. [ALPHA Coll.], Observation of the 1S–2S transition in trapped antihydrogen, Nature 541, 506 (2017)
[7] Ch. G. Parthey et al., “Improved Measurement of the Hydrogen 1S-2S Transition Frequency”, Phys. Rev. Lett. 107, 203001 (2011); C. L. Cesar, “Zeeman effect on the 1S-2S transition in trapped hydrogen and antihydrogen”, Phys. Rev. A 64, 023418 (2001); C. L. Cesar et al., “Two-Photon Spectroscopy of Trapped Atomic Hydrogen”, Phys. Rev. Lett. 77, 255 (1996)
[8] see for example: C. L. Cesar, F. Robicheaux and N. Zagury, “Possible mechanism for enhancing the trapping and cooling of antihydrogen", Phys. Rev. A 80, 041404(R) (2009), and P H Donnan, M C Fujiwara and F Robicheaux, “A proposal for laser cooling antihydrogen atoms”, J. Phys. B 46, 025302 (2013)
[9] C. L. Cesar, “A sensitive detection method for high resolution spectroscopy of trapped antihydrogen, hydrogen and other trapped species”, J. Phys. B 49, 074001 (2016)
Laser-cooled trapped ions are among the most promising candidates for quantum computing platforms. Quantum information can be encoded in ions’ electronic states, where it can be processed with high-fidelity gate operations and read out deterministically. An outstanding challenge, not only for ion-trap computers but for all experimental realizations, is how to link together remote quantum computers. Such quantum networks would enable distributed quantum computing as well as secure long-distance communication over quantum channels.
By coupling an ion to the mode of an optical resonator, we can construct an interface between single ions and single photons, allowing us to transfer quantum information from ions onto photons for distribution over optical channels. I will present probabilistic and deterministic realizations of an ion-photon interface, based on ion-photon entanglement and ion-photon state transfer. Finally, I will discuss approaches to link up future networks and the challenges that we face on the road to scalability.
The recent detection of gravitational waves from coalescing binary black holes by LIGO allowed for the first time the direct observation of stellar-mass black holes. These gravitational wave detections, complemented by a 45-year-long history of indirect observations of black holes in X-ray binaries, can give us now a more complete picture of the formation and evolution of binary stellar systems containing black holes. Yet, to date, a number of physical processes involved in the formation and evolution of these systems remain poorly understood. In this talk I will review our current understanding of the evolutionary channels leading to the formation of coalescing binary black holes. Furthermore, I will discuss the main uncertainties involved in these formation scenarios: the phase of dynamically unstable mass-transfer also known as common envelope, the occurrence of natal kicks during the core-collapse phase leading to black-hole formation, and the angular momentum content of the formed black holes. Finally, I will present an outlook of how we can improve, in the near future, our understanding in all these fronts.
For the “classical” isolated binary evolution, we ran an extensive grid of BH(Black hole)-He star binary evolution tracks, keeping track of the angular momentum evolution of the He star. For a He star with a compact object companion in a close orbit, tides can be efficient only when the orbital period is shorter than ~2 days. Based on the direct-collapse model (no angular momentum loss during the core-collapse), we find that the spin of the second-born BH covers the whole range of the BH spins (i.e. from 0 to 1), and that a weak inverse correlation exists between the merger timescale and the spin of the second-born BH.
The η Carinae binary system hosts one of the most massive stars, which features the highest known mass-loss rate. This dense wind encounters the much faster wind expelled by the stellar companion, dissipating mechanical energy in the shock, where particles can be accelerated up to relativistic energies and subsequently produce very high energy γ-rays. We aim at comparing the variability of the γ-ray emission of η Carinae along the binary orbit with the predictions of simulations to establish the nature of the emission and of the seed particles. We have used data from the Fermi Large Area Telescope obtained during the last 7 years and spanning two passages of η Carinae at periastron. We performed the analysis using the new PASS8 pipeline and its improved instrument response function, extracting low and high energy lightcurves as well as spectra in different orbital phase bins. We also introduced particle acceleration in hydrodynamic simulations of the system, assuming a dipolar magnetic field generated by the most massive star, and compared the γ-ray observations with the predictions of diffuse shock acceleration, in a multi cell geometry. The main source of the γ-ray emission originates from a position compatible with η Carinae and located within the homoncu- lus nebula. Two emission components can be distinguished. The low energy component cuts-off below 10 GeV and its flux, modulated by the orbital motion, varies by a factor less than 2. Short term variability occurs at periastron. The flux of the high energy component varies by a factor 3-4 but differently during the two periastrons. The variabilities observed at low energy, including some details of them, and these observed at high energy during the first half of the observations, do match the prediction of the simulation, assuming a surface magnetic field in the range 0.4-1 kG. The high energy component and the thermal X-ray emission were weaker than expected around the second periastron suggesting a modification of the wind density in the inner wind collision zone. Diffuse shock acceleration in the complex geometry of the wind collision zone of η Carinae provides a convincing match to the observations and new diagnostic tools to probe the geometry and energetics of the system. This demonstrates that Fermi acceleration is at work in the wind collisions and that a few % of the shock mechanical energy is converted in particle acceleration. Further observations are required to understand the periastron-to-periastron variability of the high energy component and to associate it firmly to an hadronic origin. We estimate that η Carinae is a pevatron at periastron and is bright enough to be detected by IceCube observing for many years. Orbital modulations of the high-energy component can be distinguished from these of photo absorption by the four large size telescopes of the Cherenkov Telescope Array to be placed in the southern hemisphere.
Supermassive primordial stars forming in atomically-cooled halos at redshifts 15-20 are currently thought to be the progenitors of the earliest quasars in the Universe. In this picture, the star evolves under rapid accretion (0.1-1 Msun/yr) until the general relativistic instability triggers its collapse to a black hole at masses of ~105 Msun. However, the ability of the accretion flow to sustain such high rates depends crucially on the photospheric properties of the accreting star, because its ionising radiation could reduce or even halt accretion.
We present new models of supermassive Population III protostars accreting at high rates, including general relativistic corrections to the internal structure. We estimate the mass at which the collapse occurs, which gives the upper mass limit of stars that ever formed in the Universe.
We confirm that for high enough rates the stars evolve as red, cool supergiants with surface temperatures below 104 K towards masses above 105 Msun. Compared to previous studies, our results extend the range of masses and accretion rates at which the ionising feedback remains weak, reinforcing the case for direct collapse as the origin of the first quasars.
Under specific conditions, exoplanets and their atmospheres gradually unveiling themselves to our knowledge. Among the best characterized exoplanets, hot Jupiters still show a number of peculiarities that remained unexplained. Among them are the radius anomaly, the presence of clouds that darken atmospheres and the atmospheric evaporation due to different mechanisms. The transmission spectroscopy technique studies the light filtered through the atmosphere of an exoplanet, as it passes in front of its star. These observations have experienced a rapid development in the last few years, allowing us to precisely probe the low part of atmospheres. Despite this progress, we still are unable to understand the link between the low and the upper part of atmospheres, with the latter undergoing evaporation. This last point calls for new types of complementary observations.
My work explored the possibility to use HARPS, a high-resolution spectrograph in the optical domain, in order to measure exoplanetary transmission spectra. It allowed us to measure, for the first time with a medium-size telescope, some high-resolution transmission spectra of hot Jupiters. The studies of sodium lines (via the Fraunhofer D doublet) into the atmospheres of the two hot Jupiters HD189733b and WASP-49b revealed new informations about their thermospheres, whose are very specific region of intermediate altitudes. Some innovative temperatures and winds measurements in these regions complement the observation made at others wavelengths and resolutions. Henceforth, observations at high-resolution, particularly in the optical domain, are a valuable and important resource in order to understand exoplanets atmospheres.
Accurate long-time data of Total Solar Irradiance (TSI) are fundamental to understand solar forcing of climate change. The TSI space radiometers suffered degradations of their cavity detectors due to strong solar exposure. The detector degradation has been a challenge to get accurate space measurements of TSI. Degradation of one routine channel in a TSI instrument onboard a Chinese FengYun-3 satellite is quantified using day observations in 24 months by comparisons with other space TSI sensors. The novel quantifying method has been used for degradation correction of the TSI instrument on the FengYun-3 satellite. The correction method for detector degradation has been validated by comparisons with other TSI space instruments.
We present our spectroscopic and metrological investigations related to the development of next generation high performance vapor-cell atomic clocks. Such precision instruments are crucial for applications such global satellite navigation systems and network synchronisation. Our studies concern both basic atoms-photons resonant interactions (in the microwave and optical domains) and more technological aspects such as compact wavelength stabilised lasers.
Positronium is an excellent system to test bound state QED theory to high precision, since it is almost exlusively governed by the electromagnetic force and does not exhibit finite size effects which plague measurements of protonic atoms.
Numerous precise experiments have therefore been conducted in the past to measure the hyperfine splitting of Positronium. However, these experiments show almost 4σ disagreement with the most recent bound state QED calculations.
PHySES' approach is to eliminate several possible sources of systematics present in earlier experiments by a novel experimental design to conclusively check this discrepancy. This talk will report on the design, the current status, and future prospects of the experiment.
We are investigating the use of laser-cooled anionic molecules to sympathetically cool antiprotons confined in the same trapping potential, which is of interest for antimatter experiments at CERN. A test setup to produce cold ground state C2- molecules is currently being commissioned.
This setup will be presented, together with a theoretical study on the feasibility of several laser cooling schemes, including one using the AC-Stark shift.
Laser cooling of anions --- which has so far never been achieved --- would also enable the sympathetic cooling of any other negatively charged species, opening new opportunities in a variety of research areas.
We report on measurements and simulations on a superconductor tube in the presence of inhomogeneous magnetic fields in a cryogenic environment. The effect is studied using Hall sensors in a table top experiment. The suppression of external magnetic fields in a controlled manner is important for precision experiments in cryogenic environments in atomic physics and antimatter experiments. Also the effects of field trapping are discussed.
The Pauli Exclusion Principle (PEP) is the foundation for our understanding of physics where systems of fermions are concerned. Therefore, it is important to make precision tests of the PEP. In a pioneering experiment, Ramberg and Snow supplied an electric current to a Cu target, and searched for PEP violating atomic transitions of the “fresh" electrons from the current. The non-existence of the anomalous X-rays from such transitions then set the upper limit for a PEP violation. The VIP2 (VIolation of Pauli Exclusion Principle) experiment improves this method. The experiment and the preliminary results from the first data taking period in the underground laboratory of Gran Sasso will be presented.
Progress in low emittance electron storage ring design necessitates an upgrade of the Swiss Light Source (SLS) in order to stay competitive in the future.
For the period 2021-24 it is planned to replace the storage ring by a new one providing 30-40 times lower emittance and correspondent higher brightness and coherent fraction. A novel type of lattice was developed to provide an emittance of about 125 pm.rad at the SLS energy of 2.4 GeV and within the comparatively small circumference of 290 m. A conceptual design report is in preparation.
Atomic scale X-Ray Photon Correlation Spectroscopy (aXPCS) is a powerful technique to study the dynamics on an atomic scale in hard condensed matter by using coherent high flux X-ray radiation. It is shown that using such beams to probe the dynamics in hard condensed matter also induce dynamics in the material. Measurements of the influence of X-rays on the dynamics in a wide range of different oxide glasses were performed including the whole range of alkali borate glasses with different alkali concentrations, alkali and lead silicates, vanadium phosphate glasses and vitrous boron oxide. Results obtained from different materials are compared and first conclusions about the phenomenon are presented.
It is well known that in some cases powerful synchrotron X-ray sources are not only probing but at the same time also influencing the structure
of the sample.
Recently it was shown that coherent X-rays with a high flux as used in aXPCS (atomic scale X-ray Photon Correlation Spectroscopy) measurements influence the dynamics on some kind of materials like oxide glasses.
On the basis of aXPCS experiments on alkali silicate and alkali borate glasses the beam-induced dynamics will be presented in detail as well as the q-dependence of the correlation times
and corresponding theoretical diffusion models.
In situ small angle X-ray scattering (SAXS) is a suitable technique to analyze global ion fluxes and local ion re-arrangement in nanoporous carbon-based supercapacitor electrodes upon charging and discharging.[1,2] Recently, we have extended our studies to include volumetric changes of the electrodes during operation. Therefore, a novel hierarchical carbon material with ordered mesoporosity and tunable disordered microporosity was synthesized. This system provides the unique possibility to track electrode expansion and compression on the nanometer and the macroscopic scale by combining in situ SAXS and electrochemical dilatometry.[3]
1 C. Prehal, et al. Energy Environ. Sci.,2015,8,1725-1735
2 C. Prehal, et al. Nat. Energy, 2017,2,16215
3 C. Koczwara et al. 2017 submitted
Transient absorption is a widely used technique in ultrafast spectroscopy. In this contribution we show how the correlation of the noise on the employed light source can be used to reduce the measurement time by two orders of magnitude without need to increase the repetition rate of the laser system or the light exposure of the sample. Besides being an important progress in itself, the gain in photometric resolution can be used to resolve small changes in transient anisotropy which are otherwise difficult to access by time-resolved broad-band spectroscopy in the visible domain.
The extreme ultraviolet (EUV) is of particular interest for future lithography replacing 193 nm UV by, e.g., 13.5 nm radiation from Sn plasma. Here, instead of lenses Mo/Si multilayer structures are considered. These structures are one-dimensional photonic crystals (1D-PhCs).
In this work, the EUV reflectivity of more complex PhCs are studied. For example, by replacing every 4th Mo layer by Si a 1D superlattice PhC is constructed. 3D PhC studied have, e.g., the woodpile structure (layers of parallel rods, with the rods in adjacent layers oriented perpendicularly).
The reflectivity is calculated using the multiple scattering method and the FDTD method.
Diffuse scattering from thermally populated phonons contains important details on elastic and thermodynamic properties. I will show that high-precision measurements of thermal diffuse scattering together with a rigorous data analysis allow for the determination of the full elasticity tensor in a single crystal diffraction experiment 1.
The new approach allows the measurement of elastic properties together with the crystal structure in the same experiment and offers the opportunity to study tiny single crystals regardless of shape, symmetry and optical properties.
1 B. Wehinger, A. Mirone, M. Krisch, and A.Bosak, Full Elasticity Tensor from Thermal Diffuse Scattering, Phys. Rev. Lett. 118, 035502 (2017).
Quantum state tomography is an approach to reconstruct a quantum state but involves a lot of computational post-processing. So in 2011 a novel more direct method was established, without the post processing, using so called weak measurements. However, because of this weakness the information gain is very low. Now we managed to combine these two methods and got the benefits from both. Our procedure is based on the method established in 2011, without the need of computational post processing, but at the same time uses strong measurements, which makes it possible to determine the quantum state with higher precision and accuracy, which is demonstrated in a neutron interferometric experiment.
Using loop quantum gravity as an example, I will present how essential aspects of relativistic spacetime disappear in quantum gravity. The absence of spacetime in a fundamental theory of physics seems to undermine the conditions necessary for its empirical confirmation and thereby threatens what could be called its 'empirical coherence'. I will sketch how relativistic spacetime is thought to be recovered in loop quantum gravity, and how this averts the threat of empirical incoherence.
The year 1955 marked the celebrations of the fiftieth anniversary of the formulation of special relativity by Albert Einstein. André Mercier, then head of the Theoretical Physics Department of the University of Bern, the city where the theory was formulated, decided to organize a large international conference to celebrate Einstein’s achievements. He obtained the prestigious support of Wolfgang Pauli who accepted to chair the conference. Held in July 1955, the conference turned out as the first ever international meeting entirely devoted to subjects related to general relativity. It initiated a tradition of international conferences devoted to this field. The 1955 meeting in Bern was also instrumental in the recognition of a distinct community of scholars, the relativists, in the time of the « Renaissance » of Einstein’s theory of gravitation. Indeed, after thirty years of stagnation, the fifties marked the return of general relativity and gravitation to the mainstream of physics. My presentation intends then to present the role played by the 1955 Bern Conference as an institutional innovation in the process of the « Renaissance » of general relativity.
Stefan Meyer - Director of the Radiuminstitut der Akademie der Wissenschaften in Wien – published 1937 a paper on the “age” of the sun (1).
1938 soon after this publication Stefan Meyer had to retire and quit the Membership of the Academy when the national socialists took over.
The outcome of this research was published by F.F. Koczy in 1943 in Nature (2) – thus at a time Stefan Meyer stayed in Bad Ischl escaping from the national socialist regime. This research topic will be discussed.
(1) Meyer, S., Mitteilungen Inst. f. Radiumf., No. 393 (1937), No. 407.
(2) F. F. Koczy, Nature 151 (1943) 24.
Karl Przibram (1878 – 1973) studied at the Universities Vienna and Graz. 1902/03 he worked at the Cavendish Laboratory in Cambridge under J. J. Thomson. He continued his research on electrical discharges as a Private Lecturer at Ludwig Boltzmann’s institute. His memories of the old institute in the Türkenstraße, where the first women studied physics, are fascinating. He created several caricatures of Boltzmann. In the Radium Institute he investigated the colouring of crystals by radioactive radiation. He discovered the radiophotoluminescence and coined the term “colour center”. The Nazi period he survived in Bruessels. His followers applied the method of irradiation to metals. Important is his book “Irradiation Colours and Luminescence”.
The diffusion of gases, dry and moist, had been studied in 1874 by L. Dufour, who observed a pressure difference across a porous wall separating moist air and a vessel containing either water or a desiccant. 70 years later, H. Greinacher (1880-1974) claimed to have built the first Diffusion Hygrometer, proposed a theory and got a patent for it. Two different models were produced by firms of Lausanne, TESA and Rueger. Eventually, they were a commercial failure. We found one exemplar of each maker in the collections of our Physics Museum and have tested them. A comparison of the performances with the then currently available hygrometers will be made.
Since 2014 the Museum of the History of Physics of the University of Padua has been working on the study and valorisation of the collection of historical scientific instruments kept at the high school “Scipione Maffei” in Verona, one of the oldest high schools in Italy. The Cabinet of Physics of “Liceo Maffei”, founded in 1802, not only documents the evolution of physics teaching in an Italian high school in the 19th and 20th centuries, but it also highlights the fact that high schools in 19th-century Northern Italy were also research centers. This paper will mainly focus on this latter aspect and I will examine in particular the scientific contacts between Giuseppe Zamboni, professor of physics at the “Liceo” from 1804 to 1846 and inventor of the dry battery, and Salvatore Dal Negro (1768-1839), professor of experimental physics at Padua University from 1806 to 1839.
Magnetic Force Microscopy (MFM) is a versatile tool to map the stray field emanating from a sample surface with high spatial resolution and sensitivity, and in applied magnetic fields up to several Teslas.
The technical aspects of MFM will be reviewed and examples of high current interest such systems exhibiting interfacial Dzyaloshinskii-Moriya interaction (DMI) will be discussed. The average Dzyaloshinskii-Moriya (DM) interaction D, and the exchange stiffness A can be extracted from MFM data of the domain structure obtained after different demagnetization procedures. Local values of D, Ku, and A can be obtained from fitting model skyrmion magnetization structures to MFM data. We find that the local values of D are substantially larger than the average value, indicating that in our system, the skyrmions are strongly pinned. Apart from the domains and skyrmions MFM can also detect small field variations arising from a local variation of the areal magnetic moment density that can be attributed to a corresponding variation of the Co layer thickness. High-resolution and quantitative MFM is thus a powerful experimental method to assess local magnetic sample properties relevant for the development of future skyrmionic devices.
Skyrmions are topologically protected spin whirls envisaged as promising information carriers. In this talk, we report both writing and erasing skyrmions with moderate electric fields in Cu2OSeO3. Using neutron scattering, we demonstrate that the skyrmion pocket either expands or shrinks significantly depending on the direction of electric fields, allowing us to write or erase the skyrmion phase in bulk. The effect is addressed theoretically by using the framework of fluctuation-induced phase transitions and the first order perturbation theory in electric fields. As the electric field is almost not heating the insulating Cu2OSeO3 samples, our study provides further perspectives for dissipation-free electrical control of skyrmions in insulators.
Magnetic skyrmions are topologically non-trivial nano-scale spin textures having raised great interest not only for their unique physical behaviors, but also for the potential applications in spintronics. In thin crystals of helical magnets, the skyrmion phase coexists with the topologically trivial helical and field-polarized phases over large portions of the phase diagram.
Here we use an ultrafast TEM in Lorentz-Fresnel imaging mode to report the creation of skyrmions by a single optical pulse in a 50 nm-thick crystal of the helical magnet FeGe. We show that it is possible to create stable skyrmions in a wide region of the phase diagram. Possible mechanisms responsible for skyrmion formation will be discussed.
Controlling magnetization using piezoelectric strain offers unprecedented power efficiency for next-generation spintronic devices. However, strain is a uniaxial effect and, unlike directional magnetic field or spin-polarized current, cannot induce a full 180° reorientation of the magnetization vector when acting alone. We have engineered novel “peanut” and “cat-eye” shaped nanomagnets on piezoelectric substrates that undergo repeated deterministic 180° magnetization rotations in response to individual strain pulses by breaking the uniaxial symmetry using shape anisotropy. This behavior can be likened to a magnetic ratchet, advancing magnetization clockwise with each piezostrain trigger. The results were validated in micromagnetics simulations. This work provides a simple and effective design for developing future spintronic applications.
We study ultra-thin films of Fe magneto-electrically coupled with a ferroelectric substrate PMN-PT (001) .We have grown ultra-thin wedge of Fe with thickness varying from 1 ML to 5 ML on PMN-PT (001) under ultra-high vacuum conditions. We employed x-ray magnetic circular di-chroism (XMCD) technique at, the Fe L3, 2-edges. The results for the Fe wedge (1-5 ML) shows that the thinner part (1 ML) is paramagnetic while the thicker part (5 ML) is ferromagnetic. Furthermore, we measured a change in the remanent spin magnetic moment for 5 ML of Fe upon switching the ferroelectric polarization of PMN-PT (001).
Charge-mediated control of magnetism has been found in many systems. Here we present an approach to controlling magnetism through field effects using a silicon nitride membrane as gate dielectric. A Pt/Co/Pt tri-layer structure is grown on a high resistance silicon nitride membrane and an electric field is applied out-of-plane. Magnetic characterization is performed with Magneto-optic Kerr effect (MOKE) and Photoemission electron microscopy (PEEM). We find that the electric field modifies the magnetic anisotropy and induces nucleation of new magnetic domains. We find that the charge modulation at the interface reduces the energy barrier for domain wall nucleation by 10%, explaining such an effect.
Most of the digital information today is encoded in the magnetization of ferromagnetic domains. Writing a bit is usually achieved by rotating domains, which relies on magnetic fields. An alternative approach is to change the magnetic state directly by changing the interaction between spins. Correlated oxides are ideal materials for this because the effect of small external control parameter is amplified by the electronic correlations. Here, we present a radically new method for reversible, light-induced tuning of ferromagnetism at room temperature using a CH3NH3PbI3/La0.7Sr0.3MnO3 heterostructure. We demonstrate that photo-induced charge carriers from the CH3NH3PbI3 photovoltaic perovskite efficiently dope the La0.7Sr0.3MnO3 thin film and melt the ferromagnetism.
The spin Hall effect in a current-carrying wire leads to the accumulation of spins at the outer edges of the wire. We detect this spin imbalance by magneto-optical Kerr microscopy and find that the Kerr rotation for Pt and W has opposite sign, as expected from the respective spin Hall angles. The measured spin accumulation scales linearly with the applied current density. In thickness-dependent measurements as well as in ab-initio calculations we find a spin diffusion length in Pt of $9 \pm 2$ nm, significantly larger compared to a Pt film that is in contact with a magnetic layer.
Recently we have combined a scanning transmission x-ray microscopy (STXM) setup with a novel microwave synchronization scheme for studying high frequency magnetization dynamics in the GHz regime [1] enabeling spatially resolved ferromagnetic resonance (FMR) studies on magnetic micro- and nanostructures. Compared to other spatially resolved FMR detection schemes [2] the STXM-FMR setup features element-selectivity as well as high temporal and spatial resolution down to 18 ps and 35 nm [1]. We will briefly present the STXM-FMR detection [1] and first results for coupled magnetic structures (Co stripe coupled to Py dot).
[1] S. Bonetti et al., Rev. Sci. Instrum. 86, 093703 (2015)
[2] R. Meckenstock, Rev. Sci. Instrum. 79, 041101(2008)
The NA64 experiment is a new experiment searching for invisible decays of dark photons using the electron beam of the CERN SPS dumped in an active target.To obtain the aimed sensitivity of NA64 to a single A'-decay for >$10^{10}$ eots, one of the key elements that is the use of an incoming electrons tagging with efficiency better than 95% and suppression of hadrons contamination in the e$^-$ beam down to the level < $10^{-5}$.The results obtained with a prototype version of the e$^-$ tagging system based on the detection of synchrotron radiation by BGO detector are presented.
As part of R&D studies related to dark matter searches, we have designed, built and operating new, small-scale dual-phase xenon TPC at the University of Zurich. Detector performance is comparable to the state-of-the-art xenon-based detectors, and the experimental goal is to conduct signal yield measurements for low-energy neutron interactions.
In this contribution I will describe detector with associated equipment, introduce the data analysis and the pulse identification algorithm, and present results from the calibration runs and first measurements with a neutron generator. In particular, I will show systematic measurements of such fundamental parameters as electron drift velocity and nuclear/electronic recoil discrimination at various electric fields, comparing these to literature values.
Numerous observations show that most of the matter in the Universe is in a form of non-luminous, cold, collisionless, non-baryonic dark matter. One candidate under study is a stable weakly interacting massive particle (WIMP).
Liquefied-noble-gas-detectors are now among the technologies at the forefront of WIMP direct detection experiments, looking for its interactions with nuclei.
In a dual-phase LXe time-projection-chamber such in XENON1T, a particle interaction creates both primary scintillation photons and ionization electrons.
The energy scale is based on these signals and consequently a precise calibration is of prime importance. In this talk I will present the calibration steps made to allow XENON1T leading the research of dark matter.
GERDA searches for neutrinoless double-beta decay of Ge76. The liquid argon (LAr) filled cryostat containing the enriched germanium detectors is instrumented with photomultiplier tubes (PMTs) to detect LAr scintillation light, thereby vetoing background events. Currently employed PMTs are not directly sensitive to this wavelength: instead it is shifted to their sensitive region using wavelength shifters. A new Hamamatsu PMT type with a MgF2 window is transparent to this wavelength without shifters, potentially allowing material reduction, vital for low-background experiments. We present measurements of one such PMT, including gain, dark current, and afterpulse rate (at room temperature and cooled with nitrogen), with respect to long-term tests in nitrogen and LAr.
The Cherenkov Telescope Array (CTA) is the next generation of ground-based gamma-ray astronomy from 20 GeV to 300 TeV. SST-1M is one of the proposed small sized telescope for the Southern array exploring energies from 3 TeV to 300 TeV.
SST-1M camera is composed of SiPM sensors. The sensors together with front-end electronic are designed to meet CTA requirements. The camera readout and trigger system (DigiCam) is made of latest field programmable gate array (FPGA) for high throughput, high flexibility and dead-time free operation.
Special emphasis on the commissioning results will be presented with the latest performance validation tests such as charge resolution, trigger efficiency together with Monte-Carlo comparison.
The goal of the TT-PET project is to develop a compact Time-of-flight PET scanner with 30 ps time resolution, capable to stand high magnetic fields and to be integrated in traditional MRI scanners.
The TT-PET scan can achieve its very precise timing thanks to SiGe amplifiers, which are embedded in monolithic silicon sensors, which substitute the traditional high density crystals.
The scanner will be composed of 16 detection towers arranged in a ring structure. A Tower is composed of 60 modules stacked on top of each other.
A general overview of the project and readout DAQ, with its trigger system will be presented.
We present a new method of spectroscopy, utilizing a drift effect to disperse charged particles in a uniformly curved magnetic field. The curved field results in a drift of the charged particles perpendicular to the radius of the curvature and to the magnetic field, which is proportional to the particle’s momentum. A spatial-resolving detector will determine the momentum spectra.
The first realization, called NoMoS (Neutron decay prOducts MOmentum Spectrometer), will measure correlation coefficients in free neutron beta decay to test the Standard Model of particle physics and to search for physics beyond. Currently, the focus is on the design and the construction of the magnet system.
The SHiP experiment is a new fixed target experiment at CERN which aims to search for long living very weakly interacting particles. A prime example of these Hidden Particles are sterile neutrinos,
which might be produced in decays of charm and beauty hadrons.
To search them, high intensity beams are needed. The main experimental challenge is to keep a low background level. Background induced by muons coming from light meson decays can be reduced by using sweeping magnets,
while the neutrino induced background can only be reduced by using veto systmes and offline analysis. The optimization of the muon shield and the estimates of neutrino induced background will be discussed.
A novel laser based Transient Current Technique (TCT) to probe the charge transport properties of single crystalline Chemical Vapor Deposition (sCVD) diamond sensors will be presented. In this method the laser beam enters the diamond through a polished edge (hence Edge-TCT or E-TCT) and is focused inside the bulk at a known position. The dimensions of the focus point limit the size of the voxel in which charge carriers are produced by multi-photon absorption. A data acquisition system records the time-dependent current response of the drifting electrons and holes. This allows probing the electric field and charge carrier movement inside the bulk in a way that was not possible before.
The Bern cyclotron, used for production of medical radioisotopes, also features a beam-line dedicated to physics research, a unique setup in Europe. An irradiation facility was established there for campaigns with 18 MeV protons. The energy spread is 2% over an adjustable beam size up to $2x2cm^2$. The beam current can be varied and monitored between $\sim1$ pA and 150 $\mu$A, whereas also the integrated dose is determined. A movable stage allows to irradiate samples of up to a size of $20x20cm^2$. In this talk we present the facility as well as applications, like the irradiation of novel pixel sensors for new tracking detectors for the HL-upgrades of the LHC.
The First G-APD Cherenkov Telescope (FACT) is pioneering the application of solid state photo detectors for imaging atmospheric Cherenkov telescopes. Since October 2011, the FACT collaboration has successfully been showing the application and reliability of silicon photo multipliers (SiPMs) for earth-bound gamma-ray astronomy. FACT is an ideal instrument to monitor bright and variable TeV Blazars on the northern sky. Due to a quick-look analysis several flare alerts were sent to the Multiwavelength Community. Monte Carlo simulations of the system could recently be improved and show a good understanding of the SiPM's properties. The simulations fit the measured data even on proton shower level.
In the last years, intriguing hints for lepton flavour universality violating New Physics in B decays has been discovered. Including the most recent measurements, the global significance is now above the 5 sigma level.
In this talk I first review the experimental and theoretical status of these anomalies. Afterwards, I discuss various explanations in terms of New Physics models and examine the interplay with the anomaly in the anomalous magnetic moment of the muon and with direct LHC searches.
The idea that the different generations of charged leptons interact in the same way, a concept known as lepton universality, is deeply enshrined in the Standard Model of particle physics. Decays of beauty hadrons are particularly interesting tools to test for violations of lepton universality. I will review the latest lepton universality tests with semileptonic beauty quark decays, which hint at possible contributions from new particles that are not predicted in the Standard Model.
The family of decays mediated by b->sl+l- transitions provides a rich laboratory to search for effects of physics beyond the Standard Model. In recent years LHCb has found hints of deviations from theoretical predictions both in the rates and angular distributions of such processes. In addition, hints of lepton flavour non-universality have been seen when comparing B+->K+mu+mu- and B+->K+e+e- decay rates, with the so-called RK ratio. Similar observables, such as RK = BR(B0->K0mu+mu-)/BR(B0->K*0e+e-), have recently become available and indicate the same anomalous pattern. In this talk, an overview of the latest results and further avenues to test lepton flavour universality will be presented.
Charmless $b$-hadron decays are good probes to test the Standard Model and search for New Physics. Of particular interest are the $B^0_s$ decays to final state with light resonances ($\eta$, $\eta^{\prime}$ or $\phi$) that can be used for time-dependent CP violation studies. The ``golden'' $B^0_s \to \phi\phi$ mode has already been used by LHCb to measure the CP-violating phase difference between the $B^0_s$ mixing amplitude and the $b\to s\bar{s}s$ decay amplitude. We present the results of the search for the yet unobserved $B^0_s \to \eta^{\prime}\phi$ decays using the full data sample from LHCb Run1, as well as prospects for the other modes of this family using the LHCb Run2 data.
Radiative decays of $B$ mesons are flavour-changing neutral current processes used as probes for new physics (NP). They occur predominantly via $b \rightarrow s \gamma$ loop diagrams in which the photon is expected, in the Standard Model, to be mostly right handed. However, a significant left-handed component could arise from NP phenomena. The LHCb collaboration is attempting to measure the photon polarisation parameter $\lambda_\gamma$ via several methods. We present here a promising way to access this quantity through a full five-dimensional amplitude analysis of $B^{+} \rightarrow K^+ \pi^- \pi^+ \gamma$ decays using data collected with the LHCb detector from 2011 to 2016.
A search for Strongly and Electroweakly produced SUSY in final states containing opposite sign dileptons, jets and large missing transverse momentum, using 35.9 fb-1 of proton-proton data collected with the CMS detector in 2016.
The analysis uses the invariant mass of the lepton pair, searching for a kinematic edge or a resonant-like excess compatible with the Z boson mass. The search for a kinematic edge targets strong production while the resonance search targets both strongly and electroweakly produced new physics. The observations in all signal regions are consistent with the expectations from the standard model, and the results are interpreted in the context of simplified models of supersymmetry.
Naturalness arguments for weak-scale supersymmetry favour relatively light third generation squarks, which are expected to be abundantly accessible at the LHC energies. Results of a search for the light supersymmetric top with the full 2015-2016 ATLAS dataset (36.1 fb$^{-1}$ at $\sqrt{s} =\text{13 TeV}$) is presented. The search is focused on direct production of top-squark in events with two leptons of opposite charge, jets and missing trasverse energy. Four possible decay modes of the top squark are targeted with dedicated selections.
Since no excess is observed above the Standard Model background predictions for any selection, the results have been used to constrain the SUSY parameter space, extending significantly the previous results.
A search for supersymmetry in fully hadronic final states with large transverse momentum imbalance, as measured through the $M_{T2}$ variable, is presented. The results are obtained from pp collisions at $\sqrt{s}=13$ TeV corresponding to an integrated luminosity of 35.9 fb$^{-1}$ collected by the CMS experiment at the LHC. No excess above the standard model background has been observed and limits are set on the masses of potential new particles for a range of simplified models of supersymmetry.
We exploit the large W production at LHC run-2 to perform the first ATLAS search for right-handed neutrinos in the mass range 3-30 GeV. We probe unexplored regions of mixing strengths in which right-handed neutrinos can explain neutrino masses and matter-antimatter asymmetry and feature decay lengths of 1-100mm, providing the striking signature of a displaced decay. The prompt lepton from the W decay is used for triggering. To reduce backgrounds to negligible levels, we select displaced vertices outside of regions of dense material which contain two leptons. While the data are not yet uncovered, we present the discovery potential obtained from full simulations, as well as data-driven-estimate of the backgrounds.
A search is presented for single production of a heavy vector-like quark (VLQ) B in its full-hadronic decay channel: $B \rightarrow bH(\bar{b}{b})$. Higgs-tagging methods and jet substructure techniques are employed to identify decay products of boosted Higgs boson and to discriminate signal-like events against multijet background. Signal sensitivity is also enhanced by the identification of forward jets, as their presence is a peculiar feature of VLQs single production signature. The search is performed using proton–proton collision data at $\sqrt{s}$ = 13 TeV, collected by the CMS experiment at the Large Hadron Collider in 2016 and corresponding to an integrated luminosity of 35.9 fb$^{−1}$.