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The next annual meeting will take place from 27 - 30 June 2022 at the Université de Fribourg (UniFR). Renowned invited speakers will give talks in the plenary session, parallel sessions will allow in depth discussions in several topical fields, and a poster exhibition will complement the scientific program.
This program is further enriched by the direct contributions of the Swiss Institute for Particle Physics (CHIPP), the NCCR Bio-Inspired Materials, and the Swiss Neutron Science Society (SGN). Thanks to all these collaborations, our annual meeting will offer again an exciting program, covering latest advancements of physics in a wide range of fields at its best.
On 1 July 2022 the satellite event "Women in Physics Career Symposium" will take place.
NEW: Schedules and Program Overview
Registration Deadline: Extended until 10 June 2022
Note: With submitting an abstract you are NOT automatically registered. Use the registration form to do so.
Nanophotonics, which excels at controlling light in sub-wavelength volumes and providing enhanced light-matter interactions, is opening up unprecedented opportunities in many fields including biology. Our laboratory has world-leading expertise in experimental nanophotonics and its application to biosensing, spectroscopy and bioimaging by combining novelties of nano-scale optics with microfluidics, nanofabrication, biochemistry and data science. We introduce powerful bioanalytical technologies enabling label-free, real-time, and high-throughput analysis of biomolecules, pathogens and living cells for life science research, disease diagnostics and point-of-care testing. In this talk, I will present some of our recent work and provide their prospects in biomedical and clinical applications.
The Cherenkov Telescope Array Observatory construction has started and the first large size telescope is taking data since years at La Palma, Canary Islands, while three more are being built. CTAO will have a leading role in multi-messenger astrophysics, offering a view on the most powerful accelerators of the Universe. A full picture requires the combination of information from different messengers. We are witnessing in these years the many discoveries with gamma-rays from space by Fermi, the evidences of the IceCube neutrino sources and of the small-scale anisotropies by Pierre Auger with ultra-high energy cosmic rays. The future is bright for CTAO and its current status will be illustrated.
P-cubed, currently in development at Paul Scherrer Institut (PSI), is the proposed proof-of-principle experiment for the Future Circular Collider (FCC-ee) positron source. Capture and transport of the secondary positron beam released by the production target is a key challenge. P-cubed main goal is the test of a high temperature superconducting (HTS) solenoid as adiabatic matching device (AMD) for the initial focusing of the positrons. Beam dynamics simulations show considerably higher positron yield with respect to the state of the art. The experiment aims at validating this expectations, taking advantage of the available 6 GeV electron beam of SwissFEL, which will be used as drive beam for the positron generaion.
Reaching the ultimate field for Nb3Sn conductor in accelerator magnets in a robust (industrializable) and cost-effective manner is the goal of an international effort, centered around the specifications for the FCC-hh main dipoles. While conductor R&D makes steady progress towards FCC-hh specs, the experimental effort on high-field magnets in Europe is ramping up. CHART MagDev has recently reached an important milestone, allowing for the selection of the most promising technologies of an innovative Nb3Sn magnet. The concept combines novel materials with stress-management and simplified manufacturability. In this presentation we present R&D results, as well as the design concept that will be implemented and refined over the coming years.
No-insulation HTS ReBCO solenoids have been studied in numerous laboratories and commercial entities over the past years. The CHART MagDev project, in collaboration with Tokamak Energy Ltd. and CERN, is studying the solder-impregnated NI-coil variant. The goal is to provide an Adiabatic Matching Device for the positron source of the CHART FCC-ee Injector test stand ad PSI’s SwissFEL. In this presentation we show recent results from our technology R&D, discuss test results from our recently commissioned 2-kA cryogen-free test station, as well as the technical design of the AMD device to be constructed in the coming years.
The FCC-ee is one of the main candidates to succeed the HL-LHC at the forefront of particle physics and will require extensive simulation campaigns. A new collaborative project between EPFL and CERN aims to develop modern and maintainable simulation tools to address the key challenges of the FCC-ee. This talk presents an overview of the project as well as the first developments and results. This includes a new lattice management tool that has been developed to facilitate the manipulation of accelerator lattices and integrate conversions to different simulation codes. These developments have already sparked new efforts in FCC-ee studies in the field of collimation, tuning and spin dynamics.
Resonant depolarization measurements offer a promising method for the high
precision center-of-mass energy calibration that can be applied in the FCC-ee.
Simulations need to be performed to validate the obtainable polarization limits
under the influence of perturbed orbits. This study offers the first exploration
of the FCC-ee spin polarization simulations using Bmad. The relations between
the linear polarization limits and the energies under different conditions have
been investigated. The results of benchmarks with SITROS as well as the results
of nonlinear spin tracking using the Long Term Tracking module in Bmad are
presented.
The FCC-ee (Future Circular Collider) lepton collider is currently the most favored next generation research infrastructure project at CERN, aimed at studying properties of standard model particles with the highest precision ever.
The chosen parameters of the machine yield unprecedented conditions which give rise to previously unseen dynamical effects during collisions. The exploration and understanding of these beam-beam effects is of crucial importance for the success of the FCC-ee feasibility study. To address this challenge, a new general purpose software framework for beam dynamics simulations is currently under development at CERN. This presentation will discuss the contributions to the software development related to beam-beam effects with benchmarks studies and applications.
An 18-MeV-proton beamline is available for research activities at the Bern University Hospital's medical cyclotron. This talk will focus on its application as an irradiation facility for radiation hardness tests, targeting instrumentation for particle physics experiments and space missions. An overview of the facility's capabilities, including its on-site characterization laboratory, as well as ongoing R&D projects in beam instrumentation, will be given. Finally, an innovative project will be presented in which it is intended to produce a controlled neutron beam for radiation hardness tests, through conversion of the primary proton beam using targets of different materials.
Currently PSI delivers the most intense continuous muon beam in the world with up to few 10^8 μ+/s. The High Intensity Muon Beam (HiMB) project aims at developing a new target station and muon beam lines able to deliver up to 10^10 μ+/s, with a huge impact for low-energy, high-precision muon based searches.
This is done by boosting the surface muon production efficiency with a new target geometry and increasing capture and transmission with a solenoid-based beam line. The latter affects also the rates of the other particles produced at target making the beam lines suited also for non-surface muon beams. We present the current status of the HiMB project.
A key issue in controlled thermonuclear fusion research is to predict and optimize the plasma behavior in the reactor core. In this work, we use the RAPTOR code, a fast and light simulator of the current density and heat 1D radial transport equations, to identify future scenarios for tokamak discharges. To do so, a first phase is needed where we aim to improve the robustness and flexibility of our model, comparing results with experimental datasets and minimizing the need for user specification and experimental measurement. The final goal is to perform simulation and optimization of whole plasma discharges both before (pre-shot) and during (real-time) experiments.
Sustainability has become an important aspect of all human activities, including the operation of research infrastructures. This presentation will review the power efficiency and related R&D efforts of accelerator concepts and technologies. The three main categories proton driver accelerators, light sources and particle colliders will be considered. Several technologies are particularly relevant for power efficiency of those facility types. These include superconducting RF and cryogenic systems, RF sources, energy efficient magnets, conventional cooling, heat recovery. Power efficiency has been a topic in the European programs EUCARD-2, ARIES and the ongoing I.FAST, and reference is made to these programs.
Radioisotopes for theranostics are essential for nuclear medicine developments. A research program is ongoing at the 18 MeV Bern medical cyclotron, equipped with a solid target station and a 6 m long Beam Transfer Line ending in a separate bunker. To bombard compressed powder pellets, novel target coins were conceived and realized together with methods to assess the beam energy and the production cross-sections. The EoB-activity is measured with a CdZnTe detector. An ultra-compact active irradiation system based on a novel magnetic lens and two-dimensional beam detectors is under development. Results on Er-165, Tm-165, Tm-167, Tb-155, Ga-68, Cu-61, Cu-64, Sc-43, Sc-44 and Sc-47 production are presented.
Directed self-assembly (DSA) of block copolymer is a promising approach to achieve macroscopic ordered nanostructures. Here, we investigate the combined effect of solvent vapour annealing and chemical topographical guiding patterning on the self-assembly and grain size of a 3D diamond-forming triblock terpolymer Polyisoprene-block-polystyrene-block-poly(glycidylmethacrylate) (ISG). The guiding patterns were designed according to specific lattice diamond planes (110). In order to gain some chemical contrast, the patterns were fabricated out of hydrophilic silica lines or hexagonal dots on top of a less hydrophilic gold background. Our results show that, depending on the design of the substrate guiding patterns, the polymer will microphase separate in 2D lamellae or 3D diamond morphology forming a single domain on top of the patterned area (16 x 16 µm).
The membranes of living cells form excellent barriers, separating the cell contents from the outside environment, while only several nanometers thick and spanning large areas. Inspired by these biological membranes, we present the formation and characterization of amphiphilic block copolymer membranes. We demonstrate that these polymers can form membranes of less than 20 nm in thickness over areas approaching 1 cm2 between two non-mixing aqueous phases, potentially making them the largest of their kind. Moreover, the membranes allow incorporation of selective ion carriers or channels, thus displaying diode behavior when using different ions in the two aqueous phases.
Within the context of the European Horizon 2020 project ACDC, we intend to develop a probabilistic chemical compiler, to aid the construction of three-dimensional agglomerations of artificial hierarchical cellular constructs. These programmable discrete units offer a wide variety of technical innovations, like a portable biochemical laboratory that e.g. produces macromolecular medicine on demand. For this purpose, we have to investigate the agglomeration process of droplets and vesicles under proposed constraints, like confinement. In this talk, we focus on the influence of the geometry of the initialization and of the container on the agglomeration.
The work presented here demonstrates that plasmonic optical tweezers can reveal insights into the conformational dynamics of native proteins that so far have not been investigated on a single molecule level. We examined citrate synthase , an enzyme of the Krebs cycle, which consists of two identical subunits with one active site per subunit. Previous studies show that during catalysis, each subunit of the enzyme independently closes upon substrate binding and opens for product release and renewed substrate binding. Our approach reveals that during the enzymatic cycle, the subunits of citrate synthase populate a previously unknown, intermediate conformation that is crucial for enzyme activity.
Solid state nanopores enable the analysis of single biomolecules in solution. Here we present a simple, in situ method for coating silicon nitride nanopores that addresses three of the main challenges in the field. By adding polymer directly to the recording buffer we were able to i) reduce non-specific interactions of the analyte with the pore; ii) suppress growth of the pore in electrolyte; iii) use nanopores on glass chips with superior noise properties for high bandwidth recordings.
Furthermore, experiments with aldolase show that the polymer des not affect the determination of protein volume.
Using RIXS and REXS, we measured the systematic modification of Cu-charge density wave in optimally doped YBa2Cu3O7, under the interfacial proximity of Nd1-x(Ca1-ySry)xMnO3 as function of the hole doping and tolerance factor of the manganite layers.
For x=0.35, we observe the Cu-CDW order with the usual dx2-y2 orbital character at Q||=0.3 r.l.u, which gets strongly enhanced as the tolerance factor of the manganite layers is decreased or when a strong magnetic field is applied.
For x=0.5 and y=0.25, we observe a completely new kind of Cu-order which has a small wave vector of Q||=0.1 r.l.u., a much larger correlation length of about 40nm and a completely different dz2 orbital character.
Tantalum disulphide (1$T$-TaS$_2$) is a layered material which hosts an insulating commensurate charge density wave (CCDW) at temperatures below ~165K. Recent investigations of 1$T$-TaS$_2$ have revealed the existence of a metastable metallic phase accessible from this CCDW phase by applying a laser- or current pulse. Here we present Scanning Tunnelling Microscopy and Spectroscopy (STM/STS) measurements on 1$T$-TaS$_2$ surfaces not exposed to such pulses which show the same metallic behaviour as the pulse induced phase over distances of hundreds of nanometres. Further analysis shows evidence of a change in top layer stacking in the metallic phase, in agreement with recent theoretical and experimental works.
The metallic kagome ferromagnet Fe$_3$Sn$_2$, which shows large spin-orbital coupling, hosts various exotic electronic/magnetic states, including flat electronic bands, massive Dirac fermions, and field-tunable nematicity. While most studies focus on the electronic degree of freedom, investigations of the spin excitations are scarce. Here we studied the character of the low-energy excitations in Fe$_3$Sn$_2$ by exploiting magnetic circular dichroism (MCD) in Resonant Inelastic X-Ray Scattering (RIXS). With the selection-rule analysis, spin-wave excitations are identified with a flat band and a dispersive acoustic band. Our results unveil the nature of the spin dynamics in Fe$_3$Sn$_2$, and present a new way to study the spin excitations in ferromagnetic materials by RIXS MCD.
RENiO3 perovskites are a handbook example of strongly correlated system, where interplay between, lattice, charge, and spin degrees of freedom leads to spontaneous metal-insulator transition. The electronic localization is associated with a charge redistribution and subtle structural distortions. Recently, intriguing phenomena like non-centrosymmetric antiferromagnetic ordering or multiferroelectricity have been theoretically predicted in the system. However, drawback for the advancement in the nickelates physics has been lack of single crystals, which limited amount of experiments, needed for validation of predictions. We achieved RENiO3 crystals by applying the solvothermal method in temperature gradient under high-oxygen-pressure, which have opened new opportunities to go beyond known up to date physics of the family.
Wide bandgap oxides (WBGOs) have exhibited superior material properties for power electronics and optoelectronics. However, transient electronic dynamics right after high-density carrier injection into the conduction band of WBGOs has not been fully understood. In this study, we achieved transient carrier injection in a simple cubic perovskite WBGO via ultrafast above-gap photoexcitation and revealed its sub-picosecond carrier dynamics across the bandgap. A fast hot-carrier cooling lifetime of 1ps due to electron-phonon scattering along with clear exciton bleach and excitonic enhancement resulting from photo-excited free carriers are unveiled. The collective carrier behaviour under many-body interactions in this study provides fundamental information to investigate the underlying physics in perovskite WBGOs.
Metal halide perovskites (MHPs) have attracted great attention in recent years due to their enormous potential for application in optoelectronic devices. However, the defects at surface/interfaces and grain boundaries of perovskite films, which impede the further enhancement of power conversion efficiency (PCE) and long-term stability of halide perovskite solar cells (PSCs), still need to be fully understood. Here, we studied the effect of different growth conditions on the interface and grain boundaries of CH3NH3PbI3 perovskite films by low-energy muSR.
TiSe2 is a transition metal dichalcogenide materials that exhibits charge density wave (CDW) phase transition below T ≈ 200 K. The CDW formation is associated to a structural distortion of the lattice into a new one whose Brillouin zone size is halved.
We present a Raman spectroscopy-based approach to determine the CDW transition temperature (TCDW) of exfoliated TiSe2 onto Si/SiO2, upon different film thicknesses.
The aim of this work is to investigate the relationship between the TCDW and the thickness of the TiSe2 flakes and to further explore its correlation with the layer number parity.
The High Energy cosmic-Ray Detection facility (HERD) is a future space-borne experiment that is planned to be launched in 2027. It will be installed on the China’s Space Station (CSS) and will collect data for at least 10 years. The detector is under development, laboratory and beam tests are performed to finalize the overall design. The scientific goals and requirements of HERD will be presented, together with the performance of the prototypes of its subdetectors.
The DArk Matter Particle Explorer (DAMPE) is a satellite-borne experiment, in operation since 2015, aimed at studying high-energy gamma rays and cosmic nuclei fluxes. The detector system comprises a plastic scintillator detector for charge measurement, a silicon-tungsten tracker-convertor for tracking incident particles, a bismuth-germanium oxide calorimeter for energy measurement and a neutron detector that further aids in hadron identification. Recently, machine learning (ML) techniques have been deployed with the aim of improving particle tracking and identification as well as compensating for the energy lost in the calorimeter at high incident energies due to saturation of the electronics. This work presents an updated helium flux after application of these ML techniques.
Gamma-ray bursts (GRBs) are one of the most energetic explosions in the universe. GRBs still have various unknown aspects such as gamma-ray emission processes and jet launching mechanisms.
Gamma-ray observations on GRBs have been performed mainly by satellite telescopes, however photon spectra in the very-high-energy (VHE) range above 100 GeV have large uncertainties due to the low statistics.
Since 2018, 4 GRBs have been detected above 100 GeV thanks to the improvement of the ground-based telescopes such as MAGIC and H.E.S.S.
In this presentation I report the analysis results of VHE data and possible interpretations of GRB 190114C and GRB 201216C detected by MAGIC.
By analysing microlensing light-curves of the multiple images of a strongly lensed quasar, one can yield powerful constraints on its structure. These light-curves are under the influence of three main variable components: the continuum flux, microlensing by stars in the lens galaxy and reverberation of the continuum by the Broad Line Region (BLR).
In Paic et al.(2022) a new method was applied to the COSMOGRAIL light curves of QJ0158-4325. We showed that the short time scale features observed are due to reverberation by the BLR. This allows us to measure, for the first time, the size of the BLR using single-band photometric monitoring in good agreement with previous estimates.
The Standard Model Effective Field Theory (SMEFT) and the Low Energy Effective Field Theory (LEFT) can be extended by adding additional spin 0, 1/2 and 1 dark matter particles which are singlets under the Standard Model (SM) gauge group. In my talk I will classify all gauge invariant interactions in the Lagrangian up to terms of dimension six, and discuss the tree-level matching between the two theories at the electroweak scale.
As an application I will consider a model with dark vector particles obeying a Z2 symmetry. This setup is a viable dark matter model in the freeze-in scenario for a wide range of parameters.
Understanding the nature of Dark Matter (DM) is one of the open issues of modern physics. In this context, the XENON project aims to lead the effort on DM direct detection using a ton-scale xenon dual-phase time projection chamber. The status of the XENONnT detector, currently acquiring data in a low background environment at LNGS (L'Aquila, Italy), is presented. The preliminary results of the experiment will be discussed, as well as its broader science goals.
The nature of dark matter is one of the big unknowns of our present time. Despite abundant gravitational evidence of its existence, it has so far eluded detection in particle form. Building upon established detector technologies, the DARWIN experiment will utilise liquid xenon as target to search for dark matter interactions with Standard Model particles. Its ultra-low background and 40-tonne mass will open new parameter space for WIMPs and other dark matter candidates. DARWIN's unprecedented sensitivity will also provide potential for neutrino physics and enable its use as a solar observatory. In this talk I will describe the experiment, science program, and status of the next-generation dark matter detector.
The DARWIN observatory is a proposed multi-purpose experiment for dark matter and neutrino physics, featuring a 50 tonne (40 tonnes active) dual-phase xenon time projection chamber. To test key technological concepts required for the realization of DARWIN, we built Xenoscope at the University of Zurich, a full-scale vertical demonstrator using 350 kg of liquid xenon (LXe). It will be used as a first-time demonstration of electron drift in LXe over 2.6 m, as well as to study electron cloud diffusion and measure LXe optical properties. We present an overview of the Xenoscope facility, its commissioning, as well as current and future measurements.
“Climate change is physics”; this was highlighted by the 2021 Nobel Prize in Physics. Physically based models of the atmosphere and ocean, which have been developed since the mid 1960s, have predicted fingerprints of climate change that we now observe worldwide. Warming in the troposphere and cooling in the stratosphere, warming of the ocean, and the accelerating melting of glaciers and polar ice sheets leading to sea level rise are testimony to these changes that are unprecedented in human experience. In this lecture we recall some of the seminal research of two of the three laureates of the Nobel Prize in Physics 2021, and put them into the broader context of climate research carried out in physics. Taken together, the physical science basis has been essential, not only for the UN Framework Convention on Climate Change but also for the Paris Agreement.
Even though most of us tie our shoelaces 'wrongly,' knots in ropes and filaments have been used as functional, structural mechanisms for millennia in sailing, climbing, and surgery. Still, knowledge on physical knots is mostly empirical, and there is a need for physics-based predictive models. For tight knots, highly nonlinear and coupled behavior arises from the intricate 3D geometry, large deformations, (self)contact, and friction. Furthermore, tight knots do not exhibit separation of the relevant length scales, precluding the usage of centerline-based rod models. Our precision experiments using X-ray computed tomography and mechanical testing have yielded unprecedented data, which we contrast to Finite Element simulations and analysis of ideal (geometric) strings. Building on this understanding, we have been collaborating with a surgeon to characterize, analyze, and rationalize the physics of surgical knots. These findings could have potential applications in the training of surgeons and control of robotic-assisted surgical devices.
It is a key goal of fusion research to build devices that allow us to create a plasma at sufficiently high pressure and energy confinement time, so that the conditions for a burning plasma can be met. For a long time, progress along these lines was largely based on a "trial-and-error" approach. With the preparation of ITER operation and attempts to design first versions of future fusion power plants, it became clear that a more targeted "predict-first" approach is needed to accelerate the further development of fusion energy. Modern supercomputers open up new possibilities to solve the complex underlying equations, allowing us to move from an interpretative to a truely predictive approach. So how and when will we be able to predict plasma confinement in fusion devices?
Engineering strong interactions between quantum systems is essential for many phenomena of quantum physics and technology. Typically, strong coupling relies on short-range forces or on placing the systems in high-quality electromagnetic resonators, which restricts its range to microscopic distances. We used a free-space laser beam to strongly couple an atomic ensemble and a micromechanical membrane over 1 meter distance in a room-temperature environment. The coupling is highly tunable and allows the observation of normal-mode splitting, coherent energy exchange oscillations, two-mode thermal noise squeezing, and dissipative coupling. Our approach to engineering coherent long-distance interactions with light enables modular interfaces for quantum networks and control.
Spin-dimer systems are an ideal testbed to study criticality because a quantum phase transition from a disordered to a magnetically ordered phase can be induced by a magnetic field. To determine the spin Hamiltonians of the spin-dimer compounds BaCuSi2O6 and Ba0.9Sr0.1CuSi2O6 inelastic neutron scattering experiments are performed at zero field and the magnetic order in BaCuSi2O6 is investigated using neutron diffraction up to 25.9 T. The phase boundary of Ba0.9Sr0.1CuSi2O6 is obtained by NMR and the critical exponent is determined using Bayesian inference. Quantum Monte Carlo simulations of the phase boundaries agree excellently with the form of both measured phase boundaries.
Atomically thin transition metal dichalcogenides, such as molybdenum disulfide (MoS2), are promising candidates for opto-electronic devices because of their intrinsically strong light-matter interaction. However, excitons in monolayer MoS2 are not electrically tunable due to their limited out-of-plane extend, leading to a minimal electric dipole moment. We engineered a tunable system using bilayer MoS2 in a gated van der Waals heterostructure, where the vertical separation of the electron and hole leads to a large dipole moment. By applying a voltage to the electrodes, we generated an electric field that tunes the absorption of the two MoS2 layers. This approach combines the large oscillator strength with high electrical tunability.
Recent advances in signal processing enable the fundamentally faster measurement of the current-voltage characteristic for tunneling spectroscopy through the parallel demodulation of higher harmonics that are produced from nonlinearities in the tunneling junction. The local density of states (LDOS) can thus be measured in a few milliseconds. Here, we use the fast spectroscopy for quasiparticle interference imaging not only at a fixed tunneling impedance but also measure the LDOS for varying tip-sample separations. From the tip-height dependent I-V measurements, we obtain voltage dependent decay length measurements in an energy interval previously inaccessible.
The discovery of ferromagnetic 2D van der Waals (vdW) crystals allows the study of novel magnetic phenomena at a reduced dimensionality. While exfoliated 2D vdW crystals offer only limited control of their exact geometry, 2D magnets grown by molecular beam epitaxy (MBE) overcome this limitation. Here, we investigate the MBE grown 2D in-plane ferromagnet EuGe$_2$ on a nanostructured substrate by quantitative scanning nitrogen-vacancy magnetometry. We determine its fundamental magnetic parameters quantitatively in various geometric configurations and offer new insights into the transition from bulk properties to the 2D limit. Moreover, we provide the basis for targeted engineering of geometries to nucleate novel spin-textures and domain patterns.
The growth of thin films and nanostructures on solid surfaces is governed by the substrate structural properties and lattice matching. In this respect, metallic alloys can offer an interesting alternative to conventionally utilized pure metal substrates due to a larger flexibility in the effective lattice parameter. In our work we investigate the structural and electronic properties of Cu3Au(111) surface by means of STM and nc-AFM. Furthermore, we demonstrate the crystal’s potential as a substrate for the growth of cobalt islands as an alternative to Co/Cu(111), for which we explore their structure and characterize their magnetic properties.
Layered van der Waals chromium trihalides have received growing interest in recent years due to their extraordinary electronic and magnetic properties as well as the opportunity for the development of future functional heterostructures. We investigate the electronic configuration of CrI$_{3}$, CrBr$_{3}$, and CrCl$_{3}$ by Resonant Inelastic X-ray scattering (RIXS). The temperature-dependence of the RIXS response displays the correlation between the magnetism and the electronic configuration across the magnetic transition. From charge-transfer multiplet calculations, we quantify crystal-field and the evolution of the spin-state. The spin-state transition of Cr$^{3+}$ is strongly coupled to changes in orbital-selective Coulomb correlations controlling the spin-orbital excitations.
We present a combined broadband transient reflectivity and femtosecond X-ray emission spectroscopic study of spinel Co3O4, a system representing a prototypical case of the intrinsic complexity of transition metal oxides, due to its correlated interaction of electronic, nuclear and spin degrees of freedom.
By exciting the ligand-to-metal charge transfer and metal-to-metal charge transfer transitions of the system, we show excitation-specific coherent and incoherent photoresponses that are mediated by different electron-phonon couplings and involve distinct Cobalt electronic transient configurations.
Our joint investigation rules out a stepwise cascade mechanism in the charge carrier relaxation of the material, and it presents a radically different picture compared to previous time-resolved studies of Co3O4.
The ultra-strong coupling between the cyclotron resonance of a 2D electron gas in a static perpendicular magnetic field and an antenna-based metamaterial that can sustain chiral electromagnetic modes gives rise to polaritonic states with opposite circular polarizations, thus providing a way to break time-reversal symmetry. To further investigate polaritons dressed by the electromagnetic vacuum in the cavity, highly subwavelength interacting volumes along with high electron densities are needed. Therefore, planar cavities on a GaAs/AlGaAs heterostructure are engineered and characterized through THz time-domain spectroscopy, and the coupling mechanism and its limitations are understood straightforwardly via classical circuit theory.
We describe the design and characterization of using a NbFeB permanent magnet system to retrofit existing experiments with a magnetic field around 200mT. The design is compatible with UHV high-temperature sample cleaning routines which are normally above the Curie temperature of a permanent magnet.
We characterize the flux density distribution with superconducting vortices in NbSe2 and BSCCO and demonstrate the life-cycle of the magnet from sample preparation to characterization.
Our magnet provides an accessible way to field-dependent surface science studies, ranging from vortices in high-temperature superconductors to STM-enabled electron spin resonance.
The two-dimensional electron gas (2DEG), formed at the surface/interface of oxide insulators, exhibits exotic physical properties. The modulation of electronic structures of 2DEG system are of crucial importance to control the properties. In this report, I will introduce the ARPES results on two 2DEG systems. (1) In amorphous LaAlO3/LaMnO3/SrTiO3, the LaMnO3 buffer layer significantly suppresses the formation of oxygen vacancies, and the electron-phonon interaction is reduced, explaining the mobility boost in this system. (Published on ACS Nano) (2) On SrTiO3 surface, we discovered band modulations with in-situ sputtering-annealing, and a robust single-band 2DEG states. Meanwhile, the possible origination and mechanisms of light-induced 2DEG on SrTiO3 surface are also discussed.
To unveil mobile excitons we use angle-resolved photoemission spectroscopy (ARPES) to detect dispersing excitons in the quasi-one-dimensional metallic trichalcogenide TaSe3. While screening usually suppresses exciton formation in metals, the low density of conduction electrons, the low dimensionality, and two many-body effects favor them. In this presentation I will introduce the idea how to use ARPES to detect dispersing excitons in the quasi-one-dimensional metallic trichalcogenide. We show that the interplay of dilute conduction electrons, low effective dimensionality, and heavy quasiparticles seems to result not only in a single excitonic branch of excitations, but even in multiple “sidebands”, suggesting the possibility of creating bound states with different internal structure.
Systematic strain studies with ARPES have long been notoriously difficult to achieve. Here, we report first results from strained Sr$_2$RuO$_4$ using a novel technique combining a thermally-actuated strain cell with a micro-structured tapered sample prepared by focused ion beam milling. For the first time, this allows the quasi-continuous variation of strain on a single sample. I will explain our new technique and present results demonstrating the quasi-continuous tuning of a van Hove singularity across the Fermi level. I will further discuss the evolution of the spectral function near van Hove strain where transport experiments found signatures of non-Fermi liquid behaviour.
The recently discovered layered kagome metals AV${_3}$Sb${_5}$ (A=K, Rb, Cs) exhibit diverse correlated phenomena, which are intertwined with a topological electronic structure with multiple van Hove singularities (VHSs) in the vicinity of the Fermi level. As the VHSs with their large density of states enhance correlation effects, it is of crucial importance to determine their nature and properties. In this talk, we will introduce the rich nature of the VHSs and the sublattice properties of 3d-orbital VHSs in CsV${_3}$Sb${_5}$. The crucial insights into the electronic structure, revealed by our ARPES measurements, provide a solid starting point for the understanding of the intriguing correlation phenomena in the kagome metals AV${_3}$Sb${_5}$.
RENiO3 (RE - Rare Earth elements) exhibit multifunctional physical phenomena related to the spin and orbital degrees of freedom of the transition metal d-states and their interplay with the lattice. Notably, the iso-structure of RENiO3 permits the realization of hetero-structures altering physical matters that are very different from their bulk form.
Our ARPES data demonstrates that substrate-induced strain tunes the splitting of the crystal field, consequently changing the Fermi Surface (FS) properties and thereby controlling the Metal-Insulator Transition (MIT). Furthermore, our comprehensive study discloses the direct magnetic coupling between the NNO film and the manganite layer in proximity, causing the new magnetic phase in nickelates.
In Fermi liquids, electron-boson coupling is (EBI) quantified through the Eliashberg function $\alpha^2F(\omega,\mathbf{k})$, which modifies their self-energy $\Sigma(\varepsilon,\mathbf{k})$ obtainable from ARPES. We present a combined ARPES, density-functional theory, and high-resolution electron energy-loss spectroscopy (HREELS) study on the EBI in CaTiO$_3$ (CTO) thin films. CTO hosts a 2-dimensional electron liquid (2DEL) analogous to that in SrTiO$_3$-based surfaces, making both materials technologically appealing for oxide electronics. Our results show that the presence of localized in-gap states changes the dielectric response of the CTO film, red-shifting high-energy phonon modes, thereby indicating their strong coupling to the 2DEL states. Combining ARPES with HREELS is a powerful approach to study quantum materials with strong EBI.
Recent transport experiments revealed a correlated insulating phase and quantum criticality points in twisted transition metal dichalcogenides (TMDs) that were predicted to host non-dispersive Moiré mini-bands. Here, we report for the first time on the direct observation of flat bands in twisted TMDs investigating 57° twisted bilayer WSe$_2$ by micro-focused angle-resolved photoemission spectroscopy. We resolve multiple Moiré mini-bands with strongly reduced dispersion and significant mini-gaps. By comparison with effective continuum band structure models, we attribute the origin of the flat states to a moderate Moiré potential of ≈ 50 meV emerging from the stacking of the two semiconducting layers.
This work focuses on modulation of spin-orbit interaction (SOI) in 2H-MoSe2 induced by proximity effects at its interface with amorphous Pb, providing strong SO coupling. The key element of our approach is the formation of amorphous Pb overlayers, allowing us to overcome k-space mismatch of the wavefunctions across the interface. We use SX-ARPES, which allows reaching the interface region where the SOI is modulated. Definition of the out-of-plane electron-momentum in the SX-ray energy region enables determination of the proximity-induced SOI through the full 3D k-space and its dependence on the Pb-overlayer thickness. Analysis of the experimental data are supported with one-step ARPES calculations based on the multiple scattering GF-KKR method.
Misfit compounds are natural stacks of two-dimensional materials, forming a three-dimensional structure that is commensurate in one direction but incommensurate in the other. Here we show that the misfit structure can be used to strongly influence the electronic properties as in an artificial moire structure formed from two-dimensional materials. Using ARPES with a micron-scale light focus, we selectively probe the electronic properties of NbSe2 and BiSe layers that form the (BiSe)1+δNbSe2 misfit compound. We show that the BiSe band structure is affected by the presence of the NbSe2 layers, leading to a quasi one-dimensional electronic structure. This lattice-induced band structure modification opens a rich way to designing novel electronic states.
YNi$_2$B$_2$C is a borocarbide superconductor with a complex electronic band structure that has a very strong Ni character near the Fermi energy. We present density functional theory (DFT) and one-step model of photoemission results for YNi$_2$B$_2$C and compare them to experimental soft x-ray angle resolved photoemission spectroscopy (SX-ARPES) measurements.
We show that electron correlations have to be included, using dynamical mean field theory (DMFT) applied to the Ni d-states, to reach the best agreement with experiments. One-step model calculations are essential to ensure the comparison between DFT and ARPES.
Recents hints of lepton flavour universality violation in b-hadron decays suggest that the rates for lepton flavour violating decays may be much higher than predicted in the Standard Model.
With its large number of recorded b-hadron decays, the LHCb experiment is ideally suited for the searches for lepton flavour violation due to its large acceptance, high trigger efficiency and excellent tracking and particle identification capabilities.
In this talk, the analysis strategy and status for the search for the lepton flavour violating decays of B0s→e±μ∓ and B0→e±μ∓ using Run 2 data collected by the LHCb experiment will be presented.
Using analytic results obtained in a meson effective theory which includes all infrared sensitive logs, we build a dedicated Monte Carlo to describe QED corrections in $\bar{B}^{0} \rightarrow \bar{K}^{0} \ell \ell$ processes.
We present a detailed numerical comparison of the impact of QED corrections in our framework with respect to the ones obtained when simulated using the general-purpose photon-shower tool PHOTOS. In addition, our framework allows us to study the impact QED corrections in interference effects between the rare mode and the charmonium resonances.
The family of decays mediated by $b \to s \ell^+ \ell^-$ 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 in lepton flavour universality (LFU) testing branching fraction ratios (i.e. $R_{K}$, $R_{K}^{*}$), and in the angular distribution of the $B^{0}\rightarrow K^{*0}\mu^{+}\mu^{-}$ decay. The angular analysis of the electron mode allows for the investigation of LFU in angular distributions, and the potential formation of an experimental link between those two sets of anomalies. In this talk, I will discuss the status of the angular analysis of $B^{0}\rightarrow K^{*0}e^{+}e^{-}$ decays at the LHCb.
Forward electrons in proton-proton collisions at the LHC are promising signatures for finding new physics beyond the Standard Model. The ATLAS detector is not equipped with precision tracking in the pseudorapidity range of $\eta$ larger than 2.5, where electromagnetic and hadronic end-cap and forward calorimeters are still providing information. Machine learning techniques are used to distinguish electromagnetic from hadronic showers and the performance of the Neural Ringer algorithm identifying forward electrons with $2.5<\eta<3.2$ at the ATLAS High Level Trigger will be shown.
The coupling of electroweak gauge bosons to the three lepton families is universal in the Standard Model (SM). Possible extension of the SM do not necessarily have this property. Rare decays of heavy flavour particles may be affected by sizeable contributions in presence of New Physics which is not lepton universal. The precise study of such decays with B hadrons allow for a stringent test of the lepton universality in the SM. The recent experimental results from LHCb on lepton flavour universality in rare b-> sll decays are discussed as well as prospects for such measurements in the coming years.
Mu3e is a dedicated experiment to search the rare charged lepton flavor violating (cLFV) decay $\mu^{+} \rightarrow{} e^{+}e^{-}e^{+}$ with a sensitivity down to $10^{-16}$ under construction at PSI. In the Standard Model, this decay is heavily suppressed with a branching fraction of $10^{-54}$. The Mu3e experiment will be able to reconstruct low momentum electrons and positrons from rare $\mu$ decays. Mu3e apparatus consists of a tracking detector based on monolithic active pixel sensors for very precise momentum and vertex reconstruction, combined with scintillating fibers and tiles for very high timing measurements. The motivation for the $\mu^{+} \rightarrow{} e^{+}e^{-}e^{+}$ search will be presented, along with experimental design and subsequent expected sensitivity.
Mu3e is an experiment under construction at PSI to search for the lepton flavor violating $\mu \rightarrow eee$ decay at branching fractions $>10^{-16}$. Being heavily suppressed in the Standard Model, its observation would indicate the existence of new physics. Achieving such sensitivity requires a high rate of muons and a large kinematic acceptance; hence, excellent time resolution is essential to suppress the accidental background and to facilitate the global event reconstruction. In particular, the scintillating fiber (SciFi) sub-detector is designed to achieve a very precise time measurement at high efficiency and rate capability. In this talk, the SciFi design and performance is presented in the context of the Mu3e requirements.
Measurements related to the decays of semi-leptonic b hadrons, mediated by charge-current transition, allow for stringent tests of Standard Model (SM) predictions. They provide a critical tests of lepton flavour universality and help confront theoretical predictions of differential decay rates. In fact, a combination of results from LHCb, Babar and Belle concerning lepton flavour universality has shown a discrepancy from the SM prediction at the level of 3 σ, hinting at contributions from beyond the SM. The talk will review recent studies of lepton flavour universality and differential decay rate measurements of semi-muonic decays. The talk will also highlight the status of ongoing and planned measurements involving these decays.
Many Beyond Standard Model theories predict particles called leptoquarks that couple both to leptons and quarks. In addition to receiving theoretical interests, the search for these new particles has the potential to explain the recent hints in lepton flavour universality violation. This talk presents the initial steps of the search for single third-generation leptoquark from $\bar{b}b$ scattering, with $b\bar{b}$ + $\tau^-\tau^+$ final state using the full Run-2 dataset from the ATLAS detector.
PIONEER is a newly approved, next-generation precision pion decay experiment at PSI testing lepton flavour universality. Phase I aims at measuring the charged-pion branching ratio to electrons vs. muons 15 times more precisely than the current experimental result, reaching the precision of the Standard Model (SM) prediction at 1 part in 10000. Considering several inconsistencies between the SM predictions and data pointing towards the potential violation of lepton flavour universality, the PIONEER experiment will probe beyond-SM explanations of these anomalies through sensitivity to quantum effects of new particles up to the PeV mass scale. This talk will introduce the conceptual experiment design and describe the physics motivation of Phase I.
After 20 years in research in the field of particles and radiation detectors for high-energy physics in laboratory and space, the author moved to industry and is now managing a small company providing engineering services. The most appealing characteristic of a physicist in both academy and industry is the ability of solving complex problems. Complexity arises from at least few among the following aspects: conceptual context, technological challenges, long duration of project, multi-cultural nature of project team, political, societal and/or environmental implications of the results, etc. The main difference between research and industrial work is the point of view, to be elaborated further in the presentation.
This presentation provides insights from a growing physics-based business evolving around photon, charge and heat fluxes. Fluxim AG is a provider of simulation software and measurement hardware to the display, lighting, and photovoltaics community worldwide. Fluxim’s R&D tools address the needs of researchers and engineers in industrial and academic research labs for the development of emerging electronic devices and semiconducting materials. We combine expertise in numerical methods, physical modeling, software and hardware engineering and aim at boosting the R&D efforts of our customers.
ABB Corporate Research, in close cooperation with varied ABB business areas, is developing the foundations for the next generation of ABB products. R&D engineers and scientists develop new technologies and products that change the way the world works and industries do business. We constantly push the limits of convention, while retaining our focus on delivering solid returns for our customers. One of the task under current scientific investigation is the reliability of wide band gap semiconductor. Optimizing the power cycling methodology, predicting the failures before they occur together with the understanding of the threshold voltage instability implication’s in the field case are topics addressed in the presentation.
Intellectual property rights are more important than ever in this global, highly-connected digital landscape. With all of the good the rise of the internet has done for information sharing, it has become easier for ideas to be stolen, which can be damaging to both economies and innovation. Starting with a brief overview of the different types of IP rights, this talk will focus on the career opportunities for a physicist as a patent attorney working in a unique space where law, commerce and technology all overlap. The variety of work, both in terms of clients and technology, makes being a patent attorney a particularly rewarding and intellectually stimulating profession.
Physics plays a key role for most processes that are required for the fabrication of advanced nano- and microdevices of all kind.
RSBG AMS is a group of companies offering a wide range of innovative equipment and solutions for demanding nano- and microfabrication and surface analysis processes.
A few examples are shown where physics is applied to push such technologies forward.
In this presentation I will give an overview of my career path through various positions in startups, multi-national corporations, moving to the US and back, and just lately running a management buy-in project and investing my own and other money in a company in Switzerland and running its daily operations.
I will put particular focus on what drove me to leave one position and take on another challenge and will hopefully be able to show that there is a myriad of possibilities outside the laboratory, while still benefitting immensely from the solid education a physicist enjoyed.
Chiral topological semimetals (which possess neither mirror nor inversion symmetries) are a new class of quantum materials that have been predicted to host novel phenomena, such as multifold fermions with large topological charge, long Fermi-arc surface states, unusual magnetotransport and lattice dynamics, unconventional superconductivity, and exotic optical effects, such as a quantized response to circularly polarized light. However, until recently, all experimentally confirmed topological semimetals crystallized in space groups that contain mirror operations, which means that the aforementioned phenomena must vanish.Here, I will present evidence from soft X-ray- and VUV-angle-resolved photoelectron spectroscopy that a family of intermetallic catalysts, including PtAl and PdGa [1,2], are chiral topological semimetals. We directly visualize the multifold fermions in these compounds and show that they carry the largest possible Chern number that can be realized in any metal. We also show experimentally that there is a direct relationship between the handedness of the crystal structure and the electronic chirality (i.e. the Chern number sign) of the multifold fermions. This finding demonstrates that structural chirality can be used as a control parameter to manipulate phenomena that are sensitive to electronic chirality, such as the direction of topological photocurrents. I will then present our latest experimental results about new directions in the field of chiral topological semimetals, including magnetic materials.
[1] N. B. M. Schröter et al., Nat. Phys. 15, 759–765 (2019). [2] N. B. M. Schröter et al., Science 369, 179 (2020).
We present our recent results on the spin texture in chiral topological semimetals, which host multifold fermions, a higher spin-generalization of Weyl-fermions. While ordinary Weyl-fermions display arbitrary spin-textures, multifold fermions are predicted to exhibit spin-momentum locking [1]. We use spin- and angle resolved photoemission spectroscopy to reveal the spin polarization of the Fermi-arcs in PtGa, which has among the largest spin splitting among chiral topological semimetals [2]. Surprisingly, we find a primarily radial spin texture on the Fermi-arcs, which could enable spin-orbit torques different from those predicted for Weyl semimetals.
[1] G. Chang, et al. Nature Mater. 17, 978 (2018)
[2] M. Yao, et al. Nat. Commun. 11, 2033 (2020)
As one of the external stimuli, strain applied to the solids can trigger exotic quantum phenomena such as phase transitions. Strain tuning the band structure and its visualization in ARPES are therefore very attracting and important. Here, we present our recent results on tuning the band structure and visualizing the topological phase transition in a quasi-one-dimension superconductor TaSe3.
I will introduce our recent efforts exploiting some of the varied facets of ARPES. Exploiting synchrotron micro-ARPES we extracted the electronic structure of the spatially competing low-temperature phases in IrTe$_2$. Comparison with theory provides evidence for a molecular-type local bonding mechanism. Using femtosecond time-resolved ARPES at 21 eV photon energy we could extend band mapping into the excited states above the Fermi level, and additionally resolve a detailed reaction pathway during the photo-induced phase transition in In nanowires on Si(111). Simulations constrained by our measurements reveal the ultrafast dynamics of chemical bonds. I will briefly discuss possibilities for combining a micro-focussed XUV source with femtosecond dynamics throughout the Brillouin zone.
The generation of spin current pulses by laser-driven demagnetization links the field of ultrafast magnetism to spintronics. We demonstrate that femtosecond spin injection can be observed by spin and time resolved photoemission experiments.
We study iron films which are excited by a 800 nm pump laser beam. Photoemission by a HHG source in combination with a spin polarimeter is used to measure the spin-split chemical potentials. We observe the spin voltage, the driving force for the spin current.
If we cap our sample with a gold layer, we can study spin injection and accumulation. The thickness dependence of the observed dynamics can be described by a “spin capacitance”.
Electrodes for photocatalytic water splitting have to fulfill several requirements like high light absorption and efficient carrier transport to the surface without energy loss. Cuprous oxide is a prime candidate due to the small, direct bandgap and to abundant and cheap constituents, but the photochemical conversion efficiencies found so far are well below the theoretically possible figures. Using time-resolved ARPES, we studied the (111)-surface of Cu2O and investigated the effects of defects present in the surface. Supported by DFT calculations we could identify oxygen vacancy states to be responsible for carrier trapping and, thereby the low performance of this material.
The observation of neutrinoless double beta ($0\nu\beta\beta$) decay would demonstrate lepton-number violation, imply neutrinos are Majorana particles, and provide information about neutrino masses. LEGEND will search for $0\nu\beta\beta$ with high-purity germanium detectors enriched in $^{76}$Ge operated in an active liquid-argon shield. The first phase will deploy 200 kg of Ge crystals and reach a half-life sensitivity of $\sim 10^{27}$yr. The second phase aims to improve the discovery sensitivity by an order of magnitude with 1000 kg of detectors. By combining the lowest background levels and the best energy resolution in the field, LEGEND will perform a quasi-background-free search for an unambiguous signature at the $0\nu\beta\beta$ decay Q-value of 2039 keV.
A search is presented for heavy neutral lepton (HNL) production in proton-proton collisions using the full CMS Run 2 dataset. The search focuses on final states with three charged leptons - of which two are displaced - and one neutrino, providing a clean signature for long-lived HNL decays. The analysis methods are optimised for HNL decays beyond the CMS tracker system, which extends the sensitivity of previous CMS searches in the high HNL lifetime region. This analysis is also conceived as a basis for future HNL searches in the same phase space region, which will profit from new strategies targeting displaced objects together with the increased luminosity in Run 3.
The search for Heavy Neutral Leptons (HNLs) is performed in inclusive decays of hadrons containing a 𝑏 quark using a mass-lifetime phase space scan. HNLs are weakly coupling particles that can provide a minimal solution to several outstanding problems in particle physics. An inclusive approach is a key point of this analysis which enhances the sensitivity and allows to better constrain HNL parameters. This search employs a frequentist scan of the invariant mass spectrum of the reconstructed HNL candidates. In order to increase the sensitivity for different lifetimes, the search is performed in three regions of HNL displacement.
The introduction of Heavy Neutral Leptons (HNLs) to the Standard Model (SM) would provide a possible explanation to the non-zero, yet small, mass of the SM neutrinos. The search for those particles is also motivated by the fact that, within certain theories, e.g the $\nu$MSM, the HNLs would provide both a dark matter candidate as well as a possible mechanism for baryogenesis. A search for long-lived HNLs produced in B-meson decays, with the CMS experiment at CERN, is presented. The data comes from p-p collisions collected in 2018 using dedicated single muon triggers, corresponding to an integrated luminosity of 41.6 fb$^{-1}$.
SND@LHC is a newly installed detector to study LHC neutrinos in a unexplored pseudorapidity region, using a hybrid system of interleaved emulsion cloud chambers and electronic trackers, followed by a calorimeter/muon system. It allows to distinguish all three neutrino flavours, which are predominantly produced in heavy flavour decays. This is a unique opportunity to probe heavy flavour production at the LHC in a region not accessible to any other experiments and of particular interest for future colliders and for astrophysics. The detector is also able to search for scattering Feebly Interacting Particles.
This talk will review the physics case of SND@LHC and introduce the measurements to be performed in 2022.
The SND@LHC is a neutrino and feebly interacting particles search experiment, based at CERN.
It is located 480 m away from the ATLAS interaction point and consists of a target region built of emulsion-tungsten walls interleaved by scintillating fibre planes, and a hadronic calorimeter-muon identification system, built of scintillating bars and iron absorbers.
All scintillators are read out by silicon photomultipliers and a custom read-out electronics based on the TOFPET2 ASIC, allowing for signal discrimination and amplitude and time measurement.
It has been installed at the end of 2021, ready to take data during Run 3.
The talk will discuss the detector concept, the installation and the commissioning.
ArCLight is a compact dielectric light trap with a large sensitive area, coated with a thin layer of TPB, and read out by Silicon Photo Multipliers (SiPMs). The ArCLights were developed for the ArgonCube $2\times2$ demonstrator detector at University of Bern, with the goal to fulfill the physics requirements for the Dune near detector, namely fast timing and good spacial resolution. These requirements are particularly driven by the demands for an efficient tagging of fast neutrons produced in neutrino interactions in liquid Argon environment.
In this talk the design features, production method, characterization studies and the photon detection efficiency of the ArCLight modules in liquid Argon, are presented.
Excellent particle detection momentum threshold, together with cost-effective scale-up, make the optical TPC, a strong candidate for reducing the systematic errors in future neutrino oscillation experiments. To produce thousands of photons per primary electrons, the TPC is equipped with a gas electron multiplier. These photons, normally in the UV range, are shifted to visible using a PEN wavelength shifter. Following a successful commissioning and data analysis stage, a full report on the first light detection, with photo-multiplier tubes, is given. Simultaneously, an SiPM array was prepared and therefore, the detector is going to enter soon in its second phase, ready for track reconstruction.
I briefly summarize how my education as a theoretical physicist with focus on quantum field theory and critical phenomena has influenced my subsequent work in the alternative investment industry. While developing systematic trading strategies, I stumbled across close analogies between financial markets and second-order phase transitions. This has led to a new model of financial markets as a lattice gas, in which the lattice represents the social network of investors, and the gas molecules represent shares. Combining my physics background with my industry experience in this way is not only a lot of fun, but may also lead to a deeper understanding of financial markets with new risk management applications.
Vacuum instrumentation enjoys an incredibly rich portfolio of applications – from monitoring the roughing pump in sausage packaging plants to controlling pressure in fusion reactors to analyzing gas composition in the most advanced semiconductor processes, spanning about 16 decades of pressure measurement and analysis, within very different environments. We would like to take you on a phyiscists journey to the challenges set by the customers, and to the methods and techniques used to successfully overcome these, some of them 120 years old and still in use others requiring the latest technological insights.
Modern X-ray spectrometers in telescopes employ arrays of transition edge sensors with SQUIDS at cryogenic temperatures. The growing number of sensors requires electrical interconnects with high electrical and low thermal conductivity due to the small cooling power at these mK-temperatures. The same is true for quantum computing applications where additionally HF-losses are important. The author's company Hightec MC AG has been developing such superconducting multilayer flex harnesses on polyimide films to meet these requirements. Along with an introduction of company’s history, we present the manufacturing process of the harness and show that the stress in the Niobium thin films should be tensile to ensure product quality.
We present the development of the biophysical method “focal molography” and discuss the fascinating passage from basic science to a novel bioanalytical concept. The project was propelled by insights that evolved over many years of applied research in the life-science industry. Realization of molography required basic research on a biomolecular system augmented by physics. ETH Zürich provided the ideal environment for the project. The molographic detection principle enables sensitive and reliable label-free optical biosensors. Such sensors are an invaluable tool for bioprocess monitoring and drug discovery. The project lead to the founding of the company lino Biotech AG, the provider of focal molography in the life sciences.
Physics is used at large in both industry and academia. Furthermore, the skills learnt during our university education are broadly applicable. I will present a small subset of these applications through the lens of my personal experience which includes accelerator physics, theoretical and experimental control of superconducting qubits, financial risk management, and quantum computing applications research. I will use this journey to exemplify some available career options and show how some experiences I gained in previous positions were used in a priori unrelated topics. For example, many skills learnt in physics are transposable to finance and I will show how I translated my domain expertise in finance to quantum computing.
The Poster Session is held on Tue and Wed. All posters are to be presented on both days. However, due to technical reasons, the contributions are only listed in the timetable of Tue.
Magnetohydrodynamics (MHD) is a powerful tool to assess the stability of laboratory plasmas. However, kinetic corrections to MHD can be crucial in the weakly collisional environment of a modern tokamak. The ultimate goal of this project is the implementation of a hybrid kinetic-MHD spectral code, which can capture kinetic effects while retaining the advantages and essential structure of the MHD problem. The equations to be numerically solved are presented in the case of a simplified test case. Following the van Kampen approach, the eigenvalue problem is expressed in standard linear form which is more convenient for numerical resolution than the nonlinear equations obtained using the traditional Landau approach.
High-voltage AC power grids are commonly modeled as networks of coupled oscillators. Following a disturbance, the voltage frequencies exhibit coherent wave phenomena. These phenomena are well understood in networks with weakly connected areas. However, these oscillations have also been observed in well-connected large-scale grids. Understanding these phenomena is of great importance as undamped oscillations can lead to blackouts. Using perturbation theory, we show that these oscillations are generic and only weakly sensitive to the connection strength between well-chosen areas. Specifically, we show that the convergence of perturbation theory is mode dependent and that the slowest modes are protected. We connect our theory to Courant’s nodal domain theorem.
The Poster Session is held on Tue and Wed. All posters are to be presented on both days. However, due to technical reasons, the contributions are only listed in the timetable of Tue.
In the context of the EU Horizon project ACDC, we simulate the movement and agglomeration of oil droplets in water under constraints, like confinement, using a simplified stochastic-hydrodynamic model. In the analysis of the network created by the droplets in the agglomeration, we focus both on local and global structures and compare the computational results for various system sizes.
Nanopore-based resistive pulse sensing is an experimental technique that allows characterizing proteins on a single-molecule level. The signal from the nanopore depends on the characteristics of the pore, as well as the shape, volume, and orientation of the protein.
To investigate those current traces, we employed a machine learning algorithm trained on bead-model-based simulation data. Our results revealed that the machine learning approach can extract more information from a single translocation trace compared to the conventional approach (extracting protein shape with an accuracy of 80%). This investigation points toward the most important features of the signal that enables the characterization of a protein in nanopore-based resistive pulse sensing.
The Poster Session is held on Tue and Wed. All posters are to be presented on both days. However, due to technical reasons, the contributions are only listed in the timetable of Tue.
We use far-infrared ellipsometry to determine the anisotropic optical response of the TbMnO3 film in the spectral range of 100-700 cm-1 and temperature range of 10-300 K. The 44 nm thick sample was grown by Pulsed Laser Deposition on an orthorhombic YAlO3 (010) substrate.
We were able to extract phonons properties, and observe softening due to the multiferroic phase transition. The analysis of the TbMnO3 thin film is complicated by the anisotropic response of the YAlO3 substrate, which we have precisely determined a priori on a series of YAlO3 crystals with various surface cuts.
We will present a new magneto-ellipsometric instrument built at the Physics Department, University of Fribourg. It is based on combination of time-domain terahertz and Fourier-transform infrared spectrometers, equipped with He-flow cryostat and split-coil 7 Tesla magnet.
Apart from standard transmission geometry, the instrument is designed for reflection ellipsometry measurements at angles of incidence 75° and 80°, with field parallel or perpendicular to the sample surface. The operation can be switched between the THz and IR branch in-situ, and both beam paths are in vacuum.
With this instrument, we aim at studies of magneto-optical response of strain engineered thin/ultrathin films of strongly correlated oxides.
We report the pulsed laser deposition (PLD) of multilayers of the cuprate high-$\mathrm{T_C}$ superconductor $\mathrm{YBa_2Cu_3O_{7-\delta}}$ (YBCO) and the iridate $\mathrm{Sr_2IrO_4}$ (SIO) which exhibits a strong spin-orbit-coupling (SOC). The magneto-transport characteristics of the heterostructures are investigated.They reveal a strong and comparatively long-ranged proximity effect. This gives rise to a suppression of the superconducting response of the YBCO layers up to a thickness of about 14 nm.
Moreover, we find a strong and unusual magnetic field dependence.
These results point towards a complex interplay between the strong SOC in SIO and superconductivity in YBCO and call for further studies of the microscopic electronic and magnetic properties of these layers.
Resonant ultrasound (RUS) probes the resonant frequencies of a solid to determine the complete elastic tensor. RUS is sensitive to detect both the symmetry variation and coupling of other degrees of freedoms to the lattice. Notably, novel electronic ground states may be detected due to their symmetry breaking order parameters resulting in a change of resonant frequencies. Similarly, the coupling of the lattice to spin or charge degrees of freedom may be uncovered by changes in the sound wave attenuation or velocity. Here we will present our development of a resonant ultrasound setup for measurements at low temperature and at magnetic fields optimized to study of quantum matter.
In quantum magnets, simple degrees of freedom with short-range interactions lead to a plethora of emergent many-body phases with different exotic properties. Uniaxial pressure allows tuning these interactions selectively and engineer the underlying Hamiltonians. Hence, the properties of the emergent phases can be controlled on-demand.
One system where such selective tuning is very pertinent is a quantum spin ladder, where only two exchange constants are relevant. In this contribution, we will present our developments of integrating a uniaxial strain device into a Nuclear Magnetic Resonance (NMR) apparatus as well as preliminary measurements on a model ladder system.
For the doped samples with a nominal compositions of K3-p-terphenyl, we observed a pronounced enhancement of some low-energy phonon modes that is in fair agreement with the prediction of lattice dynamical calculations. Moreover. We observed electronic excitations that give rise to a pronounced polaronic band and a weak Drude-like peak at the origin that is due to free carries with a plasma frequency. No anomalous changes of the Drude-response have been observed in the low temperature regime that could be taken as evidence of a bulk-like superconducting transition. An inhomogeneous SC state with a very small volume fraction
Layered transition metal dichalcogenides are an example of the van der Waals (vdW) materials, hosting many interesting states of matter like charge density wave ordering and superconductivity. In many vdW systems, the material properties can be profoundly and surprisingly sensitive to seemingly minor changes in composition or structure. Currently we are investigating vanadium intercalated V$_x$TaS$_2$. Despite the very dilute concentration of vanadium ($x\leq$ 0.05), our preliminary results show significant changes in the Fermi surface topology and band composition compared to the parent 2H-TaS$_2$. The discovered spectral features indicate the substantial influence of new c-axis ordering and inter-layer interactions on the electronic properties of the system.
A technique to unlock spatial resolutions in the order of 10$\,$nm is soft x-ray ptychography. Ptychography consists of moving the sample through a beam of monochromatic x-rays, all the while collecting diffraction patterns from the overlapping illumination spots. Recovery of the complex transmission function is achieved with a reconstruction algorithm. Measurements in the soft x-ray regime benefit from strong x-ray magnetic circular dichroism (XMCD) and x-ray magnetic linear dichroism (XMLD) contrasts. These serve to analyse ferromagnetic and antiferromagnetic materials, respectively. We present the development of the new soft x-ray ptychography endstation at the Swiss Light Source. First results include the imaging of the spin cycloid in multiferroic bismuth ferrite.
Superconducting circuits and spins confined in semiconductor structures represent two leading qubit implementations. Continuous fabrication improvements and a better understanding of semiconductor-oxide interfaces are crucial to enhancing qubit performance.
We use noise spectroscopy in silicon quantum dots to evaluate the substrates and oxides. Furthermore, we present a novel design for superconducting resonators, aiming to improve their internal quality factor by modifying the conductor geometry and minimizing the presence of oxides at the relevant interfaces. We study the reproducibility of the fabrication and explore the properties of different superconducting materials. Addressing these sources of noise and reducing their impact on qubits will be critical for future development of scalable quantum-computing platforms.
By means of the ultrafast electronic diffraction (UED) in reflection geometry, we observe argon atoms adsorbed of graphite with atomic resolution. The diffraction patterns of solid argon adsorbed on graphite compared with simulation shows FCC structure in (111) orientation.
Interesting physical phenomena emerge from the experiment as the phase diagram dependence on substrate surface ; the compression of the lattice during lattice growth and warm up ; the ordering of lattice surface before sublimation point during warm up.
This experiment drives us to study the fundamental science of 2D materials.
ZrSe2 in its pristine bulk form is an insulator and does not support a CDW phase. However, a recent study of mono- and few-layer ZrSe2 on graphene reports the observation of a 2x2 CDW driven by charge transfer from the substrate.[1]
We use cryogenic STM and STS to study in-situ cleaved bulk ZrSe2 and present a spatial spectroscopic investigation of native defects and their influence on the electronic structure of ZrSe2. Our study finds spatial modulations in the LDOS consistent with the previously reported results, suggesting that a similar CDW phase in bulk ZrSe2 may be driven by native atomic defects.
[1]Ren et al., Nano Letters 22 476-484 (2022)
Silicon FinFETs are used in classical CMOS electronics but can also provide an attractive platform for the implementation of spin qubits. Classical transistors usually have highly doped contacts that determine device polarity (n-type or p-type). Our FinFET quantum dots have Schottky contacts formed by a silicide. These contacts can be ambipolar for a midgap silicide such as e.g. NiSi. For a low contact resistance to holes, PtSi is more suitable because it has a lower Schottky barrier height. Here, we study the behavior of these Schottky contacts at cryogenic temperatures and with intrinsic silicon substrates and also investigate ErSi as an potential low resistance n-type Schottky contact material.
Exotic states of matter are predicted to be found in 2D bilayer systems such as InAs/GaSb heterostructures. These are usually described as two adjacent quantum wells of InAs and GaSb where the conduction band of the former lies below the valence band of the latter. We present a variation of this structure using an insulating AlSb barrier between InAs and GaSb layers, acting as an n and a p layer, respectively. We highlight the observation of a two-dimensional electron gas (2DEG) and a two-dimensional hole gas (2DHG) created in the vicinity of the insulating AlSb barrier. Using capacitance techniques, we succeed to measure the accumulation of charge carriers close to the barrier already in equilibrium regime, i.e., without any applied DC voltages. By applying positive DC bias, we modify the density of the 2D charge gas as can be seen via the Shubnikov-deHaas (SdH) oscillations. This scenario is motivating for deeper understanding about how excitons are generated and behave in an Excitonic condensate or Bose-Einstein condensate (BCS) regime. Further interaction effects that are created from this observation will be discussed.
The Poster Session is held on Tue and Wed. All posters are to be presented on both days. However, due to technical reasons, the contributions are only listed in the timetable of Tue.
Developing and understanding novel quantum materials pushes angle-resolved photoemission (ARPES) into new frontiers of resolution and extreme conditions. ULTRA endstation at the SIS beamline of the Swiss Light Source is a novel system for high-resolution ARPES at temperatures down to 4 K. With independent 6-axis control, minimal thermal drift, deflector scanning, and easy alignment, ULTRA is not only powerful, but also user-friendly and geared toward high-throughput spectroscopy. A newly added instrument cluster for in situ film growth and scanning probe techniques enables cutting-edge investigations of oxide films and heterostructures. I will summarize the present status of ULTRA, highlight recent science, and discuss future plans, including integration into SLS 2.0.
Soft-X-ray ARPES in photon-energy range around 1 keV combines electron-momentum resolution with large photoelectron escape depth, allowing studies of buried heterostructures and impurities. For example, experiments on AlGaN/GaN find anisotropy of the interfacial states, propagating to electron transport [Nature Comm. 9 (2018) 2653]. For LaAlO3/SrTiO3, resonant photoexcitation of Ti-derived interfacial charge carriers resolves their multiphonon polaronic nature [Nature Comm. 7 (2016) 10386]. The NbN/GaN heterostructures show the NbN-derived Fermi states well separated from GaN in energy and momentum, protecting superconductivity [Sci. Adv. 7 (2021) eabi5833]. Resonant photoexcitation of the magnetic Fe impurity states in In(Fe)As identifies their integration into InAs, allowing high electron mobility [Phys. Rev. B 103 (2021) 115111].
The electron spin is the crucial parameter of modern spintronics and therefore its determination in energy structures of solids is highly important. In order to boost spin-resolved ARPES' efficiency and accessibility, a prototype of a new imaging-type multichannel spin detector for electrons based on Mott scattering is being developed. We present the current status of the project, focusing on the issues of signal acquisition and processing. Two possible operation regimes, namely, «accumulating» and «single-electron counting» modes are compared in conjunction to intensity and signal-to-noise ratio requirements, which determine reliable detection of spin asymmetry. Further development directions are outlined.
Electron-boson interaction is quantified through the Eliashberg function $\alpha^2F(\omega,\mathbf{k})$, accessible through the electron self-energy $\Sigma(\varepsilon,\mathbf{k})$. In ARPES, $\Sigma(\varepsilon,\mathbf{k})$ is readily extracted from the spectral function, requiring little more than a parametric expression for the quasiparticle dispersion $\xi(\mathbf{k})$ in order to discern the photoemission kink resulting from $\Sigma(\varepsilon,\mathbf{k})$. However, $\alpha^2F(\omega,\mathbf{k})$ is highly sensitive to the parameters of $\xi(\mathbf{k})$, which itself can be difficult to determine in the presence of strong electron-boson interaction. We will describe a self-consistent and simultaneous Bayesian optimisation method for $\Sigma(\varepsilon,\mathbf{k})$ and $\xi(\mathbf{k})$, yielding the most probable $\alpha^2F(\omega,\mathbf{k})$ in an automated fashion. This optimisation allows us to discern between bosonic contributions and orbital hybridisation in ARPES spectral functions.
Probing the electronic properties of two-dimensional (2D) dopant layers ($\delta$-layers) in silicon is crucial to establish the quasi-2D characteristics of functional quantum-electronic devices. Here, we present the first soft x-ray angle-resolved photoemission spectroscopy (SX-ARPES) measurements of silicon $\delta$-layers. The SX regime allows us to directly probe through the native surface oxide, where we demonstrate nearly ideal 2D electron states exist in these technological silicon samples. We quantify the morphology of the $\delta$-layer conduction valleys and deconvolve the spatial confinement of the $\delta$-layer directly from the SX-ARPES $k_z$-response. We use this to demonstrate that arsenic $\delta$-layers yield the thinnest (< 1 nm) 2D electron liquids ever fabricated in silicon.
The Poster Session is held on Tue and Wed. All posters are to be presented on both days. However, due to technical reasons, the contributions are only listed in the timetable of Tue.
With an established model[1,2], we determine the attosecond photoemission time delay in the charge density wave material CuTe, by means of spin- and angle-resolved photoemission spectroscopy. While accessing absolute time delay information by measuring spin polarization as a function of binding energy, with its moderate correlation strength, this result constitutes a part of the study on the connection between correlation strength and time delay, along with SARPES measurements done on noncorrelated Cu and strongly correlated BSCCO.
Furthermore, we present a pump-probe ARPES experiment which visualizes the coherent phonon oscillation which is characteristic of a CDW state.
We present preliminary data measured in the multiferroic Y-type hexaferrite Ba1.3Sr0.7CoZnFe11AlO22 representing the time-resolved response of the crystal structure after short and intense THz excitation of an electromagnon. Electromagnons are emergent collective excitations that consist of optical phonons strongly coupled to magnons. It is believed that an electromagnon can alter the magnetic structure in multiferroics and thereby affect or switch the electric polarization. Employing time-resolved THz-pump x-ray diffraction carried out at the Bernina endstation (SwissFel, PSI), we characterized, for the first time, the structural dynamics accompanying the electronmagnon. Detailed interpretation of the acquired data may further hint at the alteration of the magnetic structure and hence polarization switching.
The Poster Session is held on Tue and Wed. All posters are to be presented on both days. However, due to technical reasons, the contributions are only listed in the timetable of Tue.
Quantum spin-liquids (QSLs) are novel phases of quantum matter defined by a highly-fluctuating and massively entangled ground state as T -> 0 K. A candidate QSL material is YbBr3, an effective spin-1/2 2D honeycomb system.
Inelastic neutron scattering experiments on this material reveal a broad continuum of scattering associated with strong quantum fluctuations of the magnetic system, which suggests that YbBr3 is only short-range correlated down to at least T = 100 mK.
Our recent investigations of the magnetic correlations of YbBr3 at CAMEA and TASP at PSI, aim to quantitatively describe the dynamical spin correlations in the material under the application of an external magnetic field.
Ce3TiSb5 belongs to the class of frustrated Kondo-lattice systems. We have carried out detailed magnetization and specific heat measurements that reveal a complex magnetic phase diagram. We also report our results from recent single crystal neutron diffraction to investigate the magnetic order. Most notably, we found reentrant magnetic order as a function of magnetic field.
Many neutron scattering experiments rely on single crystal mosaics, to optimize the overall scattering mass volume. Such alignment of mosaics is typically done through tedious and time-consuming manual labour. Here we present a semiautomated protocol for alignment of quasi-two-dimensional materials.
Kagome ice is a two dimensional critical state of algebraic spin correlations formed by applying a moderate magnetic field along the [111] direction of a pyrochlore spin ice. Field tilts away from perfect alignment tune the algebraic correlations, leading to symmetry-sustaining Kasteleyn transitions. We present a detailed experimental/theoretical study of the kagome ice Coulomb phase, exploring the tuning of critical correlations by applied field, temperature and crystal orientation. We observe the continuous modification of algebraic correlations with polarized neutron scattering experiments, which are described by numerical simulations of an idealized model. Kagome ice is a remarkable example of a critical/topological state in a real system subject to the experimental control.
I will present our current understanding of the magnetic degrees of freedom in Ni3TeO6, a non-centrosymmetric hexagonal material that undergoes a field-induced first-order phase transition with emergent multiferroic properties. Using neutron scattering under in-plane magnetic fields we find that the collinear spin structure becomes likely chiral at large fields. The low-energy spin-wave excitations at zero field act as a precursor of the putative chiral state. They split in field and provide evidence for a Zeeman-induced mode condensation at the magnetic phase boundary.
A correlated liquid state was reported in the cerium stannate pyrochlore Ce2Sn2O7 at temperatures below 1 Kelvin. Its nature remained elusive, but with additional knowledge on the crystal-electric field scheme of cerium, the case was further investigated based on degrees of freedom having both magnetic dipole and magnetic octupole components. These works agree towards a quantum spin ice (QSI) based on a manifold of ice-rule correlated octupoles – a state that was conceptualised by earlier theoretical works. We review the findings reported so far on cerium pyrochlores and present new experimental results that further hint at these materials being representatives of a QSI – the model 3D quantum spin liquid.
The Poster Session is held on Tue and Wed. All posters are to be presented on both days. However, due to technical reasons, the contributions are only listed in the timetable of Tue.
The LEMING experiment aims to test the equivalence principle for second-generation matter, using a cold muonium beam (bound $\mu^+ e^-$), where the inertial mass is dominated by the muon.
The feasibility of such a measurement relies on measuring the gravitational deflection of a lifetime-limited atomic beam. In this poster, the feasibility of an atomic interferometer is discussed, which could potentially provide a percent-level measurement of g of muonium.
SU(2) gauge theory with $N_f=24$ massless fermions is non-interacting at long distances, i.e. it has an infrared fixed point at vanishing coupling. With massive fermions the fermions are expected to decouple at energy scales below the fermion mass, and the infrared behavior is that of confining SU(2) pure gauge theory. We demonstrate this behavior non-perturbatively with lattice Monte Carlo simulations by measuring the gradient flow running coupling.
A small, 18-cm bending radius double-focalizing spectrometer has been in use for the investigation of beta spectra from radioactive sources since its construction around 1995, equipped with a small solid-state detector and a state-of-the-art readout. Extensive datasets have been collected to calibrate the device and understand its behaviour, to be leveraged in the measurement of beta spectra that are poorly understood and/or never measured to date. An overview will be given of the device and its performance, and the ongoing measurements.
Physics education has in the past often been centred either on technological applications or the very large or small scales of the universe. As a middle ground, everyday phenomena, biological or soft matter systems are however also very useful to particularly stimulate students without an innate interest in Physics. In this presentation I will show how simple experiments on everyday phenomena can excite children for the subject of Physics. In addition, I will show how a standard Physics curriculum can be adjusted to cover the same topics with an emphasis on living matter and biological phenomena. This is not only useful for introductory lectures for life science students, but can also be used in high schools in order to increase the level of interest of the students by connecting the subject to their world.
Considering its geographical size, Switzerland hosts a relatively big number of large-size scientific research infrastructures. With respect to size and esteem, the number one on the list is, of course, CERN, the internationally funded institution situated in Geneva with France as the other host country. Its impact on the prestige of the scientific landscape of Switzerland is enormous. This contribution is intended to show how a relatively large number of national large-scale research infrastructures in Switzerland was established and examples of achievements will be presented. Apart from offering first-rate research opportunities for Swiss-based scientists, some of them play an important role at the international level as user institutions with open access to researchers also from abroad. Often the construction of these infrastructures and their upgrading is based on implementing innovative ideas with the help of demanding engineering work and craftsmanship, also with benefits to Swiss-based industries.
Natural language processing models in organic chemistry have emerged as one of the most effective, scalable approaches for capturing human knowledge and modelling chemical processes. Its use in machine learning tasks demonstrated high quality and ease of use in problems such as predicting chemical reactions [1-2], retrosynthetic routes [3], digitizing chemical literature [4], predicting detailed experimental procedures [5], designing new fingerprints [6] and yield predictions [7]. In this talk, I'll talk about the impact of language models in chemistry by highlighting the critical role of NLP architectures in implementing the first cloud-based AI-driven autonomous laboratory [8].
Finally, I will discuss recent applications of language models to the characterization of unknown enzymes, the recovery of 3D features from 1D sequences, the development of human-in-the-loop schemes for retrosynthetic strategies, and the promotion of sustainability and green chemistry strategies using ad-hoc AI models.
In recent years the simulation of molecular systems with digital quantum computers has amassed a great deal of attention as the community realized quantum chemistry represents one of the most promising and impactful applications of quantum computing. This work has focused on the design of quantum algorithms for the resolution of electronic and vibrational structure problems as well as the simulation of molecular quantum dynamics.
The fundamental nature of dark or invisible matter remains one of the great mysteries of our time. A leading hypothesis is that dark matter is made of new elementary particles, with proposed masses and interaction cross sections spanning an enormous range. Amongst the technologies developed to search for dark matter particles, two-phase (liquid and gas) xenon time projection chambers are currently leading the field, providing unprecedented sensitivities and a large discovery potential. I will present the development of these detectors from their earliest stages, with focus on the XENON programme. I will show results from XENON1T, the status of XENONnT which is currently taking data deep underground, and discuss the ongoing the R&D towards the next-generation DARWIN experiment.
The Poster Session is held on Tue and Wed. All posters are to be presented on both days. However, due to technical reasons, the contributions are only listed in the timetable of Tue.
Additive manufacturing approaches were recently exploited for the fabrication of exquisite photonic objects, but the angle-dependence observed limits a broader application of structural color in synthetic systems. Here, we propose a manufacturing platform for the 3D printing of complex-shaped objects that display isotropic structural color generated from photonic colloidal glasses. We print structurally colored objects from aqueous colloidal inks containing monodisperse silica particles, carbon black, and a gel-forming copolymer. Using Rheology and Small-Angle-X-Ray-Scattering measurements we identify the processing conditions leading to printed objects with tunable structural colors. Multimaterial printing is eventually used to create complex-shaped objects with multiple structural colors using silica and carbon as abundant and sustainable building blocks.
Strongly correlated heterogeneous dielectrics can exhibit structural coloring. Such materials are widely used by nature. Thus, it is desirable to derive a bioinspired design platform for bright ultra-stable synthetic pigments. This can be achieved by using spherical aggregates of nanoparticles, known as photonic balls (PB).
In our research, we experimentally study the light scattering of PBs and developed a theoretical framework to explain a structural color formation by them. We use photonic balls as a model system to elucidate fundamental aspects of phase delay and momentum transfer of light in optically soft heterogeneous dielectric materials. We use the developed knowledge to demonstrate the PB's potential for graphical printing applications.
In the context of Industry 4.0, the inkjet printing technology has the unrivaled advantage of being digital and extremely versatile by its nature. This technology offers a new universe of highly customizable products, adding multi material and while at the same time being fast, flexibly scalable and cost-effective.
The recent breakthrough in the understanding of structurally colored materials found in nature provides new design platforms for colored materials and pigments in a variety of applications such as packaging, coatings, electronic paper and sensor applications.
The aim of this project is to design inks that generate colors via interference by structural pigments and that can be printed with state-of-the-art inkjet technology.
Photonic nanostructures can vary in their degree of order and their optical appearance is often altered by pigmentary content. Longhorn beetles display vivid colours in the UV-VIS spectral range and rely on varying degrees of (dis)order combined with pigments to create complex colour patterns. The green-orange coloured subspecies Sternotomis amabilis ssp. sylvia was studied by combining optical characterization and ultrastructural analysis of the coloured scales that adorn the insects’ bodies. Body-centred cubic and amorphous photonic crystals inside scales featuring micrometre-scale cortex ribs produce angle-independent blue-green and orange colour, respectively. Additionally, these photonic structures contain pigments, thus illustrating the complex interplay of structural and pigmentary colour in longhorn beetles.
The interplay between disorder and order in structured materials has been increasingly recognized as an important parameter for the creation of a wide range of optical effects from iridescent bright colors created by ordered (crystalline) structures, angle-independent matt colors found in disordered (correlated) structures to extreme white appearances stemming from anisotropic (random) network systems.
We combine analytical modeling and in silico synthesis of 3D structures for FDTD optical simulations to study the limitations of structural color in natural and synthetic materials. The predictive nature of such models allowed for strategies towards an improved optical response to be proposed in silico and subsequently applied in self-assembled polymeric systems.
Inspired by nature, structural colours can be mimicked by self-assembling monodisperse colloids into crystals. The amount of order in the crystalline structure impacts the iridescence (ordered) and non-iridescence (slightly disordered) of the colours.
This project is looking at introducing disorder into the system through non-spherical dimpled particle templates. The dimples introduce an inherent type of disorder into the system, the idea being that the disorder can be controlled by the dimple size.
The dimpling process changes the particle's surface properties, thereby changing the stability and the self-assembly at the liquid interface. Particle synthesis and surface preparation has to be optimised to enable the formation of semi-ordered crystalline arrangements.
Recent experiments with metallic nanowire devices suggest that superconductivity can be suppressed by the application of electric fields, at odds with current understanding of electrostatic screening in metals. We demonstrate that the control of superconductivity in such switches does not depend on the presence of an electric field at the nanowire surface but requires a current of high-energy electrons (below 100 fA in our devices). The suppression of superconductivity is most efficient when electrons are injected into the nanowire, but similar results are obtained when a current flows between two remote electrodes without electrons reaching the nanowire. In the latter case, high-energy electrons decay into out-of-equilibrium phonons which propagate through the substrate and affect superconductivity in the nanowire by generating quasiparticles.
The kagome lattice, the most prominent structural motif in quantum physics, benefits from inherent nontrivial geometry to host diverse quantum phases. We utilized muon-spin relaxation to probe charge order and superconductivity in kagome superconductors (K,Rb)V$_{3}$Sb$_{5}$ [1]. We observe a striking enhancement of the internal field width sensed by the muon ensemble, which takes place just below the charge ordering temperature. We further show a multigap and nodal [2] superconductivity in (K,Rb)V$_{3}$Sb$_{5}$. Our results point to time-reversal symmetry-breaking charge order intertwining with unconventional superconductivity in the correlated kagome lattice, offering unique insights into the pairing mechanism.
[1] C. Mielke III et.al., and Z.Guguchia, Nature 602, 245-250(2022).
[2] Z. Guguchia et.al., arXiv:2202.07713v1(2022).
High-temperature superconducting cuprates are an excellent model system to study the relationship between intertwined quantum phases. We aimed to influence the competition between superconductivity and charge order in La2-xSrxCuO4 (LSCO) by applying strain along the tetragonal c-axis direction, tuning the next-nearest neighbour hopping strength. X-ray diffraction measurements were performed at DESY to track charge order at different temperatures, dopings, and magnetic fields. Our results suggest, that c-axis strain drives the system closer to the state achieved with magnetic field. So, it stabilizes the charge ordered state while superconductivity is weakened, providing a fruitful approach to study the interplay between the two phenomena in the cuprates.
We compare the infrared responses of the underdoped cuprate superconductor YBa2Cu3O6.6 and the so-called telephone-number-compound Sr2Ca12Cu24O41. The charge carriers of the latter reside in layers of weakly coupled two-leg ladders.
The response of YBa2Cu3O6.6 was previously shown to exhibit a characteristic pseudogap and precursor superconducting pairing that develop well above Tc [1]. The infrared spectra of Sr2Ca12Cu24O41 reveal surprisingly similar features. A pseudogap appears here along the rungs and signatures of pair formation are seen along the legs of the ladders. This analogy provides evidence in favor of a stripe-like electronic structure of YBa2Cu3O6.6 and other high-Tc cuprates.
[1] A. Dubroka et al., Phys. Rev. Lett. 106, 047006 (2011).
Superconductivity with a critical temperature $T_C$ $\sim$ 5.25 K was recently reported in the Cr-based superconductor Pr$_3$Cr$_{10-x}$N$_{11}$. The large upper critical field $H_{C2}$ $\sim$ 20 T, and the strong correlation between 3$d$ electrons derived from specific heat, suggest the unconventional superconductivity nature of this compound. We performed muon-spin rotation/relaxation ($\mu$SR) measurements on a high-quality polycrystalline of Pr$_3$Cr$_{10-x}$N$_{11}$ down to 0.027 K, and specific heat measurements under different magnetic fields up to 9 Tesla. Our $\mu$SR data indicate that time-reversal symmetry is broken in the superconducting state of Pr$_3$Cr$_{10-x}$N$_{11}$, and the superconducting energy gap is consistent with a $p$-wave model, which is also supported by the specific heat data.
Experimentally simple cubic phosphorus displays a peculiar pressure-$T_c$ curve with valley- and ridge-like features between 12 and 50 GPa. From the theoretical side, a simple electron-phonon mechanism proves insufficient to describe this behaviour. To address possible effects coming from electronic correlations and plasmonic contributions we have solved the parameter free gap equation of density functional theory for superconductors. We find that an electron-electron interaction kernel obtained from a one-shot $GW$ calculation predicts values of $T_c$ in the correct range. Additionally including a correction of the band structure from the quasi-particle energies significantly improves $T_c$ in the high-pressure region.
Kagome materials have attracted much interest recently as they may host topological bands, flat bands, superconductivity, unconventional magnetic properties, etc. In this talk, we present our work on one example of magnetic Weyl kagome material called Fe3Sn2 by using laser micro-ARPES. With a small spatial resolution of a few microns of the laser, we show that the breathing kagome pattern in Fe3Sn2 manifests itself in twin domains that are otherwise un-resolved in conventional synchrotron-based ARPES experiments. From these untangled twinned areas, we analyzed the electron pockets at the zone center and discover the band characteristic follows the marginal Fermi liquid hypothesis indicating a break from a Fermi liquid picture.
Charge-density waves (CDWs) represent a model system for broken-symmetry states arising from the strong interplay of the charge and lattice degrees of freedom. Manipulation of such collective states promises microscopic insight into the fundamental interactions underlying the transition, and novel opportunities for applications. Time- and angle-resolved photoemission spectroscopy (trARPES) as well as ultrafast diffraction probes nowadays yield an unprecedented view on the intricate dynamics in such systems. I will discuss recent examples of photoinduced phase transitions in CDW systems, including nonthermal CDW order at electronic temperatures far above the equilibrium transition temperature, and a transient modification of quasiparticle scattering rates due to the influence of the CDW energy gap.
The material 1T-IrTe2 is a transition-metal dichalcogenide with a substantial coupling across the planes. Upon cooling, it undergoes a first-order phase transition at about 278 K from a 1 × 1 × 1 phase into a 5 × 1 × 5 phase. Here, we present a time-resolved x-ray photoemission spectroscopy (tr-XPS) and a time-resolved angle resolved photoemission spectroscopy (tr-ARPES) studies using the FLASH free electron laser combined with an optical laser. We reveal the dynamics of the first phase transition and highlight that there exists a threshold fluence above which a partial phase transition takes place. In parallel, we perform a tr-ARPES study, which allows us to support our deductions.
Due to its topological properties, skyrmions offer appealing interest in both fundamental and in spintronic applications. Here, we show combining a femtosecond laser and real space imaging technique in a cryo-Lorentz Transmission Electron Microscope that we can rotate the skyrmion lattice by a discrete amount in a coherent and fully deterministic manner. Using circular polarized pulses in a double-pump experiment and micromagnetic simulation, we demonstrate that we drive via inverse faraday effect a collective magnetic mode, named breathing mode. This excitation provides the required torque to rotate the lattice at a speed nine orders of magnitude faster than previously reported. This new mechanism opens the path towards novel ultra-efficient devices.
Local excitations in magnetic materials are usually highly incoherent, since they dephase quickly due to mutual interactions. However, there are interesting exceptions to this common lore.
Our study of the random rare-earth magnet LiY$_{1−x}$Tb$_x$F$_4$ reveals that a combination of hyperfine interactions, external magnetic fields and disorder allows certain excitations on pairs of Tb sites to retain coherence for remarkably long times, as dominant decoherence channels are suppressed. The remaining decoherence then probes the slow dynamics in the neighborhood of these degrees of freedom, which thus act as quantum sensors. This is particularly interesting as a means to probe the nearly many-body localized dynamics of strongly disordered dipolar magnets.
We report how a new type of chiral superconducting phase can be stabilized in photodoped frustrated Mott insulators. The metastable phase features a spatially varying order parameter with a 120 degree phase twist which breaks both time-reversal and inversion symmetry. Under an external electric pulse, the 120 degree chiral superconducting state can exhibit a second-order supercurrent perpendicular to the field in addition to a first-order parallel response, similar to a nonlinear anomalous Hall effect. This phase can be tuned by artificial gauge fields when the system is dressed by high-frequency periodic driving. The mechanism revealed in this study can be realized in both cold-atom quantum simulators and correlated solids.
Systems with spin orbit coupling (SOC) driven out of equilibrium give rise to interesting electron dynamics due to their coupling between the electron spin and momentum. Recent efforts have been made in order to understand the imprints of SOC on the high harmonic generation spectra of solids. In a parallel development, the field of non-equilibrium superconductivity in unconventional superconductors has lately attracted a lot of attention due to the prospect of Higgs-spectroscopy. We extend these studies by looking at the interplay of the spin related observables and collective excitations. Emphasis will be put on their non-linear signatures and thus relating the results to the already established normal state non-equilibrium dynamics.
The study of CP violation and mixing in charm meson decays is a probe of possible interactions beyond the Standard Model, and is complementary to the Beauty sector. The LHCb experiment, at CERN, has collected copious data samples of billions of charm hadron decays from 2011 to 2018, allowing to study CP violation and mixing in D0 meson decays at extremely high precision.
This talk will present the experimental challenges of the measurement of the charm-mixing parameter yCP at LHCb. The final measurement is seen to improve its current world average by a factor of four.
Supersymmetry (SUSY) is an extension of the Standard Model (SM) of particle physics that aims to fill gaps in SM by predicting a SUSY partner for each SM particle. I am performing a SUSY search dedicated to analysing full LHC ATLAS Run2 data for 3rd generation squarks with top and bottom quarks and missing tranverse energy for the undetectable SUSY particles called neutralinos (tbMET) as final states. This analysis focusing on tbMET final state is interesting as it is optimised with a branching ratio of 50% which makes this more dominant compared to searches with ttMET/bbMET final states. In this talk I will present the ongoing work on this analysis.
Despite its many successes, the Standard Model leaves some fundamental questions
unanswered, such as the hierarchy problem or dark matter. An elegant solution is offered by supersymmetry, which extends the Standard Model by introducing new particles and their interactions. This talk introduces the concept of R-parity violating supersymmetry and describes the search for R-parity violating supersymmetry in an all-hadronic multi-jet final state using the full Run-2 dataset from the ATLAS detector. Challenges arising from the combinatorial problem of the final state and from the signal-like background in proton-proton collisions are discussed, and solutions derived by the analysis team are presented.
Experiments at the LHC face exceptional challenges to acquire data, with the trigger system being from the most strained ones. The ATLAS trigger employs software-based selections at a second stage, referred to as the High-Level-Trigger. Selections on jets originating from b-quarks (b-jets) figure among the most CPU intensive ones, due to the necessity of running track reconstruction algorithms. To allow low transverse energy thresholds in selections with b-jets, a special neural network was employed to provide an early filter before executing precision tracking. The network uses coarser quality tracks, and no primary vertex reconstruction. This approach leads to significantly reduced rates while maintaining high b-jet tagging efficiencies.
This analysis presents a measurement of the CP structure of the Yukawa coupling between the H and top quarks at tree level. We studied a data sample with several final state leptons, enriched in ttH and tH production, collected by the CMS experiment at the CERN LHC in proton-proton collisions at $\sqrt{s}=13TeV$, corresponding to an integrated luminosity of $137fb^{-1}$.
To separate the signature of a pure CP-even H interaction from a pure CP-odd one, we use machine learning techniques. Fractionary CP-odd contributions are not observed and hence in agreement with the SM predictions of a CP-even H. Determining $|f^{Htt}_{CP}|=0.59$ with an interval of (0.24,0.81) at 68% confidence level.
After the end of the CERN Long Shutdown 2 (LS2), the NA64$e$ experiment has resumed its search for dark sectors through its complementary experiment NA64$\mu$ at the CERN SPS M2 beamline, looking for light dark bosons weakly coupled to muons. In addition to enlarging the sensitivity of the NA64$e$ probed parameter space motivated by thermal relic dark matter, it also aims at bringing possible explanation to the recently confirmed $(g-2)_\mu$ anomaly. In this talk, the first test run results of the NA64$\mu$ experiment are discussed, alongside with its future prospects at the LS3 horizon.
In this talk we will discuss photonic materials from various points of view, taking nature as source of inspiration. We will go into the relation between the physical structure of a material and its resulting optical properties and we will look at ways to influence the structure of a material using the light itself thereby creating a two way interaction: the structure determining the optical properties and the light influencing the structure. The application of photonic materials in micro robotics will also be looked into, in particular how one can realize a “photonic hand” that automatically grabs particles of certain colour and microscopic robots that can walk, using light as source of energy.
The scales of the Cyphochilus beetle exhibit one of the whitest whites observed for organic materials up to date. The intense and broadband reflectance is striking as the scales are composed of a very thin (7-8$\mu$m) disordered network made of low refractive index chitin rods (n$\sim$1.55). We will first present the speckle frequency correlation setup used to characterize these samples. We will then show how they can be used as bio-templates for the design of optimized high index diffuse reflectors. Our findings suggest that bio-inspired photonic material design can prove to become instrumental for the development of ultra-thin diffuse reflection coatings with thicknesses comparable to the wavelength of light.
Nanostructured dielectric materials with a photonic bandgap (PBG) are considered “semiconductors for light” and promise rich fundamental physics and multiple technological applications, such as low-loss waveguides, perfect reflectors, or optical elements for computers. In PBG materials, the propagation of electromagnetic waves is forbidden within a specific frequency range. Recently, dielectric 2D foam networks, potentially produced on a large scale using self-assembly, have been numerically predicted to have a large PBG. To check the potential of 3D foam-like dielectric networks, we report, for the first time, the 3D printing by 3D laser Nanolitography and experimental PBG study of foam-like photonic crystals.
The beetle Euprotaetia.nox possesses a black, velvet like allure. Through optical microscopy and spectroscopy, it is found that the cuticle of this insect demonstrates far greater optical absorption than common insect cuticle. Electron-microscope investigations reveal the presence of chitinous micro-pillar arrays adorning the insect elytron. (See image) To identify the presence of a structural absorption phenomenon, ultrastructural and optical studies are accompanied by FDTD simulations. Furthermore, various micro-pillar geometries and assemblies are compared by FDTD analysis to determine the optimal properties required for enhanced light absorption.
One of the main advantages of DNA nanotechnology is that colloidal nanoparticles and fluorophores can be positioned with nanometric precision. In order to fully manipulate the interaction between these species it is necessary to not only control their relative position but also their relative orientation. In this work, we study the orientation of Cy5 fluorophores incorporated in an innovative way using two independent measurements carried out in a standard wide-field fluorescence microscope. Our results show that single fluorophores attached with two anchoring points can adopt different orientations on a DNA-origami, from perpendicular to aligned with the double-helix depending on the number of bases removed from the complimentary sequence.
Mott insulators are archetypal examples of quantum materials. Some Mott insulators exhibit an drop in resistivity under the application of electric fields with durations of ~10 microseconds, with typical threshold fields of a few kV/cm. These electrical Mott transitions are volatile for fields just above threshold but become persistent for higher fields.
Electric fields of 1 MV/cm can be generated with ultrashort THz pulses, enabling the investigation of the sub-picosecond dynamics of the electric Mott transition. THz pulses can also be used to track the Drude conductivity of the material. We will present our results on THz driven dynamics in GaTa4Se8, a Mott insulator which exhibits clear electrical Mott transitions.
Time-resolved spectroscopies have provided various insights in the quest for understanding the fundamental properties of quantum materials and towards controlling their functional properties through light-matter interaction. In this regard, Free Electrons Lasers (FEL) have developed as a powerful tool to perform ultrafast X-ray spectroscopy allowing to obtain time-, energy- and momentum-resolved information.
In this contribution, I will introduce the SwissFEL soft-X-ray condensed matter experimental endstation, named Furka, which will be dedicated to time-resolved X-ray absorption (TR-XAS), resonant X-ray diffraction (TR-RXRD) and Resonant Inelastic X-ray Scattering (TR-RIXS) experiments to study correlated and quantum materials. Finally I will present the results of the very first commissioning experiments performed at Furka.
Magnetic switching by light remains little understood even after decades of study. Here we present a previously unexplored switching mechanism using X-rays on multiferroic (Ge,Mn)Te. It will be shown that the ferrimagnetic system can be reliably switched using stochastic resonance in XMCD and that the switching mechanism can be stopped by changing one of the two input frequencies. The observed collective switching indicates a spin-glass behaviour, which is supported by muSR results and further experimental and theoretical characterisation. The possibility to change the resonance conditions will allow to investigate the ultrafast magnetic switching and out of equilibrium magnetic order.
We highlight the current-induced modification of magnetism in the prototypical 5d Mott insulator Sr2IrO4 whose moments are entangled combinations of spins and orbitals. Based on an earlier report, oxygen octahedra can be rotated by applying electric current. Using muon spin spectroscopy, we further resolved an uncharted rotation of the magnetic moments. Such change is likely beyond the locking of iridium magnetic moments to the correlated rotation of oxygen octahedra and distinct from the strain-induced effect under the equilibrium condition. We show that a new state is created under the flow of energy in terms of electric current, which provides a way to switch the properties of this iridate on-demand.
The layered transition metal dichalcogenide 1$T$-TaS$_2$ has been studied intensively due to the interplay between structural transitions and the associated electronic phases. In the low temperature regime the monolayer behaves as a Mott insulator, while, when the bulk is considered, the electronic state is influenced by the presence of a strong bilayer hybridization favouring a band insulator groundstate. Recent equilibrium calculatons revealed that, depending on the sample termination, Mott physics is confined to the surface of the system. Starting from DFT-derived hoppings, we incorporate the effect of a realistic pulse excitation and study the production and diffusion of charge carriers in a layered setup.
Calculating the single-particle and two-particle correlations of interacting lattice systems in a consistent and con- serving manner is a challenging task. Nonlocal correlations play an important role in low-dimensional systems and in the vicinity of phase transitions and crossovers. We establish, use and implement the non-equilibrium framework of two methods that deal self-consistently with one-particle vertex corrections within the Hubbard model, namely the Two-Particle Self-Consistent approach (TPSC) and a variation of the latter (TPSC+GG). We employ them to study spin and charge susceptibilities upon quenching the system from 3 dimensions to 2, i.e from a cubic lattice to a square lattice.
Positronium being a purely leptonic atom provides an ideal test-bench of bound-state QED. Because of its simplicity, any deviation from calculations could hint to new physics beyond the standard model. A recent experiment exhibited a 4.2$\sigma$ discrepancy with QED in one of the 2S-2P fine structure transitions, deserving further investigation. This talk will present the ongoing experimental progresses made in the microwave 2S-2P and laser 1S-2S spectroscopy with the help of a pulsed slow positron beam at ETH.
The LEMING experiment aims to measure the free fall of muonium (M $= \mu^+ + e^-$) and would thereby test for the first time the weak equivalence principle using a purely leptonic, second-generation antimatter dominated system. Such a direct measurement is performed with atom interferometry, which requires a high-intensity, low-emittance M beam. This novel M source is being developed based on stopping accelerator muons in a layer of superfluid helium. In this contribution the LEMING experiment is introduced. The experimental setup for the first observation of M emitted from superfluid helium and an initial characterization of the novel M source are presented.
MuX, an experiment running at PSI, aims to measure the nuclear charge radii of radioactive isotopes such as $\mathrm{^{226}Ra}$ and $\mathrm{^{248}Cm}$ employing muonic atoms. The usage of such targets in the lab is limited to μg-quantities. Therefore, the formation of muonic radioactive atoms cannot be accomplished with standard methods using the direct muon capture in targets of hundreds of mg. A technique to transfer muons to μg-targets developed by the muX collaboration employs muon transfer chain reactions in a high-pressure cell filled with $\mathrm{D_2/H_2}$ gas. Measurements with $\mathrm{^{248}Cm}$ and $\mathrm{^{226}Ra}$ were performed in 2019 and are being analyzed. This contribution presents the status and the plans of the muX experiment.
The limit on the muon electric dipole moment (muEDM) could be improved by $\sim10^3$ with a dedicated muEDM Experiment at PSI. An EDM signal would be clear evidence of CP violation, while its absence at current sensitivity would constrain Beyond Standard Model theories. Simulations must incorporate multiple Coulomb scattering to determine its influence on design decisions. However, the underlying models at the relevant low momenta and material thicknesses require experimental verification. Multiple scattering of positrons and muons in graphite, pokalon and silicon was measured for momenta $50\,\mathrm{MeV}/c-140\,\mathrm{MeV}/c$. The measurements validate these models to inform the reconstruction efficiency for positron trajectories, an important systematic uncertainty in measuring EDM-induced muon spin precession.
The LHCb detector at CERN uses a magnetic field of bending power 4 Tm to measure properties such as charge and momentum of particles produced in collisions. An exact map of the magnetic field of the LHCb dipole improves the resolution and accuracy of these reconstructed properties, which greatly influence the precision of LHCb analyses. The development of the magnetic field map for Run 3 of the LHC, using finite element analysis (simulation) as well as field measurements taken in situ, is presented.
A new tracking detector (SciFi) has been installed in the LHCb experiment during the second Long Shutdown of the LHC. The SciFi tracker consists of three stations, each composed of four layers with dimensions of six by five meters. A system using opto-electronic BCAM (Brandeis CCD Angle Monitor) sensors was installed to provide long-term real-time 3D monitoring of the stations, which could suffer from movements or geometry deformations. The 3D positions of a dozen points spread over three SciFi layers are obtained by triangulation and monitored using eight cameras per layer. The intrinsic resolution of this system (~100microns) can be improved by averaging measurements taken during short periods of time.
We present a measurement of charm mixing and $CP$-violation parameters using $D^0\rightarrow K^0_S\pi^+\pi^-$ decays reconstructed in $pp$ collisions collected by the LHCb experiment from years 2016 to 2018. In particular, the analysis measures the dimensionless parameter $x$ related to the mass difference between the mass eigenstates of the $D^0$ meson. This was observed to be non-zero with a significance exceeding seven standard deviations in $D^{*+}\rightarrow\left( D^0\rightarrow K^0_S\pi^+\pi^-\right)\pi^+$ decay [PRL 127, 111801 (2021)]. We present here an independent measurement where $D^0$ candidates are reconstructed from $B^-\rightarrow D^{0}\mu^{-}X$ decays as the sample covers wider $D^0$ decay time distribution. A combination of the two analyses is performed to maximise the sensitivity.
Charmed baryon polarization is not predicted by theory and is a necessary input for the measurement of the charmed baryons magnetic dipole moment (MDM) which is foreseen at the LHC. The experimental status of the baryon MDM measurement using the bending crystal technology will be discussed. Furthermore, the measurement of $\Lambda^+_c $ polarization using $pp$ collisions data collected by the LHCb detector at a center of mass energy of 13 TeV will be presented; the polarization is extracted by means of a five-dimensional amplitude analysis of the three-body decay $\Lambda_c^+\rightarrow pK^-\pi^+$.
Only for participants who have registered and paid in advance. On-site registration is not possible.
Achieving the goals of the Paris Agreement to limit global warming to no more than 2°C above pre-industrial levels requires drastic cuts to CO2 emissions from fossil fuel use. The Enhanced Transparency Framework of the Paris Agreement requires all countries to provide transparent information on the implementation and achievement of their national objectives. The atmospheric science community supports this process by providing independent emission estimates based on atmospheric concentration measurements from ground-based networks and from space. Current and future satellites such as the European CO2 Monitoring mission CO2M provide a wealth of observations to estimate emissions from large point sources such as power plants and from cities and countries. In this presentation, I will provide an overview of existing and new satellites, explain how they retrieve trace gas concentrations from measurements in the SWIR range of the solar spectrum, and show examples of their capabilities and limitations to quantify emissions.
In this talk, I will describe recent experiments in atomically-thin transition metal dichalcogenides (TMDs) where Coulomb interactions between electrons dominate over their kinetic energy. Our measurements provide a direct evidence that the electrons at densities < 3 · 1011 cm-2 in a MoSe2 monolayer form a Wigner crystal even at B = 0 [1]. This is revealed by our low-temperature (T = 80 mK) magneto-optical spectroscopy experiments that utilize a newly developed technique allowing to unequivocally detect charge order [2]. This method relies on the modification of excitonic band structure arising due to the periodic potential experienced by the excitons interacting with an electronic lattice. Under such conditions, optically-inactive exciton states with finite momentum matching the reciprocal Wigner lattice vector k = kW get Bragg scattered back to the light cone, where they hybridize with the zero-momentum bright exciton states. This leads to emergence of a new, umklapp peak in the optical spectrum heralding the presence of periodically-ordered electronic charge distribution.
Twisted bilayers of TMDs in turn offer a wealth of new phenomena, ranging from dipolar excitons to correlated insulator states. Another striking example of qualitatively new phenomena in this system is our recent observation of an electrically tunable two-dimensional Feshbach resonance in exciton-hole scattering [3], which allows us to control the strength of interactions between excitons and holes located in different layers. Our findings enable hitherto unexplored possibilities for optical investigation of many-body physics, as well as realization of degenerate Bose-Fermi mixtures with tunable interactions.
The talk will give a short overview of the main activities of the Union, linking these to both past and current events in the world beyond physics.
Physics has historically been male dominated. This under-representation of women in physics was discussed at IUPAP’s General Assembly of 1999 and a resolution was passed to create a working group to survey the situation of IUPAP members, the Women in Physics Working Group (WG). This WG held its first International Conference on Women in Physics in 2002 in Paris and conducted its first survey. The WG held its 7th conference online in 2021, hosted by Australia, while the surveys have evolved to a Global Survey of scientists. Alongside these efforts IUPAP has sought to ensure its own committees and processes are more gender balanced, creating the role of Vice President Gender Champion in 2011. Much progress has been made but in an ever evolving landscape there is still much for IUPAP and society in general to do.
The mission of IUPAP (International Union of Pure and Applied Physics which I will describe) is to assist in the worldwide development of physics, to foster international cooperation (large scale physics projects is one way to do that) and to help in the application of physics towards solving problems of concern to humanity (connected to Basic Sciences for Sustainable Development which I will describe in my next talk).
To achieve this mission, IUPAP promotes Large Scale Physics Projects which are collective and inclusive, gathering physicists from all over the world beyond cultural, geographical and political differences. This has been shown to becoming more and more difficult in the present times and IUPAP helps, as much as it can, to overcome the difficulties.
IUPAP is the promoter and organizer of the International Year of Basic Sciences for Sustainable Development (IYBSSD). This International Year will span over 2022 and 2023 (Opening Ceremony in UNESCO Headquarters on July 8th 2022 in Paris, Closing Ceremony end of September 2023 at CERN in the new Science Gateway Building). Many events are expected to happen during 2022 and 2023. This International Year is perfectly in line with the mission of IUPAP to help in the applications of physics towards solving problems of concern to humanity.
On the example of Switzerland and the energy demand of 2019 the technical requirements and the economic consequences were analyzed for the transition from fossil fuels to renewable energy. The three energy systems based on electricity, hydrogen and synthetic fuels lead to the required photovoltaics for the electricity production and the size of the day/night and seasonal storage. The result is a completely electrified renewable energy economy is the most efficient and requires the installation of large storage capacities or the import of green hydrogen at least during the winter time.
In the last two decades attosecond pulses, driven by high harmonic generation, have become an indispensable tool in ultrafast science. However their usefulness is limited by both the highest achievable photon energy, and by the highest achievable flux. Both these limitations can potentially be circumvented using synthesized laser fields.
We report the generation of attosecond pulses with enhanced flux using a two-colour synthesized laser field. With attosecond streaking, we fully characterise the attosecond pulse and the synthesized field. Furthermore we present a novel three-colour synthesizer which we predict will enable cutoff and flux enhancement of isolated attosecond pulses.
Recently integrated THz detectors based on nonlinear polymers have shown high-sensitivity electric field measurements well-suited for quantum sensing. To expand its application for example to telecommunications a platform combining the ability of detection and emission of signals in the THz-frequency range is required. Since optical rectification - the typical nonlinear THz generation process - has a quadratic dependency on the pump signal, the low power resistance of nonlinear polymers prevents the development of efficient integrated on-chip emitters. Therefore want to combine this design with a more stable nonlinear material using the platform of thin-film lithium niobate for on-chip THz emission and detection.
Cooperative effects among electric dipoles lead to drastic changes in photon emission processes. Particularly, two types of cooperative emission, namely superfluorescence (SF) and spontaneous amplified emission (ASE), dominate the emission process from highly excited materials. Here, we investigated the photoluminescence (PL) dynamics in halide perovskite giant nanocrystals to scrutinize the contribution from the two cooperative processes. From the results of time-resolved PL spectroscopy, we observed that the dominant process gradually evolves from SF to ASE by increasing the temperature. Besides, we found the crossover regime of the two processes at the intermediate temperature of the transition. Our results will lead to a comprehensive understanding of cooperative effects in light-matter interactions.
Optical antennas have been widely used for manipulating single-molecule emission properties, including intensity, lifetime, spectrum, or directivity. Investigation of all these properties with high accuracy requires precise positioning of single molecules around the antennas, something experimentally challenging. Here, we make use of DNA origami as a breadboard to control the interactions between molecules and nanoantennas. By making use of a T-shaped structure, we can assemble both monomers and dimers of gold nanorods and precisely place the emitter at any desired position. We show, that we can affect the spectrum of a single fluorophore in a position-dependent manner, reporting excitation of either in-phase or antiphase plasmon modes in a nanorod dimer.
To approach the regime of single electron spectroscopy, we developed an asymmetric lens setup that makes the THz far-field resolution of single, strongly subwavelength meta-atoms possible.
Measuring the coupling of optical modes in complementary split-ring resonators (cSRRs) to two dimensional electron gases (2DEGs), we report normalized coupling ratios of up to $ \frac{Ω}{𝜔} =0.6$ in an InSb quantum well. Further, we can experimentally verify the quenching of superradiance in the single resonator system by quantifying the quality factors of the cavity resonances in arrays with decreasing resonator numbers.
The technique paves the way to couple sub-THz radiation to high quality, exfoliated 2D materials.
We experimentally and theoretically investigate the robustness of fermionic superfluidity to spin-dependent dissipation in a unitary Fermi gas. We measure the influence of local, controllable particle loss on the superfluid flow that occurs at a quantum point contact connecting two superfluid reservoirs. This flow is characterized by a non-Ohmic current-bias relation due to multiple Andreev reflections (MAR). Instead of a critical dissipation strength, we find the supercurrent decaying smoothly with increasing dissipation, indicating surprising robustness of MAR. A mean-field model qualitatively reproduces our observations. Our current work extends to pure spin transport under dissipation. These results are relevant for dissipative engineering of transport properties and understanding dissipative non-equilibrium superfluid systems.
Quantum computers require scalability as a key ingredient in order to perform complex and reliable calculations. A promising platform is the so called QCCD architecture, in which ion traps have multiple zones dedicated to specific quantum operations. In this perspective, I will describe work performed on a Paul trap which improves the control over multiple species ion crystals, including static confinement, shuttling through different zones, splitting crystals into smaller units and vice versa. These improvements naturally led to investigate new experimental regimes, in which different ion vibrational modes intersect and couple with a tunable strength.
The generalization of the notion of nonunitary superconductivity to complex materials with multiple internal degrees of freedom (such as orbitals, sublattices, or layers) opens multiple possibilities. Focusing on d-electron systems with two orbitals, we can address a variety of complex quantum materials and discuss the consequences for the superconducting spectra. In particular, gap openings of band crossings at finite energies can be attributed to a nonunitary order parameter if this is associated with a finite superconducting fitness measure. We speculate that nonunitary superconductivity in complex quantum materials is very common and can be associated with multiple cases of time-reversal symmetry breaking superconductors.
Transport of electromagnetic waves in 2D disordered hyperuniform structures shows an interesting behavior. Indeed, at least 5 different transport regimes have been recognized, like Anderson localization or diffusion. A traditionally used method to determine the transport regime associated with a wave function is the inverse participation ratio.
Unfortunately, this method leads to inconclusive results in this type of systems. To remedy this, a convolutional neural network is trained in order to predict wave functions transport regimes. We discuss the high prediction accuracy of the network and its generalization capability on similar systems.
We present a new diagrammatic Monte Carlo impurity solver based on the strong-coupling expansion of the vertex functions. By directly sampling the four-point pseudo-particle vertex diagrams and applying the self-consistency equation at the level of the triangular vertex, we significantly improve the traditional schemes such as non-crossing approximation, and achieve numerically exact results. We analyse the performance and the convergence rate of the impurity solver using exactly solvable models and observe that the efficiency of the vertex self-consistent scheme strongly depends on the particle statistics of the bath degrees of freedom. We discuss the physics of strong light-matter coupling in the spin-boson model representing an emitter in an optical waveguide.
Identifying relevant coarse degrees of freedom in a complex system is a key stage in developing effective theories. The renormalisation group provides a framework for this, but its practical execution in unfamiliar systems is fraught with ad-hoc choices, whereas machine learning approaches, though promising, often lack formal interpretability. Recently, the optimal coarse-graining rule was shown to be determined by a universal, but computationally difficult information-theoretic principle. Here we present the RSMI-NE algorithm employing state-of-art results in ML-based estimation of information-theoretic quantities, overcoming these computational challenges. We use it to develop a new paradigm in identifying the most relevant operators and their symmetries, conceptually paving the way towards automated theory building.
Laws of friction have been studied since 500 years, yet their microscopic underpinning still eludes us. We do not understand how slip events are nucleated, nor what controls the distribution of their magnitude; questions that are central in earthquake science. We provide a novel framework to capture these phenomena by considering how continuum descriptions (rate-and-state laws) are perturbed by disorder. It predicts the existence of power-law distributed slip events whose size diverges at a critical stress, and that nucleate global slip if they extend past a critical length. We confirm these predictions in a minimal model of a frictional interface.
Preparation of quantum states in form of a variational quantum circuit plays a crucial role in quantum computing. We show that, in addition to circuit architecture, the fidelity of the prepared state depends non-trivially on the number of circuit shots $N_s$ used in gradient descent. Namely, we observe that fidelity shows a critical behavior in $N_s$, giving rise to the notion of critical effective temperature, below which, the resource demand of optimization grows as $1 \sim \Delta^2$ with the system gap.
We analyze the effect of this dependence on the of large-scale simulations of frustrated magnets and provide a symmetry-enhanced simulation protocol reducing the computational costs in near-term quantum computers.
A subroutine of many quantum algorithms is the diagonalization of Pauli operators. Although it is always possible to construct a quantum circuit that simultaneously diagonalizes commuting Pauli operators, only resource-efficient circuits are reliably executable on near-term quantum computers. Generic circuits lead to a Swap-gate overhead on quantum devices with limited connectivity. A common alternative is excluding two-qubit gates which comes at the cost of restricting the class of diagonalizable sets to tensor product bases (TPBs). Here, we introduce a framework for constructing hardware-tailored (HT) diagonalization circuits. We group the Pauli operators occurring in the decomposition of popular Hamiltonians into jointly-HT-diagonalizable sets and observe that our approach can outperform conventional approaches.
Future experiments in high-energy physics demand large area and low cost silicon detectors with excellent time resolution. This talk will provide an overview of ongoing silicon sensor R&D projects aiming at high-precision timing.
Among them, the ERC Advanced MONOLITH project combines the advantages of monolithic standard CMOS processes with picosecond time resolution, offering a sustainable solution for the next generation of experiments for colliders, nuclear physics, cosmic-ray and solar physics. The precise time resolution is achieved using the novel Picosecond Avalanche Detector (PicoAD) sensor concept, that integrates a continuous gain-layer deep inside the sensor volume. A first, not yet optimised proof-of-concept ASIC shows full efficiency and 24ps time resolution.
The 100µPET project, a SNSF SINERGIA between UNIGE, EPFL and HUG, aims at producing a small-animal PET scanner with unprecedented volumetric spatial resolution by using multi-layer monolithic silicon pixel detectors.
The scanner will pioneer ultra-high-resolution molecular imaging, a field that is expected to have an enormous impact in medical applications.
The results of the R&D on the monolithic pixel ASIC’s optimization and the simulated scanner performance will be presented
The FCC-ee is the first stage of the Future Circular Collider program which envisions a new 100 km long circular collider ring. High-intensity collisions of electrons and positrons with energies of 90 to 365 GeV make the FCC-ee an electroweak, Higgs and top factory.
Especially the extremely large statistics at the Z-pole puts stringent requirements on the detectors. The innermost vertex detector has to precisely locate the collision vertices, while adding only a minimal amount of material to avoid multiple scattering deteriorating the detector performance.
This contribution discusses performance simulations of various vertex detector geometries and how depleted monolithic active pixel sensors (DMAPS) can fulfill the tight vertex detector requirements.
The FASER experiment at the LHC aims at searching for Long Lived Particles (LLP), not predicted by the Standard Model, produced in the very forward direction. The current detector is designed to identify LLP decaying into charged leptons, but is almost insensitive to neutral decay products.
Instrumenting the detector with a high precision W-Si pre-shower will allow for identification and reconstruction of electromagnetic showers produced by O(TeV) photons from LLP decays, at distances down to 200µm.
A description of the pre-shower and its expected performance will be presented along with results from pre-production prototypes of the SiGe HBT-based monolithic silicon pixel ASIC.
The High Luminosity LHC will increase the average number of proton-proton interactions per bunch crossing to 200. Consequently, material closest to the interaction points will receive a TID over one order of magnitude larger than seen previously. The ATLAS Inner Tracker (ITk) Pixel upgrade will be particularly affected by this increase in radiation dose. The impact of radiation damage on the ITk Pixel data transmission chain can be tested using the Bern medical cyclotron, an 18 MeV proton accelerator. This talk summarises the radiation hardness studies of the components used for this data transmission chain performed at the Bern cyclotron.
After Run III, the ATLAS detector will be upgraded to cope with the harsher radiation environment and increased proton interactions foreseen at High Luminosity LHC. Strict requirements on the quality of data transmission motivates the design of a highly ambitious data transmission system for the detector. The Optosystem performs optical-to-electrical conversion of signals from the pixel modules. This talk presents recent results related to the performance of the Optoboards, development of a GUI for their configuration and the design and production of the Optopanels.
The identification of mechanisms to stabilise quantum spin liquids phases is of prime interest. In non-Kramers pyrochlores, transverse fields were proposed as a possible route to promote quantum fluctuations in spin ices.
Such physics was also proposed to be at work in Tb$_{2}$Hf$_{2}$O$_{7}$, where experimental investigations have revealed the stabilisation of a spin liquid state despite a massive amount of structural disorder. We present a detailed structural analysis of this material based on neutron pair distribution function data, which we use to quantitatively relate to the magnetic properties.
The distribution of single-ion states, extracted from big-box modelling, provides additional insights to explain the observed peculiar correlated magnetic ground state.
We explore magnetic correlations in the recently identified topological kagome system TbMn$_{6}$Sn$_{6}$ using $\mu$SR, combined with local field analysis and neutron diffraction. Our studies identify an out-of-plane ferrimagnetic structure with slow magnetic fluctuations which exhibit a critical slowing down below T$^{*}_{C1}\simeq$ 120 K and freeze into quasi-static patches with ideal out-of-plane order below T$_{C1}\simeq$ 20 K. The appearance of the static patches sets in at a similar temperature as the appearance of topological transport behaviors. We further show that a hydrostatic pressure of 2.1 GPa stabilizes the topological ferrimagnetic ground state, giving rise to a magnetically-induced topological system whose magnetism can be controlled through disorder-free external parameters.
In La-based cuprate superconductors, doped charges are concentrated along domain walls between antiferromagnetic regions in the proposed stripe phase [1]. However, pinpointing the exact nature of this state is challenging as charge and spin density waves are always observed in a multidomain configuration.
Recently, uniaxial pressure was shown to detwin the charge density wave order into a single domain state [2]. Here we present neutron diffraction experiments which demonstrate that the spin density wave order parameter is also uniaxial, the two density waves are coupled, and the fundamental electronic order is a single-domain stripe state.
[1] Tranquada et al., Nature 375, 561 (1995)
[2] Choi et al., arXiv:2009.06967 (2021)
CeAuGe exhibits a ferromagnetic ordering below 10.2 K. Cu-doping in the Au site suppresses the unit cell volume, and the inversion symmetry is recovered from 50 % doped CeAuGe, while the ferromagnetic transition temperature remains similar. Neutron experiments reveal that magnetic structures of all Cu-doped CeAuGe compounds are collinear in-plane ferromagnetic. The resistivity of CeAuGe exhibits semimetallic behavior, while a resistive minimum is observed in CeCuGe due to the Kondo effect, meaning that the stronger Kondo hybridization in CeCuGe. In this presentation, we will discuss the ferromagnetic structures and electronic properties of small doped CeAuGe compounds, wherein the spatial inversion symmetry is still broken, and Kondo hybridization is enhanced.
Kagome antiferromagnets are well-established model systems in theoretical condensed matter research. Experimental verification of theoretical solutions is, however, lacking, as real systems obeying strict conditions of the ideal Kagome lattice are sparse. In the RAgGe family of compounds, frustrated magnetism is induced by the distorted Kagome arrangement of the rare earth R$^{+3}$ ions, influenced by strong magnetic easy-axis anisotropy and itinerant electrons. Here, we present single crystal neutron diffraction results for the R = Yb and Tm compounds and discuss approaches to investigate possibilities of topological and multi-k feature.
$TmB_{4}$ is a member of rare-earth tetraborites family where $Tm^{+3}$ ions can be topologically mapped to a Shastry-Sutherland lattice,it has few magnetic phases with plateaus in magnetisation, among them the 1/8 plateau phase is a meta-stable phase and reported to depend strongly on the temperature and history of the system. In order to study this phase using with neutrons scattering we developed a setup to measure macroscopic properties of the sample in-situ during the neutron scattering experiment. This will provide information about the phase transitions and helps accurate intensity assignment of the intensities for scans.
The Paul Scherrer Institute operates a Ultracold Neutron (UCN) source based on solid deuterium as a moderator and UCN converter. UCNs are storable for several minutes. This makes them uniquely suitable for measuring fundamental properties of the neutron, such as the search for the neutron electric dipole moment, in the n2EDM experiment.
It is essential to increase experimental statistics. Therefore, we work to better understand the UCN source and increase the UCN intensity delivered at the beam ports. Candidate areas for improvement are the quality of the deuterium crystal and the UCN transport. This talk will explain the UCN source, and give an overview of our improvements.
The neutron Electric Dipole Moment (EDM) represents a promising channel for finding new physics beyond the Standard Model. The existence of a neutron EDM violates the combined symmetries of Parity (P) and Charge conjugation (C) invoking CPT-symmetry. This new source of CP violation could help to explain the baryon asymmetry of the Universe. The present-best upper limit of 1.8∙10-26 e·cm (90% C.L.) was set by the international nEDM collaboration. The next-generation n2EDM experiment, currently under construction at the ultracold neutron source at the Paul Scherrer Institute, aims to search for an EDM with one order of magnitude improved sensitivity. In this talk, an overview of the experiment will be presented.
Frequency dissemination in phase-stabilized optical fiber networks has become a state-of-the-art tool for metrological frequency comparisons and precision measurements. The recently established Swiss frequency metrology network spanning 456 km of fibers connects METAS to the University of Basel and ETH Zurich. This network enables dissemination of optical frequencies, referenced to the SI-traceable atomic clocks from METAS, to precision spectroscopy laboratories at the universities, with a fractional frequency link instability as low as $3.8\times10^{-19}$ at 2000 s integration time. We report on the state of the network and demonstrate its application in an SI-traceable measurement and stabilization of the absolute frequency of a spectroscopy laser in a remote laboratory.
Strong coupling of a cavity photon to an exciton in semiconductors leads to the formation of exciton-polaritons, light-matter quasiparticles that can undergo Bose-Einstein condensation (BEC). Patterning a length-tunable cavity by Focused Ion Beam milling allows engineering potential landscapes to trap these condensates and emulate different Hamiltonians. Here, we investigate a 1D polariton lattice with alternating coupling strengths, a so-called Su-Schrieffer–Heeger chain. Atomic Force Microscopy has been used to examine the structures, continued by optical characterization, indicating the formation of topological edge states in the lattice. Furthermore, we discuss our progress on demonstrating selective condensation in different lattice modes.
We study Ramsey-type pulsed interrogation in a micro-fabricated Rb vapor cell for novel miniature atomic clocks called the $\mu $POP clock. Pulsed interrogation reduces light shift effects, allowing for improved long-term stability. The exploitable Ramsey free evolution time and thus the achievable Ramsey signal and clock stability are limited by the $\approx$ 4 – 5 kHz relaxation rates of the Rb atoms in the mm-scale cell. These relaxation rates are measured using a clock-type signal acquisition scheme. Experimental signals and their impact on the $\mu $ clock stability will be discussed. They allow for an experimental clock stability around 1×10^-11 at 1 second and few 10^-12 at one day timescale.
Three-level atomic systems coupled to light have the capacity to host dark states. We study a system of V-shaped three-level atoms coherently coupled to the two quadratures of a dissipative cavity. The interplay between the atomic level structure and dissipation makes the phase diagram of the open system drastically different from the closed one. It leads to the stabilization of a continuous family of dark and nearly dark excited many-body states with inverted atomic populations as the steady states. The multistability of these states can be probed via their distinct fluctuations, excitation spectra, and Liouvillian dynamics which are highly sensitive to ramp protocols.
I will present the results obtained with our cavity-QED experiment, where we trap fermionic Lithium atoms in an optical resonator to perform quantum simulations.
I will focus on the simulation of random spin models with long-range spin-exchange interactions. We implement these models by trapping a chain of atoms with tunable random transition frequencies in a cavity. The tunability is achieved by locally light-shifting the excited state of the atoms. In this scenario, we studied the competition between the collective many-body physics and disorder.
Furthermore, I will discuss possible perspectives of using our light-shifting technique for the quantum simulation of holographic matter such as the SYK model.
A few years ago [1], it was proposed that materials hosting narrow topological bands can support nontrivial superfluid weight, with Tc beyond the conventional BCS limits. This behavior roots to the large spread of electronic orbitals in topological bands, which is linked to properties of quantum metrics associated with electronic Bloch states [2,3]. We present a new perspective for quantum transport in flat band materials, adding strange metallicity, anomalous Hall conductance, fractional quantum Hall effect, thermoelectricity, and quantum noize, — to a common denominator from the quantum-geometric point of view.
[1] S. Peotta, P. Törmä, Nature Commun. 6, 8944 (2015). [2] N. Marzari, D. Vanderbilt, Phys. Rev. B 56, 12847 (1997). [3] A. Kruchkov, Phys. Rev. B 105, L241102 (2022).
We observe how vacuum cavity fields modify magneto-transport in the integer quantum Hall effect. In particular, odd filling factors lose their quantization, while fractional states remain intact. We quantitatively describe this loss of quantization as vacuum field induced resistivity. In our interpretation the interaction with vacuum fields adds a long range perturbation to the system, making it possible for electrons to scatter in between edge and bulk states via an intermediate state containing a virtual particle. This process ultimately breaks the topological protection of the edge states.
Endofullerenes are candidate systems for molecular spintronics and electronics. Ho3N@C80 has been studied using x-ray absorption spectroscopy (XAS) at different temperatures with a low noise Everthart-Thornley detector at the PEARL beamline of the Swiss Light Source. Molecules were air-brushed on a graphene substrate, then introduced into vacuum and annealed. X-ray photoelectron spectroscopy indicates a monolayer of molecules. XAS at the Ho M45 edge is performed at different temperatures with per mille accuracy. Multiplet theory predicts the spectra as a function of the orientation of the plane spanned by the three Ho atoms in the molecules.
K3+xC60 film exhibits Mott transitions and superconductivity, depending on dimensionality and doping. Surprisingly, in the trilayer case, a strong electron-hole doping asymmetry has been observed in the SC-phase absent in the bulk. Using DFT+DMFT, we show this doping asymmetry results from a substantial charge reshuffling from the top layer to the middle layer. While the nominal filling per fullerene is close to n=3, the top layer rapidly switches to an n=2 insulating state upon hole doping, which implies a doping asymmetry of the SC gap. The interlayer charge transfer and layer-selective metal-insulator transition result from the interplay between crystal field splittings, strong Coulomb interactions, and an effectively negative Hund coupling.
Among first row transition metal oxides, the perovskite oxide SrCrO3 (SCO) remain only vaguely explored. Its properties are still controversial and under debate. Interestingly, this compound has been observed to be metallic and antiferromagnetic at the same time. The goal of this study is to uncover the electric behaviour of SCO thin films as function of strain. Temperature-dependent transport measurements of SCO films grown by RF magnetron sputtering show a strain-driven metal-to insulator transition under application of strain. Recent results of DFT calculations show that tensile strain is responsible for lifting the degeneracy of the t2g orbitals and promoting orbital ordering, resulting in the opening of an energy gap.
I will present muon spin rotation and magnetic susceptibility experiments on in-plane stress effects on the static spin-stripe order and superconductivity in the cuprate system La$_{2-x}$Ba$_{x}$CuO$_{4}$ with $x=0.115$ [1]. An extremely low uniaxial stress of ${\sim}$0.1 GPa induces a substantial decrease in the magnetic volume fraction and a dramatic rise in the onset of 3D superconductivity, from $\sim10$ to 32~K; however, the onset of at-least-2D superconductivity is much less sensitive to stress. These results show not only that large-volume-fraction spin-stripe order is anti-correlated with 3D superconducting coherence, but also that these states are energetically very finely balanced, imposing an important constraint on theoretical models.
[1] Guguchia${\sim}$et.al., Phys.${\sim}$Rev.${\sim}$Lett. 125, 097005 (2020).
We use finite-temperature tensor network algorithms to investigate the spin-1/2 J1−J2 Heisenberg model on the square lattice. We provide strong numerical evidence in favor of an Ising transition in the collinear phase of the model, confirming a 30 years old field theory prediction. In units of J2, the critical temperature reaches a maximal value of Tc/J2≃0.18 around J2/J1≃1.0. It is strongly suppressed upon approaching the zero-temperature boundary of the collinear phase J2/J1≃0.6, and it vanishes as 1/log(J2/J1) in the large J2/J1 limit. We stress the importance of symmetry implementation and discuss the new perspectives in the investigation of the thermal properties of quantum Heisenberg antiferromagnets.
In 2022 the LHCb experiment starts taking data using a redesigned data acquisition and trigger system. A complete event reconstruction at the full LHC bunch-crossing rate of 30MHz will be performed using a two-stage software trigger, using GPUs in the first stage and a farm of CPUs in the second stage.
I will show the performance and design of the real-time event reconstruction, discuss the challenges of implementing and running a purely software-based trigger at an LHC experiment and present first results from Run 3 data taking.
PLUME is a new sub-detector built for the LHCb experiment for the upcoming Run-3, to perform high-precision luminosity measurements for LHCb and LHC feedback. An overview will be given of the detector and its principles, with a spotlight for the monitoring system constructed at EPFL. This system allows for stable operation of the detector in the extreme environment around 1m upstream of the collision point. First data will be shown together with its performance, collected during the start-up taking place over April and May 2022.
The Dark Matter Particle Explorer (DAMPE) is a space-based cosmic ray observatory with the aim, among others, to study cosmic ray electrons (CREs) up to 10 TeV. Due to the low CREs rate at multi-TeV, we increase the acceptance by selecting events outside of the fiducial volume. High incidence events do however require special treatments with sophisticated analysis tools. We propose therefore a Convolutional Network to identify non-fiducial CREs and reject background, based on their interaction in DAMPE calorimeter. We will show how this method can outperform classical methods.
The Penetrating particle ANalyzer (PAN) is a multidisciplinary instrument designed to operate in space and precisely measure and monitor the flux and composition of highly penetrating particles of energy ranging from 100 MeV/n to 20 GeV/n, filling the current observational gap in this energy interval. PAN is a modular design magnetic spectrometer based on a high-resolution silicon tracker, which allows for easy implementation in different missions and space environments.
In this talk, the development status of the smaller dimension demonstrator, mini.PAN, and the results obtained by the beam tests are reported. Possible applications are discussed as well.
Neutron grating interferometers can be employed as powerful tools to perform high-precision measurements of deflection angles and scattering. A novel concept of a symmetric Talbot-Lau interferometer using absorption gratings is under development at the University of Bern. The ultimate goal of this project will be a sensitive measurement of the neutron electric charge. Currently, a proof-of-principle apparatus is being investigated at the cold neutron beamline BOA at the Paul Scherrer Institute. In this presentation, first experimental results concerning the setup, the alignment procedure, and the achievable sensitivities will be presented.
The n2EDM experiment searching for the neutron electric dipole moment is currently being commissioned at PSI. Essential for a tenfold sensitivity improvement relative to the current best result is a uniform magnetic field, since any magnetic contamination of the apparatus may result in a systematic error of the measurement.
Parts in the direct vicinity of the neutron precession chamber need to be non-magnetic at a level of a few pT at 5cm distance from the surface. Therefore, the collaboration is building a new high-sensitivity gradiometer using laser-pumped caesium magnetometers to qualify all parts installed in the experiment. I will present the concept and status of the new device.
The existence of a non-zero neutron Electric Dipole Moment (EDM) would violate CP symmetry and might help in the understanding of the apparent baryon asymmetry in the universe. The BeamEDM experiment aims to measure the neutron EDM using a novel technique which overcomes the systematic limitations of previous neutron beam experiments. BeamEDM exploits the time-of-flight technique with a pulsed neutron beam which allows to distinguish time-dependent from time-independent effects, e.g. an EDM. A proof-of-principle apparatus has been developed to perform preliminary measurements at the Institut Laue-Langevin. The future full-scale experiment is intended for the European Spallation Source.
Parity-conjugated copies in the weak interactions of Standard Model particles, so called mirror-particles, could provide answers for several standing issues in physics today. Mixing between neutrons and mirror-neutrons in particular would violate baryon number conservation, a necessary ingredient for baryogenesis.
The mirror-neutron experiment at PSI searches for neutron to mirror-neutron oscillations in the presence of a non-zero mirror magnetic field by looking for anomalous neutron losses of stored ultracold neutrons (UCN). Data-taking was completed in 2021 and the analysis is ongoing. We present the analysis principle, based on Monte Carlo simulations and precise magnetic field maps, and show preliminary results.
Bragg edge imaging (BEI) is based on the wavelength-dependent effect of neutron diffraction at crystal lattice planes on the neutron transmission spectrum. The wavelengths of discontinuities, Bragg edges, in the neutron transmission spectrum due to Bragg scattering of polycrystalline materials directly relate to respective lattice spacings, allowing crystalline phase identification and lattice strain characterisation, while the overall pattern provides information of other microstructural features, such as grain size and texture variations. On the other hand, for single or oligo-crystalline materials BEI allows to index and map grains and orientation distributions. Here we will present different examples involving the application of BEI for advanced microstructural characterisation of engineering materials.
Gadolinium (Gd) salt solutions are paramagnetic liquids that can be manipulated by magnetic field gradients. Apart from possessing a large magnetic moment, Gd has the highest neutron absorption cross section of all naturally occurring elements. Neutron imaging was employed to investigate the effect of the magnetic force by mapping Gd$^{3+}$ concentration evolutions. It was demonstrated that salt fingering instabilities can be prevented by magnetic field gradients when a paramagnetic component is present. Further experiments tracked the uptake of Gd$^{3+}$ ions by porous carbon aerogel electrodes during capacitive deionisation processes. This injection of electrical energy gave rise to systems in which the magnetic field gradient could modify mechanical equilibrium.
Fast neutrons offer high penetration capabilities for both light and dense materials due to their comparatively low interaction cross-sections for which X-rays or thermal neutrons do not provide sufficient penetration. One of the main factors, preventing the widespread application of this technique, are limitations of current fast neutron detectors, including low efficiency, high light-scattering medium, long-lived afterglow. In an attempt to overcome these drawbacks, a new class of scintillator, colloidal perovskite nanocrystals, is being explored. The light yield, spatial resolution, and neutron-vs-gamma sensitivity are determined for halide-based perovskite nanocrystals (including FAPbBr3 and Mn2+-doped CsPb(BrCl)3), and compared with traditional phosphor ZnS:Cu.
For polycrystalline materials, material properties including strength, deformation behavior, and stress corrosion cracking resistance depend on the texture of the crystalline microstructure. Conventional assessment of texture is either limited to thin surface regions or it is destructive. Only X-ray diffraction and neutrons enable quantitative studies of bulk texture. Here, we report how transformative progress in advanced Laue three-dimensional neutron diffraction tomography enables to map several hundred grains and, thus, allows grain orientation assessment in the volume of centimetre-sized samples with statistical significance. The short exposure times and non-destructive nature of Laue3DNDT support in-situ studies, while future improvements in spatial resolution shall include more accurate grain morphology in corresponding studies.
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