Description
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.
Here we study the anomalous interface magnetic excitations in the YBa2Cu3O7/manganite heterostructures. Detailed analysis of the inelastic part of the high-resolution Resonant Inelastic X-ray Scattering (RIXS) signal in conjunction with polarimetry show the presence of two magnon modes in the cuprate, including a unique, non-dispersive interface magnon, that appears only due to the interfacial...
In the search for Quantum Spin Liquid (QSL) phases, Rare-Earth pyrochlores are of interest to stabilize Spin Ice states. In QSL candidates, magnetic neutron scattering is a well-established probe for studying magnetic order and interactions. However, in rare-earth elements, degrees of freedom can include magnetic and electric multipoles, which are elusive in scattering experiments. Then, bulk...
Large amounts of waste heat generated in our economy could be converted into useful electric power using thermoelectric generators. However, the low efficiency, scarcity, high cost, and poor production scalability of conventional thermoelectric material hinder their mass deployment. Nanoengineering has proven an excellent approach for enhancing the thermoelectric properties of abundant and...
Quantum spin ladders are fascinating systems with complex excitation spectra that depend on the relative strengths of the leg and rung exchange interactions. Here we report the magnetic properties of a new strong-leg spin ladder obtained by using magnetization, specific heat and neutron scattering measurements. In particular, we performed comprehensive inelastic neutron scattering experiments...
The exact symmetries and form of the cooper pair wave function in many unconventional superconductors remains subject of ongoing debate. A possible way to shed some more light upon the matter is by explicitly computing thermodynamic properties given a functional form of the order parameter as well as a microscopic description of the normal state of a material. One such quantity is the upper...
The properties of stable Luttinger liquid phases in models with a non-conserved number of particles are investigated. We study Luttinger liquid phases in one-dimensional models of hard-core boson and spinless fermion chains where particles can be created and annihilated three by three on adjacent sites. We provide an intuitive and systematic method based on the flow equation approach, which...
We propose a variant of the corner transfer matrix renormalisation group algorithm that contracts infinite tensor networks on the honeycomb lattice. We then apply the algorithm to the conceptually simple yet numerically challenging problem of the triangular lattice Ising antiferromagnet in a field at low temperatures and magnetic fields. We study how the finite temperature three-state Potts...
Convergent beam electron diffraction (CBED) on 2D materials provides a method for high-resolution imaging of individual particles deposited on a 2D material. A single-shot CBED pattern combines a diffraction pattern and a defocused image of the sample. We are investigating the optimal experimental imaging conditions for CBED of nanoparticles deposited on graphene. CBED allows regulating the...
We study the spin-1/2 Heisenberg model on the square lattice with ferromagnetic nearest-neighbor coupling $J_1 < 0$ and frustrated antiferromagnetic next-nearest coupling coupling $J_2 > 0$. For spin-1/2, the zero-temperature phase diagram differs from the $J_1 < 0$ case, with a first order transition to the ferromagnetic state.
By combining tensor network methods and spin wave theory, we...
Recent advances have turned the scanning tunnelling microscope (STM) into a single molecule identification tool. We apply a radio frequency STM to excite a single molecule junction based on a polar substituted helicene molecule by an electric field oscillating at 2 to 5 GHz. We detect the dielectric relaxation of the single molecule junction indirectly via its effect of power dissipation,...
With the goal of controlling the skyrmion density and their formation mechanism, which are highly relevant for spintronic devices using skyrmions, we investigate $[Ir(1nm)/Co(t)/Pt(1nm)]_n$ multilayers with varying Co-layer thickness. We observe that by increasing the Co layer thickness, domains (at zero field) become narrower, and skyrmion density (in an applied field) increases. This can be...
We report the direct XPEEM imaging of the magnetic response of a 4.8nm La$_{0.9}$Ba$_{0.1}$MnO$_3$ film to the voltage applied across a 5nm BaTiO$_3$ film. Ferroelectric patterns were written on the BaTiO$_3$ with an AFM in contact-mode and the change in magnetic contrast measured with XPEEM. We observe an increase in the magnetic contrast when going from negative to positive writing voltages...
Towards a next-generation rare pion decay experiment located at PSI.
The Alpha Magnetic Spectrometer operating on the International Space Station is a cutting-edge detector that is measuring spectra of cosmic ray particles and nuclei, including the isotopic composition of light nuclei, which is essential to understand cosmic ray propagation and origin. The 10Be/9Be ratio measures the cosmic ray propagation volume in the Galaxy, and the 6Li/7Li ratio tests the...
The experiments at CERN’s Antiproton Decelerator detect antimatter through its annihilation, making the antiproton-nucleus ($\bar{p}A$) interaction one of the main processes of interest. As the annihilation mechanism itself is not well understood, a beamline for sub-keV antiprotons is built at the ASACUSA facility to measure the $\bar{p}A$ annihilation at rest for a variety of nuclei....
DARWIN is a proposed next-generation dark matter observatory that aims to detect Weakly Interacting Massive Particles (WIMPs) using 40t of instrumented liquid xenon. Due to its large dimensions together with the technical and scientific challenges involved, Xenoscope, a full-scale vertical demonstrator, was built to test and refine the necessary technologies. This prototype was constructed to...
A positron trap is a powerful tool for performing experiments with positrons and positronium. This type of device can typically produce ~105 e$^+$/s in bunches with a diameter of 1-2 mm and an energy spread of approximately 50 meV.
We aim to use these positron pulses to observe molecules containing positronium, such as PsH and PsO via collisions in gases such as methane and carbon dioxide. ...
We present a measurement of the Branching Fraction $\mathcal{B}(B^+\rightarrow \overline{D^0} K^+)$ using $186.75 \,\, \text{fb}^{-1}$ of $\Upsilon(4S)$ Belle II data gathered from 2019 to 2021. To extract the signal yield, we fit over reconstructed events corresponding to $B^+ \rightarrow \overline{D^0} K^+$ with $\overline{D^0} \rightarrow K^+ \pi^-$ which are distributed over the $beam$ to...
We demonstrate laser-cooling of Ca+ ions confined in a segmented linear Paul trap and in presence of a strongly inhomogeneous magnetic field. We show that by employing two cooling lasers with properly adjusted wavelengths and polarizations, the trapped ions can efficiently be cooled to millikelvin temperatures despite strong position-dependent Zeeman shifts. The experimental results are...
Ultracold ions in linear radiofrequency traps are well-established and highly controllable quantum systems with a variety of applications in the quantum sciences. The combination with a charged nanomechanical oscillator may offer novel ways for state preparation and readout by coupling both systems within a single quantum device.
Here we demonstrate the transfer of energy from a mechanically...
Complex energy-level structure of molecules with rotational and vibrational degrees of freedom provides transitions with various properties but also presents challenges toward molecular state initialization, manipulation, and readout. We followed a quantum-logic protocol that uses a single co-trapped atomic ion as a probe for the molecular state, and demonstrated a quantum non-demolition state...
Complete control over the quantum state of single molecules possesses significant challenges due to the complexity of their energy level structure and was demonstrated only recently for diatomic molecular ions. We report on the progress of a generalization of a quantum control scheme that employs quantum logic spectroscopy with a co-trapped atomic ion of calcium to polyatomic molecules. This...
In interstellar space, reactions involving neutral dipolar molecules and ions are the main mechanism with which new molecules are formed, yet there is sparse data about reactivities in this range.
Here we present an experiment aimed at studying radical-ion reactivities at conditions relevant for astrochemistry --high vacuum and temperatures down to few Kelvins.
A Stark decelerator slows down...
Permanent electric dipole moments have been found to significantly reduce the interference contrast in molecular diffraction experiments at nanomechanical gratings. Dephasing caused by the interactions with implanted charges in the nanogratings has been presented as a possible explanation for this behavior. Here we investigate the polarity of 6,11-dihydroxy-5,12-naphthacenedione, which could...
Quantum gas experiments provide the unique opportunity to study complex quantum many-body systems. Starting from a dilute gas non-local, all-to-all interactions can be implemented by means of a high-finesse optical cavity.
In our experiment we prepare a degenerate, strongly interacting Fermi gas of Li 6 atoms trapped inside a high-finesse optical cavity. We induce long-range atom-atom,...
We envision preparing mesoscopic motional quantum states by coupling the motion of a levitated particle to a trapped ion qubit.
First, we levitate a charged silica nanoparticle in a Paul trap in ultra-high vacuum resulting in an ultra-high quality factor (Q=1.6(4)×10^10) of mechanical oscillations.[1]
Second, we control the particle’s center-of-mass motion by applying measurement-based...
The scalar magnetometer on board ESA's JUICE mission is an optically pumped magnetometer, based on the coherent population trapping (CPT) effect in the atomic vapour of the rubidium isotope 87. The CPT effect is a quantum mechanical interference effect which allows the precise detection of the external magnetic field strength by measuring the so-called Zeeman shifts. The instrument excites and...
Lattice-matched interfacing of two large band-gap semiconductors such as AlN, AlGaN, and GaN can induce high-mobility electron and hole charge carriers without addition of dopants. Determining this phenomenon are the pseudomorphic strain and the spontaneous polarization along the (0001) direction. To access the physics of the interfacial charge carriers confined in quantum-well states, we have...
Sr2IrO4 is a layered perovskite isostructural to the cuprate superconductor La2CuO4. The combination of strong spin-orbit coupling inherent to Ir4+ ions and modest Coulomb interaction induces a Mott insulating ground state with Heisenberg spin dynamics. Theses striking similarities with cuprates extend to the unusual metallic state of lightly doped Sr2IrO4 characterized by Fermi arcs and a...
Artificial spin ices are arrays of nanomagnets, which are coupled through dipolar interactions. The kagome artificial spin ice is the archetypal, highly frustrated example. It is predicated to exhibit a rich phase diagram but the ground state proves difficult to reach. In this project, we investigate how the presence of a cobalt underlayer and a platinum spacer affects the interactions between...
We report the nonlinear spin-wave transport in the array of the ten and ninety 260 nm wide YIG nano-waveguides. A new method based on Ar+ ion beam etching was developed for the nano-waveguide fabrication using a positive CSAR resist as a hard mask. For generating and detecting spin waves, 2 µm wide microwave antennas spaced 5 µm apart are used. The propagating spin-wave spectroscopy is...
Despite more than two decades of research, the proposed microscopic mechanisms underpinning laser-induced ultrafast demagnetization in magnetic thin films are not fully established. Little attention has been paid so far to nano-sized systems, where dipolar coupling and shape anisotropy may play an important role.
We show that the optically-induced ultrafast magnetization suppression in arrays...
Magnetic interlayer couplings are widely explored in spintronic architectures, while the lateral couplings are rarely studied. Here we demonstrate a lateral interfacial exchange coupling based effect in ferrimagnetic thin film systems by patterning the device into regions with different compensation temperatures via oxidation and He+ irradiation. We show that the coupling induced exchange bias...
Exploration of high-frequency magnetization-dynamics in three-dimensional (3D) magnetic nanostructures may lead to paradigm-shifting in next-generation spintronic and magnonic devices. Despite remarkable progress in fabrication$^{1}$, the measurement and interpretation of magnetization-dynamics in 3D magnetic structures has remained challenging. Here we present the measurement of coherent...
Artificial spin ices are arrays of dipolar-coupled single domain nanomagnets, which exhibit rich behaviour. We study a family of artificial spin ices, formed by placing out-of-plane nanomagnets on the vertices of the Archimedean lattices. By demagnetising these arrays using field protocols and imaging their configuration using magnetic force microscopy, we observe different types of magnetic...
Metastable magnetic topological textures are of high interest to the spintronics community, in part because may find applications in future magnetic data storage technologies. NdMn2Ge2 is a rare-earth complex noncollinear ferromagnet, which has been shown to host metastable skyrmions at room temperature with no applied magnetic field. Here we, present a scanning transmission x-ray microscopy...
Low doping electron-electron interactions in monolayer MoS$_2$ lead to a ferromagnetic spin order,whereas larger occupation of spin-polarized energy bands results in paramagnetism. The electron density of MoS$_2$ might be tuned with gate voltage, thus providing the switch ability of the ferromagnetic to paramagnetic first-order phase transition. An abrupt phase transition in two-dimensional...
A requirement for the realisation of large-scale magnon-based circuits is the low-loss excitation and detection of spin-waves. To minimise radiation losses and to approach single magnon level, an efficient coupling of high frequency microwave signals to propagating spin waves is required. In particular, large-area impedance-matched and on-chip lithographed nanoantennas are necessary.
Here we...
Artificial spin ice are arrangements of dipolar coupled nanomagnets, which exhibit a range of interesting behaviour. Here, we study an artificial spin ice based on the ruby lattice. This pattern has a complex unit cell with 12 nanomagnets and two lattice constants that define it. By varying the two lattice constants independently, we can change the interaction between nanomagnets. Using x-ray...
Artificial spin ices are arrays of strongly-correlated nanomagnets, which provide a valuable platform to study phase transitions. The kagome artificial spin ice is a highly frustrated example that undergoes two separate ordering transitions. We show how rotating each nanomagnet in the kagome lattice about its centre allows us to access a rich phase diagram. Using a combination of magnetic...
We present a study on the effective propagation of spin waves in curved nano-conduits made of Gallium-substituted Yttrium Iron Garnet (GaYIG) using micro-focused Brillouin Light Scattering spectroscopy. The investigation was carried out in the Forward Volume geometry to ensure an isotropic in-plane medium for spin-wave propagation. The curved nano-conduits have a thickness of 69 nm and a...
Over the past decade of spintronics research, spin-orbit torque (SOT) has emerged as an ultrafast and energy efficient method for electrically switching magnetizations. Ultrathin heavy metal/ferromagnetic bilayers have been the subject of particular interest, due to the strong spin-orbit coupling in heavy metals, as well as having many materials engineering opportunities to tune the SOT. One...
Magnetization curves recorded with X-ray magnetic circular dichroism on samples with a few % of a monolayer (ML) of Dy atoms on highly oriented pyrolytic graphite (HOPG) indicate two distinct magnetic species with mutual antiferromagnetic interactions. To understand the origin and magnetic interactions of the species, spatial distributions of Dy atoms and small clusters were studied using...
Storing information in magnetic bits requires excellent control over their nanoscale magnetic properties. A prime example of this challenge are STT-MRAM (spin transfer torque magnetic random access memory) devices - which have rather high failure rates. In order to investigate the sources of potential failure, a technique that can resolve small magnetic fields with high spatial resolution is...
Frappy is a python framework to implement a device communication and
abstraction layer for complex sample environment equipment such as
cyostats, cryomagnets, furnaces, humidity chambers and for the integration
of measurement devices. It is designed to build up complex setups for
beamline experiments as well as for lab based measurements. It enables
users of large scale facilities to...
High-precision measurements of angular correlations in neutron beta decay are at the forefront of particle physics. For a new generation of beta decay experiments, like the PERC (Proton Electron Decay Channel) experiment under construction in Munich, frequency-based beta spectroscopy methods using the cyclotron radiation emitted by electrons in a homogeneous magnetic field have been emerging...
The n2EDM experiment searches for the neutron electric dipole moment, which could help understand the baryon asymmetry of the universe. To allow for high precision measurements, an active magnetic shielding (AMS) and a magnetically shielded room (MSR) for passive shielding ensure a magnetically controlled volume.
Using the AMS coil system external magnetic fields can be compensated. The...
Correlated materials often exhibit co-existing or competing quantum phases. An open question is whether the dominant phase eliminates the other one prior to its emergence. Here, I present a high resolution time-of-flight neutron spectroscopy study on the low-energy incommensurate spin excitations of superconducting $La_{1.855}Sr_{0.145}CuO_{4}$. We find that the spin excitations observed above...
Climate change necessitates a reduction of fossil fuel usage. Particularly, transport relies primarily on fossil fuel. Electric vehicles are key to reduce this reliance. As part of an interdisciplinary project, we aim to develop more efficient electric drives using magnetic flux guidance in the rotor by targeted residual stress instead of cutouts. Increasing the maximum achievable rotational...
For polycrystalline materials, key material properties depend significantly on the texture of the crystalline microstructure. Conventional assessment of texture is either limited to surface regions or it is destructive, probing small fractions of a specimen. Only high energy X-rays and neutrons enable quantitative studies of bulk texture. Here, we report how transformative progress in Laue...
Understanding mechanisms of energy dissipation is nowadays successfully examined down to the atomic level by means of Atomic Force Microscope (AFM). Graphene bilayers with twist angles are known to host the series of interaction-driven correlated insulating phases with promising applications for nano-electronics, etc. The electron interactions might even lead to the emergence of magnetism,...
We demonstrate an operational sweet spot for a Ge/Si core/shell nanowire hole spin qubit, for which both Rabi frequency and spin echo coherence times show a maximum. It is related to the optimal operation point theoretically predicted for hole spins in the group IV crystals. Fitting measured data to a simple model we were able to extract the intrinsic g-factor and estimate the spin-orbit...
We characterize the Ge/Si core/shell nanowires extracting their field effect mobility for various growth parameters. For this, COMSOL simulations are performed to calculate numerically the backgate-to-nanowire capacitance of a realistic device. The observation of sweet spots of the Hahn-echo coherence time of a qubit formed in such a nanowire suggests the presence of low-frequency charge...
Hole spin qubits can be implemented by accumulating holes in quantum dots (QDs) along the channel of a silicon fin field effect transistor (finFET). While the finFET design should lead to a field focusing at the tip of the fin, we frequently observe spurious hole accumulation under the gates outside the fin. To mitigate this problem, we implement a planar MOSFET platform including screening...
Quantum generative models have the potential to provide a quantum advantage, but their scalability is still in question. We investigate the barriers to training quantum generative models, focusing on exponential loss concentration. The interplay between explicit and implicit models and losses is explored, leading to untrainability of explicit losses (e.g., KL-divergence). Maximum Mean...
Hole spins in Ge/Si core/shell nanowires show a strong and electrically tunable spin-orbit (SO) interaction, allowing strong coupling between spins and photons. A highly tunable hole spin qubit was demonstrated using this system. However, the readout so far has relied on transport, so the qubit was not operated in the few-hole regime.
We present spectroscopy measurements on Ge/Si nanowire...
Holes in germanium/silicon core/shell nanowires are a powerful platform to study and optimize properties of spin qubits. This is a consequence of the strong, gate-tunable direct Rashba spin-orbit interaction, arising from strong confinement in the nanowire. So far, experiments in this system have been done in DC transport, preventing single-shot readout.
Here, we show gate-dispersive charge...
Rare-earth ions are promising qubit candidates for quantum information processing due to their narrow homogeneous linewidth and long coherence times. Within this family, erbium owns the feature of transition wavelengths at the telecom C-band, allowing for long-distance transmission. Here, in an Er$^{3+}$-doped solid-state system, we first introduce a scheme for implementing universal quantum...
Ultra-clean germanium/silicon (Ge/Si) core shell nanowires (NWs) have been predicted and proven to host highly stable hole spin qubits, controllable via Rashba spin orbit interaction with a large scalability potential making it possible to develop realistic and reliable quantum computers. To maximise their performance, high quality crystalline NWs grown along ⟨110⟩ direction with well-defined...
Microwave photonics is an innovative solution for radio frequency (RF) generation and distribution, by interconnecting the field between RF and photonics. Within the MICOR project, Menhir Photonics AG in collaboration with CSEM developed an ultra-low phase noise photonics-based RF source. The innovative RF generation not only generates ultra-low phase noise RF signals, but possesses the key...
We present a IPPL, a C++ framework for Particle-in-Cell methods based on dimension independent particles and fields. IPPL makes use of Kokkos and HeFFTe (part of the Exascale Computing Project), and MPI (Message Passing Interface) to obtain a massively parallel performance portable code which works across various hardware architectures. We showcase its performance and utility using "Alpine", a...
We illustrate an approach to study and design physics-consistent infinite neural networks for regression by falling back on stochastic Gaussian process theory. This mathematical connection allows to hard-code prior physics knowledge expressed in terms of linear (differential) operators directly into the model structure, in contrast to weak constraints with optimization regularization. Prime...
