Nodeless electron pairing in CsV3Sb5-derived kagome superconductors
The newly discovered kagome superconductors represent a promising platform for investigating the interplay between band topology, electronic order and lattice geometry. Despite extensive research efforts on this system, the nature of the superconducting ground state remains elusive. In particular, consensus on the electron pairing symmetry has not been achieved so far, in part owing to the lack of a momentum-resolved measurement of the superconducting gap structure. Here we report ...
Ultrafast structural changes direct the first molecular events of vision
The visual pigment rhodopsin plays a critical role in the process of low-light vision in vertebrates. It is present in the disk membranes of rod cells in the retina and is responsible for transforming the absorption of light into a physiological signal. Rhodopsin has a unique structure that consists of seven transmembrane (TM) α-helices with an 11-cis retinal chromophore covalently bound to the Lysine sidechain of 7th TM helix. A negatively charged amino acid (glutamate) forms a salt bridge with the protonated Schiff base (PSB) of the chromophore to stabilize the receptor in the resting state.
Rhodopsin transforms the absorption of light into a physiological signal through conformational changes that activate the intracellular G protein transducin—a member of the Gi/o/t family—initiating a signaling cascade, resulting in electrical impulses sent to the brain and ultimately leading to visual perception. Although previous studies have provided valuable insights into the mechanism of signal transduction in rhodopsin, methods that provide both a high spatial and temporal resolution are necessary to fully understand the activation mechanism at the atomic scale from femtoseconds to milliseconds. This study presents the first experimentally-derived picture of the rhodopsin activation mechanism at the atomic scale using time-resolved serial femtosecond crystallography in association with hybrid quantum mechanics/molecular mechanics (QM/MM) simulations. The results show that light-induced structural changes in rhodopsin occur on a timescale of hundreds of femtoseconds, and they reveal new details about the conformational changes that occur during activation.
Quantum disordered ground state in the triangular-lattice magnet NaRuO2
It has long been hoped that spin liquid states might be observed in materials that realize the triangular-lattice Hubbard model. However, weak spin–orbit coupling and other small perturbations often induce conventional spin freezing or magnetic ordering. Sufficiently strong spin–orbit coupling, however, can renormalize the electronic wavefunction and induce anisotropic exchange interactions that promote magnetic frustration.
Active learning-assisted neutron spectroscopy with log-Gaussian processes
Neutron scattering experiments at three-axes spectrometers (TAS) investigate magnetic and lattice excitations by measuring intensity distributions to understand the origins of materials properties. The high demand and limited availability of beam time for TAS experiments however raise the natural question whether we can improve their efficiency and make better use of the experimenter’s time.
SDU: Software for high throughput automated data collection at SLS MX
The Smart Digital User (SDU) software for unattended data collection has been deployed at the macromolecular crystallography beamlines at the Swiss Light Source.
Amyloid-polysaccharide interfacial coacervates as therapeutic materials
Coacervation via liquid-liquid phase separation provides an excellent oppor- tunity to address the challenges of designing nanostructured biomaterials with multiple functionalities. Protein-polysaccharide coacervates, in particular, offer an appealing strategy to target biomaterial scaffolds, but these systems suffer from the low mechanical and chemical stabilities of protein-based condensates. Here we overcome these limitations by transforming native proteins into amyloid fibrils and demonstrate ...
Mobility of Dissolved Gases in Smectite under Saturated Conditions
Mobility of water, sodium and gas molecules within a smectite nanopore
Various gases are produced by metal corrosion and organic material degradation in deep gelological repository for nuclear waste. To ensure repository safety, it's important to demonstrate that gases can be dissipated by diffusion in host rocks and prevent pressure buildup in repository near field. Smectite mineral particles form a pore network that is usually saturated with water, making gas diffusion the primary transport mechanism. Molecular simulations have shown that the diffusion of gases through the pore network depends on various factors, including pore size and temperature. For instance, smaller pores and lower temperatures tend to reduce gas diffusion. Interestingly, hydrogen and helium have been found to diffuse faster than argon, carbon dioxide, and methane, possibly due to interactions with the clay surface and water molecules. Ultimately, the diffusion coefficients for different gases and pore sizes can be predicted using an empirical relationship, which is useful for macroscopic simulations of gas transport.
The Hercules School visits PSI
20 international students visited PSI as part of the renowned Hercules School to learn about our state-of-the-art techniques and methodologies at our large scale facilities.
Latest Version of "Mobiltool" Released
How do you get from A to B in the most environmentally friendly way? This question can now be answered quite easily with the latest version of the "mobitool". Read the article to learn more.
Towards Next Generation Membranes for Polymer Electrolyte Water Electrolysis
The conversion efficiency for green hydrogen production in a polymer electrolyte water electrolyzer (PEWE) is strongly influenced by the ohmic cell resistance and therefore the thickness of the membrane. The use of thin membranes (~50 micron or below) is limited by gas crossover of H2 and O2, which can lead to the formation of an explosive gas mixture. The incorporation of a Pt recombination catalyst provides remedy and allows a more dynamic operating mode (cf. Highlight 03/2022). However, the presence of Pt nanoparticles leads to an increase in the rate of membrane degradation. Therefore, we have additionally doped the membrane with cerium-zirconium-oxide (CZO) nanoparticles, which act as radical scavenger. The rate of membrane degradation can thus be reduced.
Approximate Computing for Nuclear Reactor Simulations
During the last decades, computing power has been subject to tremendous progress due to the shrinking of transistor size as predicted by Moore’s law. However, as we approach the physical limits of this scaling, alternative techniques have to be deployed to increase computing performance. In this regard, the next big advance is envisioned to be the usage of approximate computing hardware based on field-programmable gate arrays and/or digital-analogue in-memory circuits. Such approximate computing can provide disproportional gain (x1000) in energy efficiency and/or execution time for acceptable loss of simulation accuracy. This could be highly beneficial in order to accelerate computational intensive simulations such as reactor core analyses with higher resolution multi-physics models. On the other hand, the execution of programming codes on low-precision hardware may result in inadequate outcomes due to quality degradation and/or algorithm divergence. To address these questions, studies on the stability and the performance of advanced reactor simulation algorithms as function of reduced floating-point arithmetic precision are being conducted at the laboratory for reactor physics and thermal-hydraulics. Results obtained so far indicate a large room for the acceleration of nuclear engineering applications using mixed-precision hardware. Therefore, research is now being enlarged towards assessing multiprecision computing methods for reactor core simulations with higher spatial resolution.
A practical guide to pulsed laser deposition
Nanoscale thin films are widely implemented across a plethora of technological and scientific areas, and form the basis for many advancements that have driven human progress, owing to the high degree of functional tunability based on the chemical composition. Pulsed laser deposition is one of the multiple physical vapour deposition routes to fabricate thin films, employing laser energy to eject material from a target in the form of a plasma ...
Activity Trend Origin of Ethanol Oxidative Dehydrogenation over VOx/CeO2
Using operando time-resolved X-ray absorption spectroscopy, we investigated the origin of volcano-shaped ethanol oxidative dehydrogenation activity trend of VOx/CeO2 catalysts as a function of VOx surface coverage. Vanadium and cerium synergistically change their oxidation states during the catalytic cycle. The catalytic activity correlates with the concentration of reversible Ce4+/3+species.
Integration of Li4Ti5O12 crystalline films on silicon towards high-rate performance lithionic devices
The growth of crystalline Li-based oxide thin films on silicon substrates is essential for the integration of next-generation solid-state lithionic and electronic devices. In this work, we employ a 2 nm γ-Al2O3 buffer layer on Si substrates in order to grow high quality crystalline thin films Li4Ti5O12 (LTO). Long-term galvanostatic cycling of 50 nm LTO demonstrates exceptional electrochemical performance, specific capacity of 175 mAh g-1 and 56 mAh g-1 at 100C and 5000C respectively, with a capacity retention of 91% after 5000 cycles.
Preparation, Quantification, and Reaction of Pd Hydrides on Pd/Al2O3 in Liquid Environment
The ability to study in situ the formation and consumption of Pd hydrides (PdH) in liquid environments is a significant challenge hampering a deeper understanding of catalyzed liquid-phase hydrogenation reactions. Here, using quick scanning X-ray absorption spectroscopy (QEXAFS), we present a detailed kinetic study of Pd hydride formation and reactivity on Pd/Al2O3 in 2-propanol solvent.
Momentum-resolved electronic structure of LaTiO2N photocatalysts by resonant Soft-X-ray ARPES
Oxynitrides are promising materials for visible light-driven water splitting. However, limited information regarding their electron-momentum resolved electronic structure exists. Here, with the advantage of the enhanced probing depth and chemical state specificity of soft-X-ray ARPES, we determine the electronic structure of the photocatalyst oxynitride LaTiO2N and monitor its evolution as a consequence of the oxygen evolution reaction. After the photoelectrochemical reactions, we observe a partial loss of Ti- and La-N 2p states, distortions surrounding the local environment of titanium atoms and, unexpectedly, an indication of an electron accumulation layer at or near the surface, which may be connected with either a large density of metallic surface states or downward band bending. The distortions and defects associated with the titanium 3d states lead to the trapping of electrons and charge recombination, which is a major limitation for the oxynitride LaTiO2N. The presence of an accumulation layer and its evolution suggests complex mechanisms of the photoelectrochemical reaction, especially in cases where co-catalysts or passivation layers are used.
Advancing the JUNGFRAU detector toward low-energy X-ray applications
“Soft” x-rays are notoriously hard to detect. Particularly, in the context of high-performance synchrotron and free electron laser (FEL) experiments, suitable detector options for low-energy x-rays are highly sought after. Currently available options only provide limited area, readout speed, and dynamic range. Now, a team of scientists from the Laboratory for X-Ray Nanoscience and Technologies (LXN) at PSI are challenging these limitations. They combined a detector made at PSI with newly developed silicon sensors to push the resolution toward the soft x-ray limit. A first version of this detector system is now in operation at the SwissFEL endstation Maloja. And it points to further possibilities to refine the detector technology to eventually catch the elusive soft x-rays.
Visualizing Higher-Fold Topology in Chiral Crystals
Novel topological phases of matter are fruitful platforms for the discovery of unconventional electromagnetic phenomena. Higher-fold topology is one example, where the low-energy description goes beyond standard model analogs. Despite intensive experimental studies, conclusive evidence remains elusive for the multigap topological nature of higher-fold chiral fermions. In this Letter, we leverage a combination of fine-tuned chemical engineering and photoemission spectroscopy with photon energy contrast to discover the higher-fold topology of a chiral crystal.
Spectroscopy vs. Electrochemistry: Catalyst Layer Thickness Effects on Operando/In Situ Measurements
Operando/in situ spectro-electrochemical studies often require high loadings and thick catalyst layers (CLs) leading to large ion- and mass-transport limitations. In this study we investigate PdH-formation in two Pd-catalysts with similar surface areas but drastically different morphologies. Our results unveil that the CL-thickness largely determines the PdH formation trends calling for the minimization of the CL-thickness in such experiments.
IEEE Early Career Award 2022
For contributions to the development of detectors for XFELs and specifically for their verification, characterization, and calibration
Commissioning of the novel Continuous Angle Multi-energy Analysis spectrometer at the Paul Scherrer Institut
We report on the commissioning results of the cold neutron multiplexing secondary spectrometer CAMEA (Continuous Angle Multi-Energy Analysis) at the Swiss Spallation Neutron Source at the Paul Scherrer Institut, Switzerland. CAMEA is optimized for ...
Simulations on "Piz Daint" explain surprising mineral behaviour
Zeolites are a class of shapely, colourful minerals with very special properties, making them omnipresent in our surroundings. They accelerate chemical reactions, absorb hazardous contaminants and water to a high degree, for example. Their only limitation is that they usually lose their peculiar crystalline structure at high temperatures. Now researchers at the University of Bern have found an unexpected exception.
Discovery of a large unquenched orbital moment in a 2D van der Waals ferromagnet
3d transition metals often exhibit a quenched orbital moment when in a solid state system. Therefore, the proposition of a large unquenched orbital moment for V in VI3 caused some surprise and discussion in the scientific community. Experimental and theoretical works diverge on the fact of whether the orbital moment is quenched or not. In our work we have been able to give an answer this open issue, proposing also a model for the ground state of VI3.
Updated electrochemical impedance model for understanding the interface of metallic lithium
Lithium metal negative electrodes are often used as counter electrodes while testing other electrochemically active materials, and are considered to be equivalent, independently of their thickness, supplier and production processes used. Here, we clearly demonstrate, using Electrochemical Impedance spectroscopy (EIS) that it is not the case, as well as the often-used symmetric cells are actually not so symmetric, when EIS spectra are disentangled using Thee-electrode cells.
CHART MagDev CCT Dipole achieves record field
As one of the first CHART projects, the MagDev activity at PSI designed and built a canted-cosine theta (CCT) demonstrator magnet, wound from Nb3Sn conductor.
Solidification modes during additive manufacturing
The thermal conditions during laser-based additive manufacturing are inferred from high-speed X-ray diffraction data and can be linked to a model for rapid solidification.
PLD plasma plume analysis, a summary of the PSI contribution
We report on the properties of laser-induced plasma plumes generated by ns pulsed excimer lasers as used for pulsed laser deposition to prepare thin oxide films. A focus is on the time and spatial evolution of chemical species in the plasma plume as well as the mechanisms related to the plume expansion. The overall dynamics of such a plume is governed by the species composition in particular if three or more elements are involved. We studied the temporal evolution of the plume, the composition of the chemical species in the plasma, as well as their electric charge. In particular, ionized species can have an important influence on film growth. Likewise, the different oxygen sources contributing to the overall oxygen content of an oxide film are presented and discussed. Important for the growth of oxide thin films is the compositional transfer of light element such as oxygen or Li. We will show and discuss how to monitor these light elements using plasma spectroscopy and plasma imaging and outline some consequences of our experimental results.
Fate of charge order in overdoped La-based cuprates
In high-temperature cuprate superconductors, stripe order refers broadly to a coupled spin and charge modulation with a commensuration of eight and four lattice units, respectively. How this stripe order evolves across optimal doping remains a controversial question. Here we present a systematic resonant inelastic x-ray scattering study of weak charge correlations in La2−xSrxCuO4 and La1.8−xEu0.2SrxCuO4. Ultra high energy resolution experiments demonstrate the importance of the separation of inelastic and elastic scattering processes. Long-range temperature-dependent stripe order is only found below optimal doping. At higher doping, short-range temperature-independent correlations are present up to the highest doping measured. This transformation is distinct from and preempts the pseudogap critical doping. We argue that the doping and temperature-independent short-range correlations originate from unresolved electron–phonon coupling that broadly peaks at the stripe ordering vector. In La2−xSrxCuO4, long-range static stripe order vanishes around optimal doping and we discuss both quantum critical and crossover scenarios.
Fate of charge order in overdoped La-based cuprates
In high-temperature cuprate superconductors, stripe order refers broadly to a coupled spin and charge modulation with a commensuration of eight and four lattice units, respectively. How this stripe order evolves across optimal doping remains a controversial question. Here we present a systematic resonant inelastic x-ray scattering study of weak charge correlations in La2−xSrxCuO4 and La1.8−xEu0.2SrxCuO4. Ultra high energy resolution experiments demonstrate the importance of the separation of inelastic and elastic scattering processes.
Unusual ferrimagnetism in CaFe2O4
Rare ferrimagnet states in a phase competing antiferromagnet.
Prevention of freezing propagation in fuel cells using segmentation
The ability to start-up in extreme environmental conditions, including sub-freezing temperatures, is essential to the deployment of the fuel cell technology. Water produced in fuel cells at these temperatures can be in the super-cooled state, and freezing can lead to a rapid shutdown, as water cannot be removed anymore as a liquid. By segmenting a fuel cell, it is possible to prevent the propagation of freezing, which enables the cell operation even after the first freezing event occurred.
Topological magnetic structures in MnGe: Neutron diffraction and symmetry analysis
From new neutron powder diffraction experiments on the chiral cubic (P213) magnet manganese germanide (MnGe), we analyze all of the possible crystal symmetry-allowed magnetic superstructures that are determined successfully from the data. The incommensurate propagation vectors k of the magnetic structure are found to be aligned with the [100] cubic axes, and correspond to a magnetic periodicity of about 30 Å at 1.8 K. Several maximal crystallographic symmetry magnetic structures are found to fit the data equally well and are presented. These include topologically nontrivial magnetic hedgehog and “skyrmion” structures in multi-k cubic or orthorhombic 3+3 and orthorhombic 3+2 dimensional magnetic superspace groups respectively, with either potentially responsible for topological Hall effect. The presence of orthorhombic distortions in the space group P212121 caused by the transition to the magnetically ordered state does not favor the cubic magnetic hedgehog structure, and leave both orthorhombic hedgehog and skyrmion models as equal candidates for the magnetic structures. We also report on a combined mechanochemical and solid-state chemical route to synthesize MnGe at ambient pressures and moderate temperatures, and compare with samples obtained by the traditional high pressure synthesis.
From light-years to nanometers: reconstruction of unknown oscillations in STXM
From light-years to nanometers: by repurposing an algorithm originally developed for the investigation of oscillatory dynamics in astronomical objects, scientists have been able to image non-locked dynamical processes at the nanosecond and nanometer scale.
Magnetic structure of R1/3Sr2/3FeO (R = Pr, Nd)
We present magnetization and neutron powder diffraction studies in the temperature range 2K to 300K for oxygen stoichiometric R1/3Sr2/3FeO (R = Pr and Nd). From full symmetry analysis, we proposed two magnetic models by a combined application of irreducible representations and magnetic space groups. Both models fit equally well the neutron powder diffraction data.
Manuel Guizar-Sicairos appointed as Associate Professor at EPF Lausanne and head of the Computational X-ray Imaging group at PSI
Dr. Manuel Guizar-Sicairos, currently Senior Scientist at PSI, was appointed as Associate Professor of Physics in EPF Lausanne and head of the Computational X-ray Imaging group in PSI.
Tracking chemical bond changes with element selectivity and in real time
X-ray photoelectron spectroscopy probes the chemical environment in a molecule at a specific atomic site. Now the concept is extended with a site selective trigger to follow chemical bond changes as they occur on the femtosecond time scale.
Evaluation of European electricity supply resilience
The increasing risk of extended electricity supply disruptions and severe electricity price fluctuations strongly motivate an evaluation of electricity supply resilience. In this direction, this research proposes a multicriteria decision support framework to assess resilience at a country level, based on three major dimensions: Resist, Restabilize and Recover. In total, 35 European countries are ranked according to their performance on 17 indicators, through a synergy of MCDA methods, techniques and communication protocols. The assessment framework has been extended to incorporate the Choquet Integral method, in order to accommodate potentially interacting pairs of criteria and negate their arbitrary effects on the final evaluation results. The analysis incorporates country data from credible international databases, as well as the preference information of a European energy expert. The results are envisaged to support energy policymakers in Europe and provide guidelines and areas for improvement at a country level.
Magnetic and crystal structure of the antiferromagnetic skyrmion candidate GdSb0.71Te1.22
GdSb0.46Te1.48, a nonsymmorphic Dirac semimetal with Dirac nodes at the Fermi level, has a rich magnetic phase diagram with one of the phases predicted to be an antiferromagnetic skyrmion state. In the current work, we investigate GdSb0.71Te1.22 through bulk magnetization measurements, single-crystal, and powder synchrotron X-ray diffraction, as well as single-crystal hot-neutron diffraction. We resolve a weak orthorhombic distortion with respect to the tetragonal structure and charge density wave (CDW) satellites due to incommensurate modulations of the crystal structure. At 2 K the magnetic structure is modulated with two propagation vectors, kI = (0.45 0 0.45) and kII = (0.4 0 0), with all their arms visible. While kI persists up to the transition to the paramagnetic state at TN = 11.9 K, kII disappears above an intermediate magnetic transition at T1 = 5 K. Whereas magnetic field applied along the c-axis has only a weak effect on the intensity of antiferromagnetic reflections, it is effective in inducing an additional ferromagnetic component on Gd atoms. We refine possible magnetic structures of GdSb0.71Te1.22 and discuss the possibility of hosting magnetic textures with non-trivial 3D+ 2 topologies in the GdSb1−xTe1+x series.
Thermal cycling during 3D laser printing
High-speed in situ X-ray diffraction is used to measure temperature profiles and cooling rates during 3D printing of a a Ti-6Al-4V single-track wall.
A unique environment for research on highly radioactive materials
PSI has a unique (worldwide) environment for the investigation of highly radioactive / toxic materials:
> Materials (different fuel types, very high burn-up, different cladding materials, materials activated in SINQ).
> The hot lab with advanced tools for microsample analysis and preparation.
> The large-scale equipment for advanced material analysis.
This unique combination at PSI allows us to meet the needs of our industrial partners to improve plant safety / efficiency, up to fundamental research.
The quantitative distribution of fission products over the cross-section of a pellet with a shielded electron probe microanalyzer (EPMA) used for verification analysis of the material behavior to validate the model. In this context, Xe behavior during transients/failure (LOCA, RIA) is an important safety parameter that can’t be measured with the EPMA at the periphery. Microstructural EBSD investigations on a microsample extend the information horizon, which is deepened at the microXAS beamline by detailed X-ray analyses.
Versatile and Fast Methodology for Evaluation of Metallic Lithium Negative Battery Electrodes
Evaluating potential electrolyte candidates is typically a lengthy procedure requiring long-term cycling experiments. To speed this process up, we have investigated potentiostatic lithium plating as a potential method for fast electrolyte suitability investigation. The applications of this methodology is not limited to liquid electrolytes, - effects of solid-state electrolytes, coatings, and other modifications can be readily assessed.
Consortium led by LMS wins funding to establish ORD practices
A consortium led by Dr. Giovanni Pizzi, Group leader of the “Materials Software and Data” group in the Laboratory for Materials Simulations, has won funding of almost CHF1.3 million for a three-year project dubbed PREMISE: “Open and reproducible materials science research.”
Single-domain stripe order in a high-temperature superconductor
The coupling of spin, charge and lattice degrees of freedom results in the emergence of novel states of matter across many classes of strongly correlated electron materials. A model example is unconventional superconductivity, which is widely believed to arise from the coupling of electrons via spin excitations. In cuprate high-temperature superconductors, the interplay of charge and spin degrees of freedom is also reflected in a zoo of charge and spin- density wave orders that are intertwined with superconductivity ...
Dancing molecules
When cycloalkanes are enclosed in a nanometer-sized pore, they adapt their shape - similar to the induced fit concept described in #biochemistry. The molecules do not all behave in the same way and surprisingly start to move when there is a lack of space at 5K.
Perspective on muon-spin rotation/relaxation under hydrostatic pressure
Pressure, together with temperature, electric, and magnetic fields, alters the system and allows for the investigation of the fundamental prop- erties of matter. Under applied pressure, the interatomic distances shrink, which modifies the interactions between atoms and may lead to the appearance of new (sometimes exotic) physical properties, such as pressure-induced phase transitions; quantum critical points; new structural, magnetic, and/or superconducting states; and changes of the temperature evolution and symmetry of the order parameters...
Platinum-Iron(II) Oxide Sites Directly Responsible for Preferential Carbon Monoxide Oxidation at Ambient Temperature: An Operando X-ray Absorption Spectroscopy Study
Operando X-ray absorption spectroscopy revealed a linear correlation between the amount of oxidic Fe2+ and the ambient temperature activity of Pt−FeOx preferential carbon monoxide oxidation catalysts. The hydrogen prereduction temperature and pressure determines the amount of active Fe2+ sites for alumina- and silica-supported Pt−Fe catalysts. Catalyst deactivation is linked with the oxidation of these sites.
Automated synapse-level reconstruction of neural circuits in the larval zebrafish brain
Researchers from the Max Planck Institute for Biological Intelligence, Google Inc. and the Paul Scherrer Institute published a new method and data resource that makes connectomic analyses of the entire larval zebrafish brain possible.
Li-ion solvation in TFSI and FSI - based ionic liquid electrolytes probed by X-ray photoelectron spectroscopy
We demonstrate the capability of conventional laboratory XPS to determine the anions solvation shell of Li+ cation within 1M of LiTFSI and 1M of LiFSI salts dissolved in (EMIM+-FSI-) and (EMIM+-TFSI-) ionic liquids. The binding energy difference between the N1s components originating from the EMIM+ cation and from TFSI- or FSI- anions, solvating the Li+, confirms that both TFSI- and FSI- contribute simultaneously to the Li+ solvation. Additionally, the degradation of the TFSI and FSI -based electrolytes under X-ray exposure is proved.