Studies of topological strings is important both for condensed matter physics and cosmology, where they share the universality class with cosmic strings. Until recently these studies were bound to the surface phenomena or to destructive studies where layers of material were removed and imaged, thus preventing researchers to look into time-dependent behavior. We combined group-theoretical...
Beside the reduction of CO2 emissions by switching from fossil to renewable energy sources, alternative strategies to limit the greenhouse effect are represented by its storage and/or utilization. Among the various proposed utilization reactions, a potentially viable route is the direct CO2 fixation in organic carbonates, whose industrial interest as green chemicals is...
The knowledge of the elementary excitations is vital for understanding the physics of superconducting cuprates. Nowadays, Resonant Inelastic X-ray Scattering (RIXS) plays an increasingly important role in studying various excitations especially the spin excitations in cuprates. However, the interpretation of the measured excitations is still controversial. One obstacle is that the measured...
Lead-halide perovskite (LHP) semiconductors rival conventional semiconductors in multiple optoelectronic applications. The origin of such outstanding transport propeties are howerer not yet fully understood. We find signatures of large polaron formation in the electronic structure of the inorganic LHP CsPbBr$_3$ by means of angle-resolved photoelectron spectroscopy. The experimental valence...
(Mn,Ge)Te is a remarkable multiferroic material that combines ferroelasticity, ferroelectricity, ferromagnetism and a topological band structure [1,2]. The interplay of these effects via ferroelectric polarization and Rashba spin splitting makes it attractive for device applications in electronics, spintronics and quantum computing. Using photoelectron diffraction (XPD) in an operando setup...
Many important chemical and biological processes occur at the interface between a solid and a liquid, which is difficult to access for chemical analysis. The large inelastic scattering cross section of electrons in the condensed matter makes X-ray photoelectron spectroscopy (XPS) highly surface sensitive but less sensitive to buried interfaces. This limitation can be overcome by stabilizing an...
Weyl fermions as emergent quasiparticles can arise in Weyl semimetals (WSMs) in which the energy bands are nondegenerate, resulting from inversion or time-reversal symmetry breaking. Nevertheless, experimental evidence for magnetically induced WSMs is scarce. Here, using photoemission spectroscopy, we observe that the degeneracy of Bloch bands is already lifted in the paramagnetic phase of...
Cryo-cooled supercomputers and quantum computation are prospective directions of IT development, which both face the same barrier: No high-performance storage memory is available for low-temperature operation. A promising candidate for a future ultrafast memory device is the layered transition metal dichalcogenide 1T-TaS2, which has undergone a recent resurgence of interest with the discovery...
Thin film deposition is a technique useful in many scientific domains.
Our sputtering lab provides their coating services for all PSI groups, developing novel thin layers, lending support in sample preparation and manufacturing of instrument components.
The lab is equipped with 2 sputtering plants that have 3 target stations each and cover 50x200 mm^2 and 400 x 580 mm^2 respectively. ...
In this work, we present a systematic theoretical and experimental investigation of the use of Silicon Carbide thin (thicknesses between 500nm and 10µm) low-doped large area (>10mm2) membranes as X-ray sensors for beam position monitoring (XBPM) applications at synchrotron light sources (SLS).
Methane dehydroaromatisation reaction (MDA) is of increasing industrial interest to convert methane directly into benzene, valuable precursor for the chemical industry. Mo-containing zeolites are promising catalysts for MDA, Mo species activate methane while the zeolite pores provide shape selectivity to benzene; however, the rapid material deactivation due to carbon deposit accumulation...
The Dzyaloshinskii-Moriya interaction (DMI) is believed to be operative in low-symmetry crystal lattices lacking inversion symmetry. However, already in 1963, Arrott pointed out that even in a high symmetry lattice, where the DMI would normally vanish, this interaction is present in the vicinity of any lattice defect. Based on these considerations and recent theoretical work, first...
All optical switching (AOS) of the magnetization, discovered over a decade ago in GdFeCo ferrimagnetic alloy, is a hot topic in ultrafast condensed matter science due to high potential for implementation in data storage technology, substituting the writing head by ultrashort laser pulses in magnetic hard drives. However, most of study was on thin films, where the switched area is compatible...
As real devices necessarily contain defects, it is of interest to study wave propagation in disordered systems. In this work, we start from a 2D square lattice of magnetic spins with nearest-neighbour interactions and replace a fixed proportion of magnetic sites with nonmagnetic defects ('Site Percolation Model'). We are primarily interested in the disorder-averaged momentum signatures that...
Additive manufacturing (AM) processes allow the building of three-dimensional (3D) parts by progressively adding thin layers of materials guided by a digital model. AM processes are known for the complexity of the processing parameters which can greatly influence the materials properties such as porosity, residual stresses, microstructure and mechanical behavior.
Within the Neutron Imaging...
Photocatalysts and photoelectrodes play an important role to promote the decomposition of water to hydrogen (H2) and oxygen(O2). Various kinds of photocatalysts/photoelectrodes have been proposed for the last several decades. However, new materials are still explored to enhance its catalytic efficiency for our daily use. Fundamental studies on the mechanisms of...
The 2D electron gas (2DEG) formed at the surface of SrTiO$_3$(001) has attracted great interest because of its fascinating physical properties and promise as a novel electronic platform, but up to now has eluded a stable way to tune its properties. Using angle-resolved photoemission spectroscopy with and without spin resolution we here show that the band filling can be controlled by growing...
High penetration ability of neutrons and dramatic character of crystal structure modifications occurring in the battery materials during electrochemical cycling make neutron powder diffraction an obvious method to study the reaction mechanisms in rechargeable cells. While basic chemical reactions occurring in batteries upon charge/discharge are mainly understood, the specific processes leading...
Switchable molecules exhibiting tunable physical properties as a function of external stimuli (electric or magnetic fields, temperature, light or pressure) have drawn a considerable interest for their useful functionalities [1,2]. Nevertheless, with the considerable attraction for those systems, some fundamental and practical challenges arise in view of their integration in molecule-based...
Hydrogen (hydrides) distribution in the nuclear fuel claddings can often be highly non-uniform because of the high mobility of hydrogen interstitial atoms, raising the risk to the nuclear fuel rod integrity. High-resolution neutron imaging provides an excellent non-destructive tool for the quantification of the hydrogen in nuclear fuel claddings consisting of zirconium based alloys. The...
Copper is considered a possible candidate to replace precious metals in future three-way catalysts. Its performance as catalyst was assessed in operando conditions. A 20 wt% CuO/La$_{0.5}$Sr$_{0.5}$CoO$_3$ catalyst was studied under oscillating redox conditions while subjected to a temperature cycle 100$-$400$-$100$^o$C. Mass spectrometry was used to monitor gas compositions while...
We present our study of a magnetic structure in R1/3Sr2/3FeO3 (R = La, Pr, Nd) system, which is interesting because it has a metal-insulator (MI) transition concomitantly with the magnetic ordering. In our previous paper [1] we have shown that the neutron powder diffraction data can be equally well fitted by two different magnetic space groups, namely a canted helical model P3_221 and a...
Fe3Sn2 is a predicted type-II Weyl semimetal which orders ferromagnetically below TC= 646 K. It undergoes a spin reorientation transition (SRT) between 300K-100 K which together with recently shown coupling between its easy axis and the band structure paves the way of external control of its bulk properties. By probing anisotropic magnetoresistance, and bulk magnetization, we understand its...
Transition metal chalcogenides (TMCh), which exhibit a wide spectrum of novel physical phenomena, are of vital importance in fundamental research and in many fields for future technological applications including spintronics, topological electronics, Motttronics, etc. Metastable, monoclinic tungsten diselenide (2M-WS$_2$) is the TMCh family member. It has been identify as a Dirac...
Charge density waves (CDWs) comprise a class of collective phenomena that find their roots in the interplay of (i) a materials electron density and (ii) its underlying atomic lattice. In the prominent reference system TiSe¬2, numerous experimental and theoretical studies have looked at the emergence of the CDW phase – yet until today the microscopic mechanisms remain elusive.[1,2] Based on our...
Molecular magnetic materials are coordination compounds, in which metal ions are linked with each other via suitable ligands. These materials exhibit a tremendous variety in their dimensionality, electrical, optical and magnetic properties, giving rise, e.g., to the coexistence of ferromagnetic order and electrical conductivity in layered molecular materials [1], photoswitchable compounds [2],...
The metal-insulator transition in 5d transition metal oxide NaOsO3 which occurs concomitantly with antiferromagnetic order (TMIT=TN) has been proposed to be driven by Slater mechanism [1, 2] i.e. it is the onset of the antiferromagnetic order that drives the system into an insulating state [3]. However, there is no consensus and other mechanisms such as a Lifshitz transition have been proposed...
Rich phase diagram [1] of oxide heterostructures such as rare earth nickelates (RNiO3) allows to play with their properties. In antiferromagnetic $NdNiO_{3}$ it has been shown that thickness can influence the type of magnetic ordering [2]. It has been proposed that interface has a strong impact on NNO magnetism. By ARPES and XMCD measurements, it has been shown that 5 u.c. NNO on top of 15...
In atomic physics, interactions between single-particle state and multi-particle continuum leads to distinct ionization processes interfering with each other, leads to the so-called Fano resonance. Similar concepts have also been materialized in nanostructured systems, such as semiconducting quantum dots or frustrated magnets. The later shows renormalized energy levels of the single-particle...
The pressure induced superconductivity in Ga-II phase of elemental Gallium (the transition temperature $T_{\rm c}\simeq 6.45$ K) was studied experimentally by means of muon-spin rotation. Experiments reveal that Ga-II is the type-I superconductor with the zero temperature ther-modynamic critical field $B_{\rm c}(0)=64.07(1)$ mT. The analysis of $B_{\rm c}(T)$ data within the phenomenological...
Multiple blends of aluminum and transition metal powders are solidified via selective laser melting (SLM) to create precipitation-strengthened alloys. Previous work has demonstrated the ability to manufacture Ni-base and Ti-Al-Nb oxide-dispersion strengthened (ODS) parts via AM for energy applications (i.e. gas and steam turbines). Al-(Sc,Zr) powders are blended from elemental...
Strong correlations in intermetallic compounds containing f-electron elements give rise to a wide variety of ground states. Superconducting states found in heavy fermion materials are candidates for unconventional pairing with intertwined orders [1]. CeCoIn5 is an intriguing example among this class of materials, with a dx2-y2 order parameter. Superconductivity is Pauli limited and coexists...
This work is focused on in-situ and time-resolved tomography of multiphase systems. Specifically, transport of liquids and gases in porous structure are investigated. The applications include catalyst coating for air pollution control and pharmaceutical drugs impregnation. The evolution of the studied systems are followed by X-ray tomography in 3D with temporal resolution one second. Necessary...
Thanks to its CMOS compatibility and “near” direct bandgap, Germanium (Ge) has been for long in the race for the development of a fully Si-compatible light source, as an alternative to the traditional III-V-on-Si laser integration. The offset $\Delta$E = E($\Gamma$)-E(L) = 140 meV of Ge can be reduced by tensile strain and/or by alloying with Sn, increasing the radiative recombination...
Magnetic three-dimensional structures on the nanoscale possess static and dynamic properties not found in their ‘flat’ counterparts. The recent development of three-dimensional lithography and probing techniques (such as X-ray tomography) has enabled the experimental investigation of such structures. Concurrently, simulations need to be developed to gain detailed understanding of the...
Materials hosting Weyl nodes (a pair of linear crossings in the band-structure, similar to Dirac points) yield an enormous potential for applications since they enable massless electrons leading to fast transport properties. A ferromagnetic Weyl semimetal enables a tuning of the berry curvature by an external field. Bandstructure calculations promise the R AlGe family (R = La, Ce, Pr) [1]...
In heavy fermion superconductors, the strong interlocking of charge and spin degrees of freedom creates unconventional superconductivity in the vicinity of complex magnetic ground states - an ideal test bed to study quantum phase transitions. A special case for the coexistence of superconducting and magnetic order is the well-known Q-phase in CeCoIn5 [1] where the antiferromagnetism coexists...
Applying the Selective Laser Melting (SLM) technology to ceramics is challenging due to not understood mechanisms of interaction of the powder with laser light, high melting temperature and low thermal shock resistance. FUORCLAM (Fundamental Understanding of Oxide Refractory Ceramics and Laser Additive Manufacturing) is a project in collaboration between PSI, ETH and EMPA, which aims to...
Transport properties of a material like electric or heat conductivity are generally not the same in all directions. The direction dependence can be described by a tensor, the form of which depends on the point group of the material. The Peltier and Seebeck effects describe the interaction between thermal and electric transport properties. If a magnetic field is applied to the material,...
In the edge-shared spin-chain CuGeO3, the relation between charge, spin and lattice degrees of freedom, giving rise to the Spin-Peierls transition, is still unclear. In this regard, Resonant Inelastic X-ray Scattering (RIXS) represent a very powerful tool, capable of probing elementary excitations involving different degrees of freedom in a single experiment. Recently, the advent of...
Magnetic skyrmions are vortex-like topological spin textures often observed to form a triangular-lattice skyrmion crystal in structurally chiral magnets with the Dzyaloshinskii-Moriya interaction. Recently, beta-Mn structure–type Co-Zn-Mn alloys were identified as a new class of chiral magnet to host such skyrmion crystal phases, while beta-Mn itself is known as hosting an elemental...
In condensed matter, frustration emerges from the impossibility to satisfy all constraints simultaneously. Oft-times, this leads to exotic phases of matter with quasi-particle excitations. One such example is the Coulomb phase of spin ice which has emergent monopole excitations. The Coulomb phase has a highly degenerate ground state but with long-range correlation whose signature are the pinch...
Austenitic stainless steels, such as 304L, exhibit a combination of high strength and ductility and good corrosion resistance and due to their good selective laser melting (SLM) processability, they are ideal candidates for medical applications profiting e.g. from the possibility to manufacture complex geometries. In situ tensile and neutron diffraction tests on the POLDI instrument at the...
Materials with correlated structural disorder may be viewed as a different material class to conventional crystalline materials with either vanishingly small levels of disorder or, on the other hand, strong random disorder. Both spin and lattice dynamics of a frustrated magnets with an underlying correlated but disordered structure such as a charge ice can be unconventional. In this project,...
Frustrated magnets are a particularly promising class of materials for studying emergent phenomena in condensed matter. The construction of field theories describing the correlations and excitations of spins on a pyrochlore lattice is a prominent example. Such theories are typically based on a Coulomb phase, in which a non-divergent field with power-law correlations encodes the correlation...
The search of new classes of materials where superconductivity (SC) coexists with other exotic nonmagnetic phases is crucial to understand the influence of the latter on SC. Here, we present a detailed investigation of the superconducting gap symmetry on a charge-density-wave (CDW) superconductor SrPt2As2 by means of muon-spin rotation/relaxation technique (μSR) at ambient- and under...
Hydrogenation reactions occupy an important place in the realm of catalysis with various functional groups such as double and triple bonds and aldehydes among others which can undergo hydrogenation to produce diverse intermediates and fine chemicals [1]. In the fine chemical industry, these reactions are often performed in liquid phase due to the thermal stability and sensitivity of the...
Crystallization is often suppressed by point defects due to larger impurity particles. Surprisingly, microgels can overcome this limitation: Large microgels can spontaneously deswell to fit into the crystal lattice of smaller but otherwise identical microgels. We find this unique reduction of polydispersity and particle deswelling to be triggered by a difference in osmotic pressure, Π, between...
Frustrated triangular lattice antiferromagnets show a variety of exotic properties. Experimental observations in NiGa2S4 S=1 system [1] suggest i) presence of quadrupolar correlations [2] in addition to the moderate nearest-neighbor (J1) and strong third-neartest-neighbor (J3) Heisenberg interactions and ii) a topological transition driven by the Z2-vortex binding-unbinding [3].
We study the...
