A5014195398- Electronic and Structural Properties of Oxides
- Advanced Condensed Matter Physics
- Topological Materials and Phenomena
- Magnetic and transport properties of perovskites and related materials
- Physics of Superconductivity and Magnetism
- Electron and X-Ray Spectroscopy Techniques
- Iron-based superconductors research
- 2D Materials and Applications
- X-ray Spectroscopy and Fluorescence Analysis
- Graphene research and applications
- Semiconductor materials and devices
- Magnetic properties of thin films
- Rare-earth and actinide compounds
- Advanced Chemical Physics Studies
- Surface and Thin Film Phenomena
- Ga2O3 and related materials
- ZnO doping and properties
- Quantum and electron transport phenomena
- High-pressure geophysics and materials
- Crystallography and Radiation Phenomena
- X-ray Diffraction in Crystallography
- Chalcogenide Semiconductor Thin Films
- Magnetic Properties of Alloys
- Advanced Semiconductor Detectors and Materials
- Multiferroics and related materials
Paul Scherrer Institute
2016-2025
Swiss Light Source
2016-2025
University of California, Santa Barbara
2023
ORCID
2021
The University of Tokyo
2012-2014
University of Augsburg
2001-2004
Chalmers University of Technology
1995-2002
Centre National de la Recherche Scientifique
2000-2001
Institut de Neurobiologie de la Méditerranée
2000
Saarland University
1998-1999
Weyl semimetals are expected to open up new horizons in physics and materials science because they provide the first realization of fermions exhibit protected Fermi arc surface states. However, had been found be extremely rare nature. Recently, a family compounds, consisting tantalum arsenide, phosphide (TaP), niobium phosphide, was predicted as semimetal candidates. We experimentally realize state TaP. Using photoemission spectroscopy, we directly observe fermion cones nodes bulk, arcs on...
The concepts and technical realisation of the high-resolution soft X-ray beamline ADRESS operating in energy range from 300 to 1600 eV intended for resonant inelastic scattering (RIXS) angle-resolved photoelectron spectroscopy (ARPES) are described. photon source is an undulator novel fixed-gap design where longitudinal movement permanent magnetic arrays controls not only light polarization (including circular 0-180 degrees rotatable linear polarizations) but also without changing gap....
Abstract A Weyl semimetal possesses spin-polarized band-crossings, called nodes, connected by topological surface arcs. The low-energy excitations near the crossing points behave same as massless fermions, leading to exotic properties like chiral anomaly. To have transport dominated nodes need locate nearly at chemical potential and enclosed pairs of individual Fermi surfaces with non-zero Chern numbers. Combining angle-resolved photoemission spectroscopy first-principles calculation, here...
Abstract The metal–insulator transition and the intriguing physical properties of rare-earth perovskite nickelates have attracted considerable attention in recent years. Nonetheless, a complete understanding these materials remains elusive. Here we combine X-ray absorption resonant inelastic scattering (RIXS) spectroscopies to resolve important aspects complex electronic structure nickelates, taking NdNiO 3 thin film as representative example. unusual coexistence bound continuum excitations...
In quantum field theory, Weyl fermions are relativistic particles that travel at the speed of light and strictly obey celebrated Lorentz symmetry. Their low-energy condensed matter analogs semimetals, which conductors whose electronic excitations mimic fermion equation motion. Although traditional (type I) emergent observed in TaAs still approximately respect symmetry, recently, so-called type II semimetal has been proposed, where quasiparticles break symmetry so strongly they cannot be...
Lifted Kramers spin degeneracy (LKSD) has been among the central topics of condensed-matter physics since dawn band theory solids
Topological semimetals are characterized by symmetry-protected band crossings, which can be preserved in different dimensions momentum space, forming zero-dimensional nodal points, one-dimensional lines, or even two-dimensional surfaces. Materials harboring points and lines have been experimentally verified, whereas experimental evidence of surfaces is still lacking. Here, using angle-resolved photoemission spectroscopy (ARPES), we reveal the coexistence Dirac bulk electronic structures...
Topological semimetals feature protected nodal band degeneracies characterized by a topological invariant known as the Chern number (C). Nodal crossings with linear dispersion are expected to have at most |C|=4, which sets an upper limit magnitude of many phenomena in these materials. Here we show that chiral crystal PdGa displays multifold crossings, connected exactly four surface Fermi-arcs, thus proving they carry maximal 4. By comparing two enantiomers, observe reversal their Fermi-arc...
We present a 5m long spectrometer for soft x rays to be used at synchrotron radiation beamline resonant x-ray emission spectroscopy and inelastic scattering in the 400–1600eV energy range. It is based on variable line spacing spherical grating (average groove density of 3200mm−1, R=58.55m) charge coupled device two dimensional detector. With an spot sample 10μm, targeted resolving power higher than 10 000 all energies below 1100eV better 7000 1500eV. The off-line tests made with Al MgKα1,2...
We probe the collective magnetic modes of La2CuO4 and underdoped La2-xSrxCuO4 (LSCO) by momentum resolved resonant inelastic x-ray scattering (RIXS) at Cu L3 edge. For undoped antiferromagnetic sample, we show that single magnon dispersion measured with RIXS coincides one determined neutron scattering, thus demonstrating x rays are an alternative to neutrons in this field. In spin dynamics LSCO, find a branch dispersing up approximately 400 meV coexisting lower energy. The high-energy has...
The resolution of angle-resolved photoelectron spectroscopy (ARPES) in three-dimensional (3D) momentum k is fundamentally limited by ill defined surface-perpendicular wave vector k(perpendicular) associated with the finite mean free path. Pushing ARPES into soft-x-ray energy region sharpens definition, allowing accurate electronic structure investigations 3D materials. We apply to explore electron realm a paradigm transition metal dichalcogenide VSe2. Essential break through dramatic loss...
Soft-X-ray angle-resolved photoelectron spectroscopy (ARPES) with photon energies around 1 keV combines the momentum space resolution increasing probing depth. The concepts and technical realisation of new soft-X-ray ARPES endstation at ADRESS beamline SLS are described. experimental geometry is characterized by grazing X-ray incidence on sample to increase photoyield vertical orientation measurement plane. vacuum chambers adopt a radial layout allowing most efficient transfer. High accuracy...
Interplay of spin, charge, orbital and lattice degrees freedom in oxide heterostructures results a plethora fascinating properties, which can be exploited new generations electronic devices with enhanced functionalities. The paradigm example is the interface between two band insulators LaAlO3 SrTiO3 (LAO/STO) that hosts two-dimensional electron system (2DES). Apart from mobile charge carriers, this exhibits range intriguing properties such as field effect, superconductivity ferromagnetism,...
BiTeI has a layered and non-centrosymmetric structure where strong spin-orbit interaction leads to giant spin splitting in the bulk bands. Here we present high-resolution angle-resolved photoemission (ARPES) data UV soft x-ray regime that clearly disentangle surface from electronic structure. Spin-resolved UV-ARPES measurements on opposite, non-equivalent surfaces show identical structures, thus clarifying state character. Soft ARPES reveal spindle-torus shape of Fermi surface, induced by...
Inelastic x-ray scattering spectra excited at the 1s(-1)π* resonance of gas phase O2 have been recorded with an overall energy resolution that allows for well-resolved vibrational progressions. The nuclear wave packet dynamics in intermediate state is reflected excitations electronic ground state, and by fine-tuning excitation dissociation predissociative B'(3)Πg final controlled.
The complex electronic properties of ${\mathrm{ZrTe}}_{5}$ have recently stimulated in-depth investigations that assigned this material to either a topological insulator or 3D Dirac semimetal phase. Here we report comprehensive experimental and theoretical study both structural ${\mathrm{ZrTe}}_{5}$, revealing the bulk is strong (STI). By means angle-resolved photoelectron spectroscopy, identify at top valence band surface state. dispersion these bands well captured by ab initio calculations...
The Paul Scherrer Institute is planning the construction of a hardx-ray free-electron laser, SwissFEL, by 2016, which will produce intense, ultrashort pulses transversely coherent radiation in wavelength range 0.1-7 nm, with future extensions to cover 0.08-30 nm.Special design considerations include (a) compact construction, compatible status national facility, (b) uniform 100 Hz repetition rate, well suited sample manipulations and detector readout, (c) flexible tuning electron beam energy...
Amorphous materials represent a large and important emerging area of material’s science. oxides are key technological in applications such as gate dielectric Complementary metal-oxide semiconductor devices Silicon-Oxide-Nitride-Oxide-Silicon TANOS (TaN-Al 2 O 3 -Si N 4 -SiO -Silicon) flash memories. These technologies required for the high packing density today’s integrated circuits. Therefore investigation defect states these structures is crucial. In this work we present X-ray synchrotron...