A5063843765- Electronic and Structural Properties of Oxides
- Physics of Superconductivity and Magnetism
- Magnetic and transport properties of perovskites and related materials
- Surface and Thin Film Phenomena
- Quantum and electron transport phenomena
- Advanced Condensed Matter Physics
- Semiconductor materials and devices
- Topological Materials and Phenomena
- Graphene research and applications
- Magnetic properties of thin films
- Advanced Chemical Physics Studies
- Electron and X-Ray Spectroscopy Techniques
- Organic and Molecular Conductors Research
- 2D Materials and Applications
- Iron-based superconductors research
- Rare-earth and actinide compounds
- Inorganic Chemistry and Materials
- Magnetic Properties and Synthesis of Ferrites
- Ferroelectric and Piezoelectric Materials
- Molecular Junctions and Nanostructures
- Advanced Materials Characterization Techniques
- Catalytic Processes in Materials Science
- Iron oxide chemistry and applications
- X-ray Spectroscopy and Fluorescence Analysis
- Chalcogenide Semiconductor Thin Films
University of Würzburg
2016-2025
Complexity and Topology in Quantum Matter
2019-2023
Polish Academy of Sciences
2021
Institute of Fundamental Technological Research
2021
University of British Columbia
2011
Augsburg University
2001-2008
University of Augsburg
1999-2007
Goethe University Frankfurt
2007
Nagoya University
2004
Saarland University
1994-2001
Quantum spin Hall (QSH) materials promise revolutionary device applications based on dissipationless propagation of currents. They are two-dimensional (2D) representatives the family topological insulators, which exhibit conduction channels at their edges inherently protected against scattering. Initially predicted for graphene, and eventually realized in HgTe quantum wells, QSH systems so far, decisive bottleneck preventing is small bulk energy gap less than 30 meV, requiring cryogenic...
The conducting interface of ${\mathrm{LaAlO}}_{3}/{\mathrm{SrTiO}}_{3}$ heterostructures has been studied by hard x-ray photoelectron spectroscopy. From the Ti $2p$ signal and its angle dependence we derive that thickness electron gas is much smaller than probing depth 4 nm carrier densities vary with increasing number ${\mathrm{LaAlO}}_{3}$ overlayers. Our results point to an electronic reconstruction in overlayer as driving mechanism for corroborate recent interpretation superconducting...
Observations of the anomalous Hall effect in RuO2 and MnTe have demonstrated unconventional time-reversal symmetry breaking electronic structure a recently identified new class compensated collinear magnets, dubbed altermagnets. While MnTe, signal accompanied by vanishing magnetization is observable at remanence, excluded for Néel vector pointing along zero-field [001] easy-axis. Guided analysis ab initio calculations, field-induced reorientation from easy-axis toward [110] hard-axis was...
Abstract 2D topological insulators promise novel approaches towards electronic, spintronic, and quantum device applications. This is owing to unique features of their electronic band structure, in which bulk-boundary correspondences enforces the existence 1D spin–momentum locked metallic edge states—both helical chiral—surrounding an electrically insulating bulk. Forty years since first discoveries phases condensed matter, abstract concept topology has sprung into realization with several...
We have performed photoemission and inverse experiments on a series of 3d-transition-metal oxides with formal ionic configuration from to . The core-level spectra are analysed in terms simple cluster model leading estimates for the charge-transfer energy , Coulomb correlation hybridization strength V. It is found that ratio significantly decreases late early transition metal oxides. This trend attributed mostly increasing number empty d states metals which enhances effective metal-ligand...
The interface between LaAlO3 and SrTiO3 hosts a two-dimensional electron system of itinerant carriers, although both oxides are band insulators. Interface ferromagnetism coexisting with superconductivity has been found attributed to local moments. Experimentally, it established that Ti 3d electrons confined the interface. Using soft x-ray angle-resolved resonant photoelectron spectroscopy we have directly mapped states in k-space. Our data demonstrate charge dichotomy. A mobile fraction...
We report on the epitaxial fabrication and electronic properties of a topological phase in strained α-Sn InSb. The surface state forms presence an unusual band order not based direct spin-orbit coupling, as shown density functional GW slab-layer calculations. Angle-resolved photoemission including spin detection probes experimentally how spin-polarized emerges from second bulk valence band. Moreover, we demonstrate precise control Fermi level by dopants.
A new undulator beamline (P22) for hard X-ray photoelectron spectroscopy (HAXPES) was built at PETRA III (DESY, Hamburg) to meet the increasing demand HAXPES-based techniques. It provides four special instruments high-resolution studies of electronic and chemical structure functional nano-materials catalytic interfaces, with a focus on measurements under operando and/or ambient conditions: (i) versatile solid-state setup optional wide-angle lens in-situ electrical characterization, (ii)...
Upon reduction of the film thickness we observe a metal-insulator transition in epitaxially stabilized, spin-orbit-coupled SrIrO_{3} ultrathin films. By comparison experimental electronic dispersions with density functional theory at various levels complexity identify leading microscopic mechanisms, i.e., dimensionality-induced readjustment octahedral rotations, magnetism, and correlations. The astonishing resemblance band structure two-dimensional limit to that bulk Sr_{2}IrO_{4} opens new...
Atomic monolayers on semiconductor surfaces represent an emerging class of functional quantum materials in the two-dimensional limit - ranging from superconductors and Mott insulators to ferroelectrics spin Hall insulators. Indenene, a triangular monolayer indium with gap ~ 120 meV is insulator whose micron-scale epitaxial growth SiC(0001) makes it technologically relevant. However, its suitability for room-temperature spintronics challenged by instability topological character air. It...
Using x-ray photoelectron diffraction (XPD) and angle-resolved photoemission spectroscopy, we study intensity changes related to in the geometric electronic structure kagome metal CsV_{3}Sb_{5} upon transition an unconventional charge density wave (CDW) state. The XPD patterns reveal presence of a chiral atomic CDW phase. Furthermore, using circularly polarized x-rays, have found pronounced nontrivial circular dichroism angular distribution valence band phase, indicating chirality structure....
We present x-ray photoemission spectra of the vanadium oxides , and their analysis in terms a simple cluster model based on Anderson impurity Hamiltonian. The electronic structure these materials is characterized by strong V 3d-O 2p hybridization energy which exceeds scales related to on-site Coulomb correlation metal-ligand charge transfer. This result at variance with usual Mott-Hubbard picture, but agrees recent studies other early 3d transition metal compounds. ground-state occupations...
The electronic structure of the quasi-one-dimensional organic conductor TTF-TCNQ is studied by angle-resolved photoelectron spectroscopy (ARPES). experimental spectra reveal significant discrepancies to band theory. We demonstrate that measured dispersions can be consistently mapped onto one-dimensional Hubbard model at finite doping. This interpretation further supported a remarkable transfer spectral weight as function temperature. ARPES data thus show spectroscopic signatures spin-charge...
The electronic structure of high-Tc Bi2Sr2CaCu2O8 single crystals in the vicinity Fermi level EF is determined down to about 0.7Tc by high-resolution angle-resolved photoemission spectroscopy applying HeI and synchrotron radiation. Spectra taken with 18 eV photon energy at an emission angle 9° reveal a clear edge T > Tc. For < Tc intensity changes distinctly—at it decreases whereas increases 100 meV below EF—accompanied shift onset higher binding energy. These observations can be...
We have performed high-resolution angle-resolved photoemission spectroscopy (ARPES) on the layered compound 1-T-${\mathrm{TiTe}}_{2}$, whose low-energy properties are those of a normal metal, and analyzed experimental line shapes in terms Fermi-liquid self-energy. find excellent agreement between measured theoretical spectral weight distribution, while profiles expected for other models such as marginal Fermi liquid clearly fail to reproduce spectra. This demonstrates that ARPES able reflect...
Unique electronic properties of self-organized Au atom chains on Ge(001) in novel $c(8\ifmmode\times\else\texttimes\fi{}2)$ long-range order are revealed by scanning tunneling microscopy. Along the nanowires an exceptionally narrow conduction path exists which is virtually decoupled from substrate. It laterally confined to ultimate limit single dimension, and strictly separated its neighbors, as not previously reported. The resulting conductivity shows a dramatic inhomogeneity 2 orders...
Insulating SrTiO3 (STO) can host 2D electron systems (2DESs) on its surfaces, caused by oxygen defects. This study shows that the STO surface exhibits phase separation once 2DES is formed and relates this inhomogeneity to recently reported magnetic order at surfaces interfaces. The results open pathways exploit defects for engineering electronic properties of oxides.
The quantum spin Hall effect (QSHE) has formed the seed for contemporary research on topological states of matter. Since its discovery in HgTe/CdTe wells and InAs/GaSb heterostructures, all such systems have so far been suffering from extremely low operating temperatures, rendering any technological application out reach. We formulate a theoretical paradigm to accomplish high temperature QSHE monolayer-substrate heterostructures. Specifically, we explicate our proposal hexagonal compounds by...
The layered charge-density-wave (CDW) material $2H\ensuremath{-}{\mathrm{NbSe}}_{2}$ was studied by angle-resolved photoelectron spectroscopy. We present the first experimental mapping of Fermi surface (FS) portions involved in CDW transition. From this and additional data on conduction band dispersion near level we conclude that instability is driven FS nesting not saddle point singularities.
We study the electronic structure of quasi-one-dimensional organic conductor TTF-TCNQ by means density-functional band theory, Hubbard model calculations, and angle-resolved photoelectron spectroscopy (ARPES). The experimental spectra reveal significant quantitative qualitative discrepancies to theory. demonstrate that dispersive behavior as well temperature-dependence can be consistently explained finite-energy physics one-dimensional at metallic doping. description even made quantitative,...
Angle-resolved photoemission measurements for bulk single crystals of ${\mathrm{Nd}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ce}}_{\mathit{x}}$${\mathrm{CuO}}_{4\mathrm{\ensuremath{-}}\mathit{y}}$ with x=0.15 show that the spectral weight which builds in gap x=0 insulator displays a Luttinger Fermi surface, first such observation material is electron doped and must be driven metallic by alloying. This finding greatly strengthens our previous ocnclusion metal's chemical potential lies...
Temperature-dependent x-ray diffraction of the low-dimensional spin 1/2 quantum magnet TiOCl shows that phase transition at T_{c2} = 90 K corresponds to a lowering lattice symmetry. Below T_{c1} 66 twofold superstructure develops, indicates formation spin-singlet pairs via direct exchange between neighboring Ti atoms, while role superexchange is found be negligible. thus identified as spin-Peierls system pure 1D chains atoms. The first-order character explained by competition structurally...
Applying in situ combination of angle-resolved photoemission and inverse to cleaved III-V compound semiconductor (110) surfaces, we have determined the surface band gaps between filled anion-derived dangling-bound state ${\mathit{A}}_{5}$ empty cation-derived ${\mathit{C}}_{3}$ at \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{}, X\ifmmode\bar\else\textasciimacron\fi{} ', X\ifmmode\bar\else\textasciimacron\fi{}, M\ifmmode\bar\else\textasciimacron\fi{} points Brillouin zone. The...