A5049583934- Electronic and Structural Properties of Oxides
- Magnetic and transport properties of perovskites and related materials
- Advanced Condensed Matter Physics
- Semiconductor materials and devices
- Physics of Superconductivity and Magnetism
- Organic and Molecular Conductors Research
- Magnetic Properties and Synthesis of Ferrites
- Ferroelectric and Piezoelectric Materials
- Quantum and electron transport phenomena
- Electron and X-Ray Spectroscopy Techniques
- Molecular Junctions and Nanostructures
- Iron oxide chemistry and applications
- Catalytic Processes in Materials Science
- Magnetic properties of thin films
- Advanced Chemical Physics Studies
- Multiferroics and related materials
- Inorganic Chemistry and Materials
- Fullerene Chemistry and Applications
- High-pressure geophysics and materials
- Surface and Thin Film Phenomena
- Graphene research and applications
- Advanced Materials Characterization Techniques
- Iron-based superconductors research
- Magnetism in coordination complexes
- Rare-earth and actinide compounds
University of Würzburg
2015-2024
Complexity and Topology in Quantum Matter
2019-2023
University of Newcastle Australia
2022-2023
University of British Columbia
2011
University of Augsburg
2001-2006
Augsburg University
2005
Osaka University
2004-2005
Seoul National University
2004
Leibniz Institute for Neurobiology
1998-1999
University of Sussex
1999
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...
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...
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...
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....
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...
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.
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,...
We report the formation of a nonmagnetic band insulator at isopolar interface between antiferromagnetic Mott-Hubbard ${\mathrm{LaTiO}}_{3}$ and charge transfer ${\mathrm{LaFeO}}_{3}$. By density-functional theory calculations, we find that this state is driven by combination O alignment crystal field splitting energy ${t}_{2g}$ ${e}_{g}$ bands. As result these two driving forces, Fe $3d$ bands rearrange electrons are transferred from Ti to Fe. This picture supported x-ray photoelectron...
Potassium-doped picene (K(x)picene) has recently been reported to be a superconductor at x=3 with critical temperatures up 18 K. Here we study the electronic structure of K-doped films by photoelectron spectroscopy and ab initio density functional theory combined dynamical mean-field (DFT+DMFT). Experimentally observe that, except for spurious spectral weight due lack homogeneous chemical potential low K concentrations (x≈1), spectra always display finite energy gap. This result is supported...
Abstract The Mott transistor is a paradigm for new class of electronic devices—often referred to by the term Mottronics—which are based on charge correlations between electrons. Since correlation‐induced insulating phases most oxide compounds usually very robust, methods have be developed push such materials right boundary metallic phase in order enable metal–insulator transition switched electric gating. Here, it demonstrated that thin films prototypical insulator LaTiO 3 grown pulsed laser...
We present a detailed study of the electronic structure and band alignment in LaAlO${}_{3}$/SrTiO${}_{3}$ oxide heterostructures by hard x-ray photoelectron spectroscopy. Our spectroscopic measurements find no evidence for strong potential gradient within polar LaAlO${}_{3}$ film predicted theory. Due to high interface sensitivity method, we are further able determine valence offset between SrTiO${}_{3}$ substrate, which is found be independent number LAO overlayers. Finally, discuss several...
The high-energy spectroscopic study of the electronic structure fullerenes and their compounds in solid state is reviewed. It shown that photoemission electron energy-loss spectroscopy transmission provide powerful tools for experimental C60, C70 higher fullerenes, as well formed by intercalation with alkali alkaline-earth metals. Topical issues field are addressed, such role played correlation, disorder electron-phonon coupling.
We report the Fermi surfaces of superconductor ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ and nonsuperconductor ${\mathrm{Sr}}_{1.8}{\mathrm{Ca}}_{0.2}{\mathrm{RuO}}_{4}$ probed by bulk-sensitive high-energy angle-resolved photoemission. It is found that there one square-shaped hole-like, electron-like, circle-shaped electron-like surface in both compounds. These results provide direct evidence for nesting instability giving rise to magnetic fluctuations. Our study clarifies electron correlation...
The microscopic origin of the two-dimensional electron system (2DES) at ${\mathrm{LaAlO}}_{3}/{\mathrm{SrTiO}}_{3}$ heterointerface remains a topic debate. Among others, mechanisms involving surface defects acting as donors for 2DES have been proposed recently. Since samples are usually investigated after exposure to air, adsorbates plausible candidate such defects. We therefore used in situ photoelectron spectroscopy and resistivity measurements study impact on 2DES. adsorbate coverage...
The complex conductivity at the (Verwey) metal-insulator transition in ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ has been investigated terahertz and infrared frequencies. In insulating state, both dynamic dielectric constant reveal a power-law frequency dependence, characteristic feature of hopping conduction localized charge carriers. process is limited to low frequencies only, cutoff ${\ensuremath{\nu}}_{1}\ensuremath{\simeq}8\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ must be introduced for...
Hard x-ray photoelectron spectroscopy (HAXPES) is a new variant of the well-established photoemission technique, which extends its range to much higher energies up 10 keV and thus enhanced probing depths order nm beyond. This not only facilitates direct access intrinsic bulk electronic structure solids, but also allows extended depth profiling study buried interfaces possible by conventional photoemission. Here, we present two HAXPES case studies on transition metal hybrid heterostructures...
More than a decade after the discovery of two-dimensional electron system (2DES) at interface between band insulators ${\mathrm{LaAlO}}_{3}$ (LAO) and ${\mathrm{SrTiO}}_{3}$ (STO) its microscopic origin is still under debate. Several explanations have been proposed, main contenders being doping by oxygen vacancies electronic reconstruction, i.e., redistribution electrons to minimize electrostatic energy in polar LAO film. However, no experiment thus far could provide unambiguous information...
The spinel/perovskite heterointerface $\gamma$-Al$_2$O$_3$/SrTiO$_3$ hosts a two-dimensional electron system (2DES) with mobilities exceeding those in its all-perovskite counterpart LaAlO$_3$/SrTiO$_3$ by more than an order of magnitude despite the abundance oxygen vacancies which act as donors well scattering sites. By means resonant soft x-ray photoemission spectroscopy and \textit{ab initio} calculations we reveal presence sharply localized type at very interface due to local breaking...
We present a comprehensive study of the band bending and alignment at interface $\ensuremath{\gamma}\text{\ensuremath{-}}{\text{Al}}_{2}{\text{O}}_{3}/{\text{SrTiO}}_{3}$ heterostructures by hard x-ray photoelectron spectroscopy. Our measurements find no signs for potential gradient within polar $\ensuremath{\gamma}\text{\ensuremath{-}}{\text{Al}}_{2}{\text{O}}_{3}$ film as predicted basic electronic reconstruction scenario. evidence on ${\text{SrTiO}}_{3}$ side interface, yielding roughly...
Low-temperature electronic properties of the charge-density-wave system NbSe3 are reported from angle-resolved photoemission at 15 K. The effect two instabilities q(1) and q(2) on k-resolved spectral function is observed for first time. With a pseudogap background, gap spectra exhibit maxima Delta*(1) approximately 110 meV Delta*(2) 45 meV. Imperfectly nested sections Fermi surface lack Fermi-Dirac edge, show signature dispersion that modified by self-energy effects. energy scale order...
We report the application of resonant inelastic x-ray scattering to explore nature single conducting interface in oxide heterostructure ${\text{LaAlO}}_{3}/{\text{SrTiO}}_{3}$. From $\text{Ti}\text{ }3d$ crystal-field excitations measured at }{L}_{3}$ resonance we not only derive information on local geometry but are also able follow evolution sheet carrier density with thickness ${\text{LaAlO}}_{3}$ overlayer. These findings confirm after calibration previous hard photoelectron spectroscopy...
We have studied the electronic structure and charge ordering (Verwey) transition of magnetite (Fe3O4) by soft X-ray photoemission. Due to enhanced probing depth use different surface preparations we are able distinguish volume effects in spectra. The pseudogap behavior intrinsic spectra its temperature dependence give evidence for existence strongly bound small polarons consistent with both dc optical conductivity. Together other recent structural theoretical results our findings support a...