A5067860643- Magnetic properties of thin films
- Topological Materials and Phenomena
- Quantum and electron transport phenomena
- Advanced Chemical Physics Studies
- Physics of Superconductivity and Magnetism
- Advanced Condensed Matter Physics
- Surface and Thin Film Phenomena
- Graphene research and applications
- Magnetic and transport properties of perovskites and related materials
- Electronic and Structural Properties of Oxides
- Multiferroics and related materials
- 2D Materials and Applications
- Electron and X-Ray Spectroscopy Techniques
- Laser-Matter Interactions and Applications
- Quantum many-body systems
- Theoretical and Computational Physics
- Advanced Electron Microscopy Techniques and Applications
- ZnO doping and properties
- Molecular Junctions and Nanostructures
- Quantum, superfluid, helium dynamics
- Atomic and Molecular Physics
- Phase-change materials and chalcogenides
- Quantum optics and atomic interactions
- Semiconductor materials and devices
- Optical Coatings and Gratings
Martin Luther University Halle-Wittenberg
2016-2025
Max Planck Institute of Microstructure Physics
2001-2012
Max Planck Society
2001-2011
Uppsala University
1997-1999
University of Duisburg-Essen
1994-1997
Surface alloying is shown to produce electronic states with a very large spin-splitting. We discuss the long range ordered bismuth/silver(111) surface alloy where an energy bands separation of up one eV achieved. Such strong spin-splitting enables angular resolved photoemission spectroscopy directly observe region close band edge, density shows quasi-one dimensional behavior. The associated singularity in local has been measured by low temperature scanning tunneling spectroscopy....
For magnons, the Dzyaloshinskii-Moriya interaction accounts for spin-orbit and causes a nontrivial topology that allows topological magnon insulators. In this theoretical investigation we present bulk-boundary correspondence magnonic kagome lattices by studying edge magnons calculated Green function renormalization technique. Our analysis explains sign of transverse thermal conductivity Hall effect in terms modes their propagation direction. The hybridization topologically trivial with...
Ferromagnetic insulators with Dzyaloshinskii-Moriya interaction show the magnon Hall effect, i.e., a transverse heat current upon application of temperature gradient. In this theoretical investigation we establish close connection effect in two-dimensional kagome lattices topology their dispersion relation. From topological phase diagram predict systems which change sign dependence on temperature. Furthermore, derive high-temperature limit thermal conductivity; quantity provides figure merit...
A magnetic bimeron is a pair of two merons and can be understood as the in-plane magnetized version skyrmion. Here we theoretically predict existence single bimerons well crystals, compare emergent electrodynamics with their skyrmion analogues. We show that crystals stabilized in frustrated magnets analyze what crystal structure stabilize or via Dzyaloshinskii-Moriya interaction. point out contrast to allow for detection pure topological Hall effect. By means micromagnetic simulations, used...
Skyrmions are topologically nontrivial, magnetic quasi-particles, that characterized by a topological charge. A regular array of skyrmions - skyrmion crystal (SkX) features the Hall effect (THE) electrons, that, in turn, gives rise to themselves. It is commonly believed antiferromagnetic crystals (AFM-SkXs) lack both effects. In this Rapid Communication, we present generally applicable method create stable AFM-SkXs growing two sublattice SkX onto collinear antiferromagnet. As an example show...
The dispersion relations of magnons in ferromagnetic pyrochlores with Dzyaloshinskii-Moriya interaction are shown to possess Weyl points, i. e., pairs topologically nontrivial crossings two magnon branches opposite topological charge. As a consequence their nature, projections onto surface connected by arcs, thereby resembling closely Fermi arcs electronic semimetals. On top this, the positions points reciprocal space can be tuned widely an external magnetic field: rotated within plane, and...
The Edelstein effect provides the purely electrical generation and control of a homogeneous magnetization in primarily nonmagnetic materials with broken inversion symmetry. Usually, only spin density response to an external electric field is discussed. Here, we report on electrically induced containing as well orbital contributions topological oxide two-dimensional electron gas at interface between SrTiO$_3$ AlO. We find that this particular system exceeds by more than one order magnitude....
We demonstrate theoretically that the thermal Hall effect of magnons in collinear antiferromagnetic insulators is an indicator magnetic and topological phase transitions magnon spectrum. The transversal heat current caused by a gradient calculated for antiferromagnet on honeycomb lattice. An applied field drives system from via spin-flop into field-polarized phase. In addition to these transitions, we find within Both types manifest themselves prominent distinguishing features conductivity,...
The thermal Hall effect, where a transverse heat current is generated in response to longitudinal temperature gradient, probes charge-neutral excitations insulating quantum matter. By studying transport the Heisenberg-Kitaev antiferromagnet and spin liquid candidate Na${}_{2}$Co${}_{2}$TeO${}_{6}$, authors find here that magnon polarons, i.e., hybridized phonons magnons produced by spin-lattice coupling, govern sign magnitude of observed signal. This contrast pure theory, which fails capture...
The electron spin polarization (ESP) of the L-gap surface states on Au(111) is investigated theoretically by means first-principles electronic-structure and photoemission calculations. show a large spin-orbit induced in-plane ESP which perpendicular to wave vector, in close analogy two-dimensional gas with Rashba interaction. corrugation, i.e., asymmetry potential $1\ifmmode\times\else\texttimes\fi{}1$ unit cell, leads small component normal surface. surface-state can be probed qualitatively...
We have used s- and p-polarized synchrotron radiation to image the electronic structure of epitaxial graphene near K-point by angular resolved photoemission spectroscopy (ARPES). Part experimental Fermi surface is suppressed due interference photoelectrons emitted from two equivalent carbon atoms per unit cell graphene's honeycomb lattice. Here we show that rotating polarization vector, are able illuminate this 'dark corridor' indicating present theoretical understanding oversimplified. Our...
We demonstrate that it is possible to tune the Rashba energy, introduced by a strong spin-orbit splitting, and Fermi energy in two-dimensional electron gas controlled change of stoichiometry an artificial surface alloy. In ${\mathrm{Bi}}_{x}{\mathrm{Pb}}_{1\ensuremath{-}x}∕\mathrm{Ag}(111)$ alloy, interaction maintains dramatic influence on band dispersion for arbitrary Bi concentration $x$, as shown angle-resolved photoelectron spectroscopy. The ${E}_{R}$ ${E}_{F}$ can be tuned achieve...
By means of a comprehensive theoretical investigation, we show that external pressure can induce topological phase transitions in IV--VI semiconducting chalcogenides with rocksalt structure. These materials satisfy mirror symmetries are needed to sustain topologically protected surface states, at variance time-reversal symmetry is responsible for gapless edge states ${\mathcal{Z}}_{2}$ insulators. The band inversions high-symmetry points the Brillouin zone related by brought about an...
The hallmark of a skyrmion crystal (SkX) is the topological Hall effect (THE). In this Article, we predict and explain an unconventional behavior conductivity in SkXs. simple terms, spin texture skyrmions causes inhomogeneous emergent magnetic field whose associated Lorentz force acts on electrons. By making homogeneous, THE mapped onto quantum (QHE). Consequently, each electronic band SkX assigned to Landau level. This correspondence QHE allows electrons For example, triangular lattice...
We establish theoretically a thermal Hall effect of collective magnetic excitations in noncollinear but coplanar antiferromagnets. In agreement with superordinate symmetry arguments for linear transport tensors, our findings demonstrate that neither ferromagnetic moment, nor field, scalar spin chirality are indispensable magnon effect. Similar to the electronic anomalous effect, two necessary requirements broken effective time-reversal and point group compatible ferromagnetism. As an...
Using a first-principles Green's function approach we study magnetic properties of the binary tetradymite chalcogenides ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$, ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$, and ${\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$. The coupling between transition-metal impurities is long range, extends beyond quintuple layer, decreases with increasing number $d$ electrons per $3d$ atom. We find two main mechanisms for interaction in these materials: indirect exchange mediated by free...
Using semiclassical Boltzmann transport theory, we predict a current-induced spin polarization in Weyl semimetals, similar to the Edelstein effect of surface states Rashba systems or topological insulators. The theory is applied semimetal TaAs, for which estimate magnitude effect. main contribution comes from states, i.e., Fermi arcs, provide an enormous enhanced by at least one order comparison and
Magnetic skyrmions are envisioned as carriers of information in racetrack storage devices. Unfavorably, the skyrmion Hall effect hinders fast propagation along an applied electric current and limits device's maximum operation speed. In this Rapid Communication, we show that velocity increases by a factor 10 when is suppressed, since straight-line motion allows for application larger driving currents. We consider ferromagnet on heavy metal layer, which converts charge into spin effect. The...
The interplay of spin-orbit coupling (SOC) and magnetism gives rise to a plethora charge-to-spin conversion phenomena that harbor great potential for spintronics applications. In addition the spin Hall effect, magnets may exhibit magnetic effect (MSHE), as was recently discovered [Kimata \textit{et al.}, Nature \textbf{565}, 627-630 (2019)]. To date, MSHE is still awaiting its intuitive explanation. Here we relate vorticity currents in Fermi sea, which explains pictorially origin MSHE. For...
The orbital Hall effect can generate currents of angular momentum more efficiently than the spin in most metals. However, so far, it has only been understood as a steady-state phenomenon. In this theoretical study, is extended into time domain. We investigate momenta and their induced by femtosecond laser pulse Cu nanoribbon. Our numerical simulations provide detailed insights laser-driven electron dynamics on ultrashort timescales with atomic resolution. ultrafast described paper consistent...
We present x-ray diffraction experiments and multiple-scattering calculations on the structure transport properties of a Fe/MgO/Fe(001) magnetic tunnel junction (MTJ). Coherent growth top Fe electrode MgO spacer is observed only for deposition in ambient oxygen atmosphere leading to coherent symmetric MTJ characterized by FeO layers at both interfaces. This goes parallel with indicating large positive magnetoresistance (TMR) values such junctions. The results have important implications...
In the conventional Rashba model for an isotropic two-dimensional electron gas (2DEG), electrons are spin-orbit split by a structural inversion asymmetry (SIA) perpendicular to confinement plane. An additional SIA within plane leads another contribution interaction which is investigated means of nearly-free model. The interplay both contributions manifests itself as enhanced splitting in anisotropic 2DEG, compared case. Further, spin polarization electronic states rotated out Both findings...
A topological insulator is realized via band inversions driven by the spin-orbit interaction. In case of ${\mathcal{Z}}_{2}$ phases, number odd and time-reversal invariance a further unalterable ingredient. For crystalline insulators, may be even but mirror symmetry required. Here, we prove that chalcogenide ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ dual insulator: it simultaneously in phase with invariants...
Ab initio electronic structure calculations based on density functional theory and tight-binding methods for the thermoelectric properties of p-type Sb2Te3 films are presented. The thickness-dependent electrical conductivity thermopower computed in diffusive limit transport Boltzmann equation. Contributions bulk surface to coefficients separated, which enables identify a clear impact topological state properties. When charge carrier concentration is tuned, crossover between...