A5088356388- Magnetic properties of thin films
- Quantum and electron transport phenomena
- Surface and Thin Film Phenomena
- Topological Materials and Phenomena
- Advanced Chemical Physics Studies
- Electron and X-Ray Spectroscopy Techniques
- Graphene research and applications
- Physics of Superconductivity and Magnetism
- Rare-earth and actinide compounds
- X-ray Spectroscopy and Fluorescence Analysis
- Semiconductor materials and devices
- Nuclear Physics and Applications
- Advanced Electron Microscopy Techniques and Applications
- Advanced Condensed Matter Physics
- Particle Accelerators and Free-Electron Lasers
- Advanced X-ray Imaging Techniques
- Radiation Detection and Scintillator Technologies
- Electronic and Structural Properties of Oxides
- Nuclear physics research studies
- Spectroscopy and Laser Applications
- Electromagnetic Scattering and Analysis
- Copper Interconnects and Reliability
- Graph theory and applications
- Magneto-Optical Properties and Applications
- Graph Labeling and Dimension Problems
TRIUMF
2019-2023
University of Münster
2011-2021
Max-Born-Institute for Nonlinear Optics and Short Pulse Spectroscopy
2005-2012
Freie Universität Berlin
2006-2010
Friedrich-Alexander-Universität Erlangen-Nürnberg
2006
Lawrence Berkeley National Laboratory
2004
University of Cologne
2001
We report on a combined experimental and theoretical study of the spin-dependent relaxation processes in electron system an iron film Cu(100). Spin-, time-, energy- angle-resolved two-photon photoemission shows strong characteristic dependence lifetime photoexcited electrons their spin energy. Ab initio calculations as well many-body treatment corroborate that observed properties are determined by involving magnon emission. Thereby we demonstrate emission hot occurs femtosecond time scale...
We present a combined experimental and theoretical study on the unoccupied surface electronic structure of $\mathrm{Tl}/\mathrm{Si}(111)$ surface. Spin- angle-resolved inverse-photoemission measurements with sensitivity to both in-plane out-of-plane polarization direction detect spin-orbit-split state, which is well described by calculations. demonstrate that spin vector rotates from classical Rashba around $\overline{\ensuremath{\Gamma}}$ perpendicular at...
We present a combined experimental and theoretical study of spin–orbit-induced spin splittings in the unoccupied surface electronic structure prototypical Rashba system Au(111). Spin- angle-resolved inverse-photoemission measurements reveal Rashba-type splitting part L-gap state. With increasing momentum parallel to surface, spectral intensity is lowered vanishes as state approaches band-gap boundary. Furthermore, we observe significantly spin-dependent peak positions intensities for...
Exchange splitting and dynamics of image-potential states in front a 3 monolayer iron film on Cu(100) have been studied with time-, energy-, spin-resolved bichromatic two-photon photoemission. For the first state n=1 we observe an exchange 56 +/- 10 meV spin-dependent lifetimes 16 2 fs for majority-spin 11 minority-spin electrons, respectively. The time-resolved studies both population linewidth manifest that at magnetic surface not only inelastic but also quasielastic scattering processes...
Linear magnetic dichroism is observed in spin-, time-, and energy-resolved two-photon photoemission from valence bands of epitaxial fcc cobalt on Cu(001). With image-potential states as spectator we identify initial bulk surface with minority spin character the source for dichroic intensities apparent lifetimes. Excellent agreement ab initio fully relativistic calculations band structure allows us to precisely determine spin-orbit hybridization points close Fermi level. These hot spots...
The spin texture of the unoccupied bands surface alloy Bi/Ag(111) is investigated with spin- and angle-resolved inverse photoemission first-principles calculations. Surprisingly, measured character does not always reflect calculated bands. With help calculations within one-step model, however, discrepancy traced back to influence orbital symmetry respective states in combination experimental geometry. In particular, show that a band mixed symmetries may neither be recovered s- nor p-...
The spin-dependent lifetimes of hot electrons in fcc Co films were studied by spin- and time-resolved two-photon photoemission. Even for excitation energies close to the Fermi level, we find almost identical majority minority electrons. This result contradicts ab initio theories predicting 5 10 times longer $3d$ ferromagnets. We provide direct experimental evidence that this discrepancy is caused dominance exchange scattering inelastic electron decay, combination with secondary latter are...
The magnetic exchange splitting of electronic states in a 7 monolayer Fe film on Cu(001) was investigated below and above the Curie temperature T(C), using image-potential surface as sensor. At long-range order breaks down reflected by vanishing spin polarization. splitting, contrast, does not change abruptly at T(C) but persists up to T=1.2T(C). Equally, spin-integrated linewidth shows no signature phase transition smoothly decreases with increasing temperature. Our experimental results...
We present a ROtatable Spin-polarized Electron source (ROSE) for the use in spin- and angle-resolved inverse-photoemission (SR-IPE) experiments. A key feature of ROSE is variable direction transversal electron beam polarization. As result, experiment becomes sensitive to two orthogonal in-plane polarization directions, and, nonnormal incidence, out-of-plane component. characterize test its performance on basis SR-IPE Measurements magnetized Ni films W(110) serve as reference demonstrate spin...
The Tl/Si(111)-$(1\ifmmode\times\else\texttimes\fi{}1)$ surface features outstanding properties with a unique spin pattern in momentum space. Along $\overline{\ensuremath{\Gamma}}\overline{K}$ $(\overline{\ensuremath{\Gamma}}{\overline{K}}^{\ensuremath{'}})$, states rotating had been observed. Here, the focus is put on unoccupied electronic structure along $\overline{\ensuremath{\Gamma}}\overline{M}$ high-symmetry direction. Spin- and angle-resolved inverse-photoemission experiments...
A remarkably large spin signal is observed on nonmagnetic W(110) for a highly symmetric unoccupied state with no intrinsic polarization. The magnitude and, more importantly, the sign of this signal, measured by spin- and angle-resolved inverse photoemission normal electron incidence, can be tuned in user-defined manner variation photon-detection angle and/or rotating spin-polarization direction incident electrons. Using calculations orbitally decomposed spectral densities, effect traced back...
In a joint theoretical and experimental investigation we show that series of transition metals with strained body-centered cubic lattice ---W, Ta, Nb, Mo--- host surface states are topologically protected by mirror symmetry. Our finding extends the class nontrivial systems topological crystalline metals. The is based on independent calculations electronic structures invariants, results which agree established properties Dirac-type state in W(110). To further support our prediction,...
The electronic structure and spin texture around the $\overline{\mathrm{M}}$ point of $\mathrm{Tl}/\mathrm{Si}(111)\text{\ensuremath{-}}(1\ifmmode\times\else\texttimes\fi{}1)$ is investigated with spin- angle-resolved inverse photoemission density-functional theory. surface exhibits a surface-derived unoccupied state, which extends over complete Brillouin zone. It known for its giant spin-orbit-induced splitting unique symmetry- landscape: rotating pattern in momentum space along...
We present a method to determine the electron beam divergence, and thus momentum resolution, of an inverse-photoemission setup directly from series spectra measured on Cu(111). Simulating these with different divergences shows distinct influence divergence appearance Shockley surface state. Upon crossing Fermi level, its rise in intensity can be linked divergence. A comparison measurement simulation enables us quantify resolution independent quality, energy experimental geometry. With spin...
In topological insulators (TIs), spin-orbit coupling leads to the emergence of metallic surface states crossing fundamental band gap. They exhibit a Dirac-cone-like dispersion with helical spin structure. Bi${}_{2}$Se${}_{3}$(111) is most prominent prototypical TI featuring simple structure single Dirac cone close Fermi level around center Brillouin zone. Due interesting structure, TIs have emerged as promising materials in field spintronics and optospintronics. Ultrafast light pulses might...
Inverse photoemission is the most versatile experimental tool to study unoccupied electronic structure at surfaces of solids. Typically, experiments are performed in isochromat mode with bandpass photon detectors. For gas-filled counters, behavior realized by combination photoionization threshold counting gas as high-pass filter and ultraviolet transmission cutoff an alkaline earth fluoride entrance window low-pass filter. The characteristics determine optical bandpass. performance counter...
Modern angle-resolved photoemission spectroscopy (ARPES) measures the electronic structure of a sample with parallel detection energy and momentum. Spin resolution, increasingly important for study nonmagnetic samples such as topological insulators, is, however, still restricted to single-channel mode. The authors show feasibility oxygen-passivated iron polarizing electron mirror in future spin-resolving display-type analyzers.
The surface electronic structure of face-centred-cubic cobalt films on Cu(0 0 1) was studied by spin-resolved one- and two-photon photoemission. A minority state in a Δ1-symmetry gap the band-structure identified at about 0.45 eV below Fermi energy. This causes resonance-like enhancement population image-potential two-photon-photoemission experiment excited p-polarized light. Additionally, it appears as surface-sensitive spectral feature normal photoemission (PE) its existence is confirmed...
Tantalum and tungsten, direct neighbors in the periodic table, exhibit a very similar electronic structure. Compared with however, bands of tantalum are less occupied due to lack one electron. As consequence, an exceptional Dirac-cone-like surface state, observed below Fermi level for W(110), may appear above Ta(110). To prove this conjecture, we investigate unoccupied structure Ta(110) by spin- angle-resolved inverse photoemission electronic-structure calculations. Surprisingly, our results...
The spin texture of the unoccupied surface electronic structure metal-semiconductor hybrid system $\mathrm{Tl}/\mathrm{Ge}(111)\ensuremath{-}(1\ifmmode\times\else\texttimes\fi{}1)$ is investigated by spin- and angle-resolved inverse photoemission as well quasiparticle band-structure calculations. Spin-polarized bands with rotating giant energy splitting are found along $\overline{\mathrm{\ensuremath{\Gamma}}}\overline{K}({\overline{K}}^{\ensuremath{'}})$, forming valleys alternating...
A surface state of ${d}_{{z}^{2}}$ symmetry is identified on Y(0001) at about 0.1 eV above the Fermi level by a combined direct and inverse photoemission experiment. The spectral signatures this appear both sides are equally quenched upon formation monoxide. Concurrently, new interface appears $\ensuremath{-}0.7\text{ }\text{eV}$ intensity remains 0.6 eV, which attributed to transitions into bulk bands gap edge. This detailed analysis electronic structure gains in importance when applied...