Search results for "photoemission"

Orbital origin and matrix element effects in the Ag/Si(111)-()R30° Fermi surface

2007

The Fermi surface (FS) of the Ag/Si(1 1 1)-3×3 reconstruction with an excess of Ag has been mapped by angle resolved photoemission spectroscopy with polarized light in a wide region of the reciprocal space and with different detection geometries. In contrast to previous results, a strong polarization dependence is observed. Applying the dipole selection rules, it is found that the surface state at the Fermi level, S1 state, has odd symmetry with respect to the mirror plane of the honeycomb-chained triangle structure, indicating that it is mainly derived from Ag 5px and 5py orbitals. This conclusion is revised in the new frame of a inequivalent-triangle structure for the Ag/Si(1 1 1)-3×3 at …

2013

The spin texture of a Dirac-type surface state in W(110) lends itself to study spin-dependent effects in electron spectroscopies that show up very clearly. Firstly, we report on spin-resolved photoemission calculations and separate the spin polarization that is attributed to the initial state from that induced by the photoemission process itself. This disentanglement allows one to map spin textures of spin-polarized initial states using circular dichroism, for example from Dirac surface states in topological insulators. Secondly, we demonstrate the mapping of spin-polarized states by spin-dependent two-electron emission. Selecting highly polarized initial states, this spectroscopy can furth…

Energy- and time-resolved microscopy using PEEM: recent developments and state-of-the-art

2008

Two novel methods of spectroscopic surface imaging are discussed, both based on photoemission electron microscopy PEEM. They are characterised by a simple electron-optical set up retaining a linear column. An imaging high-pass energy filter has been developed on the basis of lithographically-fabricated microgrids. Owing to a mesh size of only 7μm, no image distortions occur. The present energy resolution is 70 meV. The second approach employs time-of-flight energy dispersion and time-resolved detection using a Delayline Detector. In this case, the drift energy and the time resolution of the detector determine the energy resolution. The present time resolution is 180 ps, giving rise to an en…

Temperature-Dependent Change of the Electronic Structure in the Kondo Lattice System $YbRh_{2}Si_{2}$

2021

Seminar, Deutschland; Journal of physics / Condensed matter 00(00), 1-20 (2021). doi:10.1088/1361-648X/abe479

Magnetization dynamics in microscopic spin-valve elements: Shortcomings of the macrospin picture

2007

We have studied ultrafast magnetodynamics in micropatterned spin-valve structures using time-resolved x-ray photoemission electron microscopy combined with x-ray magnetic circular dichroism. Exciting the system with ultrafast field pulses of $250\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$ width, we find the dynamic response of the free layer to fall into two distinctly different contributions. On the one hand, it exhibits localized spin wave modes that strongly depend on the shape of the micropattern. A field pulse applied perpendicular to the exchange bias field along the diagonal of a square pattern leads to the excitation of a standing spin wave mode with two nodes along the field direction.…

Accessing fast magnetization dynamics by XPEEM: Status and perspectives

2006

Abstract Being already well established as a versatile technique for high-resolution static magnetic domain imaging, X-ray photoemission electron microscopy (XPEEM) is now also capturing the field of time-resolved magnetic investigations. Using appropriate operation modes at synchrotron radiation sources, a time resolution of 10 ps and less can be achieved in recent magnetodynamics studies, giving access even to phenomena involving precessional processes.

Hard X-ray resonant electronic spectroscopy in transition metal oxides

2005

K-edge X-ray absorption and 2p-XPS spectra of 3d-element oxides present spectral features which cannot be explained within a simple one-electron model. These features reveal the fine electronic structure of transition metal (TM) oxides valence states resulting from hybridized TM-3d and O-2p states, and the correlations between these valence electrons. In this paper, we show how resonant electronic spectroscopy (resonant Auger or resonant photoelectron spectroscopy) around the TM K-edge can be used to interpret the structures of the threshold and, with the help of theoretical calculation, to determine the electronic configuration of the excited ion. Quadrupolar transitions towards localized …

A source of polarized electrons based on photoemission of GaAsP.

1990

Abstract The source described is based on photoemission of electrons from 100-GaAs0.62P0.38 activated to negative electron affinity. It is built to inject a beam of polarized electrons into the 350 MeV linear accelerator in Mainz. It is capable of delivering a mean current of 28 μA spin-polarized longitudinally to a degree of 0.44. The lifetime of the cathode under operational conditions is better than 200 h. The source was successfully run in a parity experiment, in which the analysing power of quasielastic scattering from beryllium for longitudinally polarized electrons was measured.

Aluminum cluster anions: Photoelectron spectroscopy andab initiosimulations

2000

Atomic structures and geometries, electronic structure, and temperature-dependent photoelectron spectra of ${\mathrm{Al}}_{N}^{\ensuremath{-}} (N=19\ensuremath{-}102)$ clusters are studied both theoretically via ab initio local-density-functional simulations, and experimentally with high-resolution measurements. The use of a theoretically well-defined energy shift in conjunction with a generalized Koopmans' theorem enables direct comparisons between the calculated density of states and the experimental photoelectron spectrum. Such comparisons, using photoelectron spectra calculated for various relaxed cluster geometries, enables a determination of the optimal structures of the clusters. The…

Magnetization changes visualized using photoemission electron microscopy

2004

Abstract Photoemission electron microscopy was used to visualize the motion of magnetic domains on a sub-nanosecond timescale. The technique exploits the imaging of magnetic domains using soft X-ray circular dichroism, with the special feature that the instrument utilizes a fast image acquisition system with intrinsic 125 ps time resolution. The overall time resolution used is about 500 ps. Different domains and domain movements have been observed in lithographically-produced Permalloy structures on a copper microstrip-line. A current pulse of I=0.5 A with rise times of about 300 ps switched the Permalloy islands from a Landau-Lifshitz type domain configuration into metastable s-state domai…