Kristian Döbrich
Free University of Berlin
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Publication
Featured researches published by Kristian Döbrich.
New Journal of Physics | 2008
Annette Pietzsch; A. Föhlisch; M. Beye; M Deppe; Franz Hennies; Mitsuru Nagasono; Edlira Suljoti; W. Wurth; Cornelius Gahl; Kristian Döbrich; Alexey Melnikov
We have performed core level photoelectron spectroscopy on a W(110) single crystal with femtosecond XUV pulses from the free-electron laser at Hamburg (FLASH). We demonstrate experimentally and through theoretical modelling that for a suitable range of photon fluences per pulse, time-resolved photoemission experiments on solid surfaces are possible. Using FLASH pulses in combination with a synchronized optical laser, we have performed femtosecond time-resolved core-level photoelectron spectroscopy and observed sideband formation on the W 4f lines indicating a cross correlation between femtosecond optical and XUV pulses.
Physical Review B | 2005
O. Krupin; Gustav Bihlmayer; K. Starke; Serguei Gorovikov; J. E. Prieto; Kristian Döbrich; Stefan Blügel; G. Kaindl
Exchange-split two-dimensional electronic states at the magnetic Gd(0001) surface change their energy dispersion upon magnetization reversal owing to the Rashba effect. The Rashba parameter is found to be substantially enhanced and to change sign when an epitaxial metal-oxide surface layer is formed. The experimental observations are quantitatively described by ab initio calculations giving a detailed account of the near-surface charge-density gradients that are responsible for the Rashba effect.
Review of Scientific Instruments | 2013
Björn Frietsch; Robert Carley; Kristian Döbrich; Cornelius Gahl; Martin Teichmann; Olaf Schwarzkopf; Ph. Wernet; Martin Weinelt
We present a table top setup for time- and angle-resolved photoelectron spectroscopy to investigate band structure dynamics of correlated materials driven far from equilibrium by femtosecond laser pulse excitation. With the electron-phonon equilibration time being in the order of 1-2 ps it is necessary to achieve sub-picosecond time resolution. Few techniques provide both the necessary time and energy resolution to map non-equilibrium states of the band structure. Laser-driven high-order harmonic generation is such a technique. In our experiment, a grating monochromator delivers tunable photon energies up to 40 eV. A photon energy bandwidth of 150 meV and a pulse duration of 100 fs FWHM allow us to cover the k-space necessary to map valence bands at different kz and detect outer core states.
New Journal of Physics | 2009
Oleg Krupin; Gustav Bihlmayer; Kristian Döbrich; J. E. Prieto; K. Starke; Serguei Gorovikov; Stefan Blügel; Steve Kevan; G. Kaindl
We present a systematic study of the Rashba-type spin–orbit interaction at the (0001) surfaces of rare-earth metals and their surface monoxides, specifically of Tb metal and the O/Tb, O/Lu and O/Y surfaces. By means of photoemission experiments and ab initio band-structure calculations, we uncover the influence of this interaction on the surface electronic structure. In turn, the dramatic impact of the charge-density distribution of the surface/interface states on the strength of the Rashba-type spin splitting is demonstrated. We discuss the Rashba effect at magnetic and non-magnetic rare-earth surfaces, and compare with cases where it is negligible. The difference between the Rashba effect and magnetic linear dichroism in photoemission is pointed out to help avoid possible confusion in connection with the simultaneous appearance of these two effects at a magnetic surface.
Physical Review Letters | 2008
Kristian Döbrich; Marko Wietstruk; J. E. Prieto; F. Heigl; O. Krupin; K. Starke; G. Kaindl
For epitaxial trilayers of the magnetic rare-earth metals Gd and Tb, exchange coupled through a nonmagnetic Y spacer layer, element-specific hysteresis loops were recorded by the x-ray magneto-optical Kerr effect at the rare-earth M5 thresholds. This allowed us to quantitatively determine the strength of interlayer exchange coupling (IEC). In addition to the expected oscillatory behavior as a function of spacer-layer thickness dY, a temperature-induced sign reversal of IEC was observed for constant dY, arising from magnetization-dependent electron reflectivities at the magnetic interfaces.
european quantum electronics conference | 2011
Robert Carley; Björn Frietsch; Kristian Döbrich; Martin Teichmann; Cornelius Gahl; Olaf Schwarzkopf; Philippe Wernet; Frank Noack; Martin Weinelt
The Lanthanide metals gadolium (Gd) and terbium (Tb) are prototypical local-moment ferromagnets. In these systems the magnetic moment derives predominantly from the partial occupancy of the localized 4f core electronic levels. Alignment of the magnetic moments between adjacent atoms in the lattice occurs by spin polarization of the itinerant 5d and 6s valence electrons in an indirect exchange (Ruderman-Kittel-Kasuya-Yosida) interaction.
Archive | 2009
Cornelius Gahl; A. Azima; M. Beye; M Deppe; Kristian Döbrich; U. Hasslinger; Franz Hennies; Alexey Melnikov; Mitsuru Nagasono; Annette Pietzsch; Martin Wolf; W. Wurth; A. Föhlisch
Using the high peak brilliance of the X-ray Free-Electron Laser at Hamburg, we have studied the X-ray pulse induced transient optical reflectivity on GaAs and establish a novel tool for fs X-ray/optical cross-correlation
Physical Review B | 2005
J. E. Prieto; O. Krupin; Serguei Gorovikov; Kristian Döbrich; G. Kaindl; K. Starke
The epitaxial system Sm/Co(0001) was studied for Sm coverages up to 1 monolayer (ML) on top of ultrathin Co/W(110) epitaxial films. Two ordered phases were found for 1/3 and 1 ML Sm, respectively. The valence state of Sm was determined by means of photoemission and magnetic properties were measured by magneto-optical Kerr effect. We find that 1 ML Sm causes a strong increase of the coercivity with respect to that of the underlying Co film. Element-specific hysteresis loops, measured by using resonant soft x-ray reflectivity, show the same magnetic behavior for the two elements.
Nature Photonics | 2008
Cornelius Gahl; Armin Azima; M. Beye; Martin Deppe; Kristian Döbrich; Urs Hasslinger; Franz Hennies; Alexej Melnikov; Mitsuru Nagasono; Annette Pietzsch; Martin Wolf; W. Wurth; A. Föhlisch
Physical Review Letters | 2012
Robert Carley; Kristian Döbrich; Björn Frietsch; Cornelius Gahl; Martin Teichmann; Olaf Schwarzkopf; Philippe Wernet; Martin Weinelt