Regensburg 2022 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 9: Ultrafast Electron Dynamics at Surfaces and Interfaces 2
O 9.9: Vortrag
Montag, 5. September 2022, 17:00–17:15, H3
Pump helicity-dependent anisotropic population dynamics in the topological insulator Sb2Te3 — •Jan Böhnke1, Haydar Altug Yildirim1,3, Stephan Schmutzler1, Jaime Sánchez-Barriga2, Oliver Rader2, Cornelius Gahl1, and Martin Weinelt1 — 1Fachbereich Physik, Freie Universität Berlin, Berlin, Germany — 2Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Berlin, Germany — 3Leibniz-Institut für Astrophysik, Potsdam, Germany
The specific spin texture of Dirac cone like topologically protected surface states (TSS) and the long electron mean free path allow for spin-polarized currents at the surface of topological insulators. Optical control of such currents has been discussed controversially.
We investigated the role of direct and indirect population channels for the unoccupied TSS on Sb2Te3 in 2D momentum space by time and angle-resolved two-photon photoemission spectroscopy. Excitation with 1.55 eV photons leads to an initially anisotropic population of the Dirac cone, dependent on the helicity of the excitation pulse and the azimuthal orientation of the sample. The strongest anisotropy is found in the energy range of the warped Dirac cone. It exhibits predominantly a 3-fold symmetry originating from the symmetry group of the bulk material. This contribution accordingly does not correspond to a macroscopic current in the TSS. On a time scale of 100 fs the population anisotropy is masked by electrons scattering from the bulk conduction band into the TSS.