SurfaceScience21 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 92: Poster Session VII: Ultrafast electron dynamics at surface and interfaces III

O 92.6: Poster

Donnerstag, 4. März 2021, 10:30–12:30, P

Ultrafast dynamics of direct and indirect excitation pathways of the topologically protected surface state on Sb2Te3 — •Jan Böhnke¹, Haydar Altug Yildirim¹, Cornelius Gahl¹, Jaime Sánchez-Barriga², Oliver Rader², and Martin Weinelt¹ — ¹Fachbereich Physik, Freie Universität Berlin, Germany — ²Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Germany

Dirac cone like topologically protected surface states (TSS) have attracted high interest for spintronic applications due to their specific spin texture in momentum space and the long electron mean free path because of reduced scattering phase space. Optical control of electric currents at the surface of topological insulators has been discussed controversially. We investigated the role of direct and indirect population channels for the 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 depending on the helicity of the excitation pulse. This circular dichroism however predominantly exhibits a 3-fold symmetry, which reflects the symmetry group of the bulk material but does not correspond to a macroscopic current in the TSS. Since the photon energy exceeds the bulk band gap, the optical excitation creates also a significant electron population in the conduction band, which relaxes towards the band minimum on the timescale of few 100 fs. On the same timescale electrons scattered from the conduction band dominate the population in the TSS so that the anisotropy decays rapidly.