Berlin 2012 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 8: Electron and spin dynamics
O 8.1: Vortrag
Montag, 26. März 2012, 10:30–10:45, A 060
Empty topological surface state on Bi2Se3 — •Daniel Niesner1, Sergey Eremeev2, Evgueni Chulkov3, and Thomas Fauster1 — 1Universität Erlangen, Lehrstuhl für Festkörperphysik, Staudtstr. 7, 91058 Erlangen, Germany — 2Tomsk State University, pr. Lenina 36, 634050 Tomsk, Russia — 3Donostia International Physics Center (DIPC), and CFM, Centro Mixto CSIC-UPV/EHU, Departamento de Física de Materiales, UPV/EHU, 20080 San Sebastián, Spain
Topological insulators are characterized by spin-polarized, linearly dispersing surface states that arise from a symmetry inversion of the bulk bands at band gap edges. In case of Bi2Se3 the Fermi surface is formed by a single Dirac-cone at the Γ-point.
Using laser-based photoemission with 6.2 eV photon energy we find the Dirac-point 0.3 eV below the Fermi energy.
In mono- and bichromatic two-photon photoemission we find a second linearly dispersing band 1.4 eV above the Fermi level with a group velocity of 5·105m/s. Lifetimes amount to ≈74 fs. Circular dichroism indicates a high degree of spin polarization.
These data are in good agreement with DFT calculations showing a topologically protected surface state 1.5 eV above Fermi level. The calculations compare favorably with the other empty electronic states found in the two-photon photoemission experiments.