Dresden 2017 – scientific programme
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O: Fachverband Oberflächenphysik
O 75: Ultrafast Electron and Spin Dynamics
O 75.5: Talk
Wednesday, March 22, 2017, 16:00–16:15, TRE Phy
On the origin of photocurrents in the topological insulator Bi2Se3 — •Sophia Ketterl1, Sebastian Otto2, Martin Bastian1, Cornelius Gahl1, Beatrice Andres1, Jan Minar3, Hubert Ebert3, Thomas Fauster2, Jürgen Braun3, and Martin Weinelt1 — 1Freie Universität Berlin, Arnimallee 14, 14195 Berlin — 2Friedrich-Alexander-Universität Erlangen-Nürnberg, Staudtstr. 7, 91058 Erlangen — 3Ludwig-Maximilians-Universität München, Butenandtstr. 5-13, 81377 München
Topological insulators (TIs) host metallic topological surface states (TSS) with helical spin structure. This makes them promising materials for the generation of spin-polarized currents. The TI Bi2Se3 is intrinsically n-doped and thus the TSS at the Γ point with a Dirac cone (DC) dispersion is occupied. Two-photon photoemission (2PPE) experiments have shown that Bi2Se3 exhibits a second, unoccupied DC in the band gap between the second and third conduction band [1].
We studied the excitation of photocurrents with circularly polarized light in the second DC with 2PPE and one-step photoemission calculations. The second DC can be populated from the first DC. We find dichroic photoemission for circularly polarized pump pulses, both at resonant and off-resonant excitation. Only for excitation out of the occupied conduction band, we observe an asymmetric electron population indicating a photocurrent. Thus our results question the topological origin of photocurrents in Bi2Se3 for near-IR excitation [2].
[1] D. Niesner et. al., Phys. Rev. B 86, 205403 (2012).
[2] C. Kastl et. al., Nat. Commun. 6, 6617 (2015).