Regensburg 2016 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 74: Ultrafast Electron and Spin Dynamics at Interfaces

O 74.4: Poster

Mittwoch, 9. März 2016, 18:15–20:30, Poster A

Resonant excitation and circular dichroism of the second Dirac cone of the topological insulator Bi₂Se₃ — •Sophia Ketterl¹, Sebastian Otto², Martin Bastian¹, Cornelius Gahl¹, Thomas Fauster², and Martin Weinelt¹ — ¹Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany — ²Universität Erlangen-Nürnberg, Staudtstr. 7, 91058 Erlangen, Germany

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 dispersion is occupied. Two-photon photoemission (2PPE) experiments have shown that Bi₂Se₃ exhibits a second Dirac cone in the band gap between the second and third conduction band [1].

We studied the properties of the second Dirac cone of Bi₂Se₃ by 2PPE with both linearly and circularly polarized light. We show that the second Dirac cone can be populated directly from the first Dirac cone by photoexcitation with 1.7 eV photon energy. We observe dichroic photoemission for both circularly polarized probe and pump pulses. This hints at a helical spin structure of the second Dirac cone [1] and its asymmetric population, respectively. Both are necessary to create photocurrents with a definite spin polarization.
We studied the temporal evolution of the transient population of the second Dirac cone in order to understand how inter- and intraband scattering influences photocurrents within the TSS.

[1] D. Niesner et. al., Phys. Rev. B 86, 205403 (2012).