Ultrafast photocurrents at the surface of the three-dimensional topological insulator Bi 2 Se 3

Lukas Braun (1) , Gregor Mussler (2) , Andrzej Hruban (3) , Marcin Konczykowski (4) , Thomas Schumann (5) , Martin Wolf (1) , Markus Münzenberg (5) , Luca Perfetti (4) , Tobias Kampfrath (1)

1 FHI - Fritz-Haber-Institut der Max-Planck-Gesellschaft
2 PGI-9 and JARA-FIT, Forschungszentrum Ju¨lich, 52425 Ju¨lich, Germany
3 Institute of Electronic Materials Technology, 01-919 Warsaw, Poland
4 LSI - Laboratoire des Solides Irradiés - Irradiated Solids Laboratory
5 Institut für Physik [Greifswald]

Three-dimensional topological insulators are fascinating materials with insulating bulk yet metallic surfaces that host highly mobile charge carriers with locked spin and momentum. Remarkably, surface currents with tunable direction and magnitude can be launched with tailored light beams. To better understand the underlying mechanisms, the current dynamics need to be resolved on the timescale of elementary scattering events (B10 fs). Here, we excite and measure photocurrents in the model topological insulator Bi 2 Se 3 with a time resolution of 20 fs by sampling the concomitantly emitted broadband terahertz (THz) electromagnetic field from 0.3 to 40 THz. Strikingly, the surface current response is dominated by an ultrafast charge transfer along the Se–Bi bonds. In contrast, photon-helicity-dependent photocurrents are found to be orders of magnitude smaller than expected from generation scenarios based on asymmetric depopulation of the Dirac cone. Our findings are of direct relevance for broadband optoelectronic devices based on topological-insulator surface currents.

Mots clés: topological insulators; terahertz spectroscopy

Domaines: Matière Condensée [cond-mat]

Lukas Braun, Gregor Mussler, Andrzej Hruban, Marcin Konczykowski, Thomas Schumann, et al.. Ultrafast photocurrents at the surface of the three-dimensional topological insulator Bi 2 Se 3. Nature Communications, 2016, 7, pp.13259. ⟨10.1038/ncomms13259⟩. ⟨hal-01445495⟩