Ultrafast photocurrents at the surface of the three-dimensional topological insulator Bi2Se3

Lukas Braun (), Gregor Mussler, Andrzej Hruban, Marcin Konczykowski, Thomas Schumann, Martin Wolf, Markus Münzenberg, Luca Perfetti and Tobias Kampfrath ()
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Lukas Braun: Fritz Haber Institute of the Max Planck Society
Gregor Mussler: PGI-9 and JARA-FIT, Forschungszentrum Jülich
Andrzej Hruban: Institute of Electronic Materials Technology
Marcin Konczykowski: Laboratoire des Solides Irradiés, Ecole Polytechnique, CNRS, CEA, Université Paris-Saclay
Thomas Schumann: Institut für Physik, Ernst-Moritz-Arndt-Universität Greifswald
Martin Wolf: Fritz Haber Institute of the Max Planck Society
Markus Münzenberg: Institut für Physik, Ernst-Moritz-Arndt-Universität Greifswald
Luca Perfetti: Laboratoire des Solides Irradiés, Ecole Polytechnique, CNRS, CEA, Université Paris-Saclay
Tobias Kampfrath: Fritz Haber Institute of the Max Planck Society

Nature Communications, 2016, vol. 7, issue 1, 1-9

Abstract: Abstract 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 (∼10 fs). Here, we excite and measure photocurrents in the model topological insulator Bi2Se3 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.

Date: 2016
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DOI: 10.1038/ncomms13259

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