title: Ultrafast photocurrents at the surface of the three-dimensional topological insulator Bi2Se3.
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 Bi2Se3with 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.
authors: Fritz Haber Institute of the Max Planck Society, 14195 Berlin, Germany.
authors: Lukas
authors: L
authors: Braun
authors: PGI-9 and JARA-FIT, Forschungszentrum Jülich, 52425 Jülich, Germany.
authors: Gregor
authors: G
authors: Mussler
authors: Institute of Electronic Materials Technology, 01-919 Warsaw, Poland.
authors: Andrzej
authors: A
authors: Hruban
authors: Laboratoire des Solides Irradiés, Ecole Polytechnique, CNRS, CEA, Université Paris-Saclay, 91128 Palaiseau cedex, France.
authors: Marcin
authors: M
authors: Konczykowski
authors: Institut für Physik, Ernst-Moritz-Arndt-Universität Greifswald, 17489 Greifswald, Germany.
authors: Thomas
authors: T
authors: Schumann
authors: Fritz Haber Institute of the Max Planck Society, 14195 Berlin, Germany.
authors: Martin
authors: M
authors: Wolf
authors: Institut für Physik, Ernst-Moritz-Arndt-Universität Greifswald, 17489 Greifswald, Germany.
authors: Markus
authors: M
authors: Münzenberg
authors: Laboratoire des Solides Irradiés, Ecole Polytechnique, CNRS, CEA, Université Paris-Saclay, 91128 Palaiseau cedex, France.
authors: Luca
authors: L
authors: Perfetti
authors: Fritz Haber Institute of the Max Planck Society, 14195 Berlin, Germany.
authors: Tobias
authors: T
authors: Kampfrath