Generation of Transient Photocurrents in the Topological Surface State of ${\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$ by Direct Optical Excitation with Midinfrared Pulses

Generation of Transient Photocurrents in the Topological Surface State of ${Sb}_{2} {Te}_{3}$ by Direct Optical Excitation with Midinfrared Pulses

K. Kuroda, J. Reimann, J. Güdde, and U. Höfer

Phys. Rev. Lett. 116, 076801 – Published 17 February 2016

Abstract

We combine tunable midinfrared (mid-IR) pump pulses with time- and angle-resolved two-photon photoemission to study ultrafast photoexcitation of the topological surface state (TSS) of ${Sb}_{2} {Te}_{3}$ . It is revealed that mid-IR pulses permit a direct excitation from the occupied to the unoccupied part of the TSS across the Dirac point. The novel optical coupling induces asymmetric transient populations of the TSS at $\pm k_{∥}$ , which reflects a macroscopic photoexcited electric surface current. By observing the decay of the asymmetric population, we directly investigate the dynamics of the long-lived photocurrent in the time domain. Our discovery promises important advantages of photoexcitation by mid-IR pulses for spintronic applications.