Cyclotron Resonance Assisted Photocurrents in Surface States of a 3D Topological Insulator Based on a Strained High Mobility HgTe Film

摘要

We report on the observation of cyclotron resonance induced photocurrents,excited by continuous wave terahertz radiation, in a 3D topological insulator(TI) based on an 80 nm strained HgTe film. The analysis of the photocurrentformation is supported by complimentary measurements of magneto-transport andradiation transmission. We demonstrate that the photocurrent is generated inthe topologically protected surface states. Studying the resonance response ina gated sample we examined the behavior of the photocurrent, which enables usto extract the mobility and the cyclotron mass as a function of the Fermienergy. For high gate voltages we also detected cyclotron resonance (CR) ofbulk carriers, with a mass about two times larger than that obtained for thesurface states. The origin of the CR assisted photocurrent is discussed interms of asymmetric scattering of TI surface carriers in the momentum space.Furthermore, we show that studying the photocurrent in gated samples provides asensitive method to probe the effective masses and the mobility of 2D Diracsurface states, when the Fermi level lies in the bulk energy gap or even in theconduction band.