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

TL;DR

This study demonstrates cyclotron resonance induced photocurrents in the surface states of a 3D topological insulator based on strained HgTe, revealing insights into carrier dynamics and providing a new method to probe surface state properties.

Contribution

It is the first to observe and analyze cyclotron resonance induced photocurrents in topological insulator surface states using terahertz radiation and gated measurements.

Findings

Photocurrents are generated in topologically protected surface states.

Cyclotron resonance of bulk carriers detected at high gate voltages.

Photocurrent response enables probing of surface state effective masses and mobility.

Abstract

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 photocurrent formation is supported by complimentary measurements of magneto-transport and radiation transmission. We demonstrate that the photocurrent is generated in the topologically protected surface states. Studying the resonance response in a gated sample we examined the behavior of the photocurrent, which enables us to extract the mobility and the cyclotron mass as a function of the Fermi energy. For high gate voltages we also detected cyclotron resonance (CR) of bulk carriers, with a mass about two times larger than that obtained for the surface states. The origin of the CR assisted photocurrent is discussed in terms of asymmetric scattering of TI surface carriers in the momentum space. Furthermore, we show that studying the photocurrent in gated samples provides a sensitive method to probe the effective masses and the mobility of 2D Dirac surface states, when the Fermi level lies in the bulk energy gap or even in the conduction band.