Control over topological insulator photocurrents with light polarization

TL;DR

This study demonstrates that circularly and linearly polarized light can generate and control photocurrents in topological insulators, revealing new opto-electronic responses of topological surface states and enabling potential spintronic applications.

Contribution

First experimental observation of photocurrents driven by polarized light in a topological insulator, linking light polarization to topological surface state responses.

Findings

Circularly polarized light reverses photocurrent direction.

Linear polarization controls the magnitude and direction of photocurrents.

Photocurrents originate from topological helical Dirac fermions.

Abstract

Three-dimensional topological insulators represent a new quantum phase of matter with spin-polarized surface states that are protected from backscattering. The static electronic properties of these surface states have been comprehensively imaged by both photoemission and tunneling spectroscopies. Theorists have proposed that topological surface states can also exhibit novel electronic responses to light, such as topological quantum phase transitions and spin-polarized electrical currents. However, the effects of optically driving a topological insulator out of equilibrium have remained largely unexplored experimentally, and no photocurrents have been measured. Here we show that illuminating the topological insulator Bi2Se3 with circularly polarized light generates a photocurrent that originates from topological helical Dirac fermions, and that reversing the helicity of the light reverses the direction of the photocurrent. We also observe a photocurrent that is controlled by the linear polarization of light, and argue that it may also have a topological surface state origin. This approach may allow the probing of dynamic properties of topological insulators and lead to novel opto-spintronic devices.