Optical characterization of topological insulator surface states: Berry curvature-dependent response

TL;DR

This paper theoretically investigates how the Berry curvature influences the optical response and photocurrent generation on the surface states of topological insulators, revealing new mechanisms and potential measurement techniques.

Contribution

It extends the understanding of Berry curvature effects on photocurrents beyond quasiclassical approximations and provides explicit formulas for Bi2Se3 surface responses under symmetry-breaking conditions.

Findings

Helicity-dependent photocurrents are significant when symmetry is broken.

Photocurrent growth is linear over time until scattering occurs.

Surface spin response is also dominated by Berry curvature effects.

Abstract

We study theoretically the optical response of the surface states of a topological insulator, especially the generation of helicity-dependent direct current by circularly polarized light. Interestingly, the dominant current, due to an interband transition, is controlled by the Berry curvature of the surface bands. This extends the connection between photocurrents and Berry curvature beyond the quasiclassical approximation where it has been shown to hold. Explicit expressions are derived for the (111) surface of the topological insulator Bi_{2}Se_{3} where we find significant helicity dependent photocurrents when the rotational symmetry of the surface is broken by an in-plane magnetic field or a strain. Moreover, the dominant current grows linearly with time until a scattering occurs, which provides a means for determining the scattering time. The dc spin generated on the surface is also dominated by a linear-in-time, Berry curvature dependent contribution.