Linear photogalvanic effect in surface states of topological insulators

TL;DR

This paper develops a theoretical model for the linear photogalvanic effect in topological insulator surface states, highlighting the roles of shift and ballistic contributions and their dependence on light polarization and intensity.

Contribution

The study introduces a comprehensive theory distinguishing shift and ballistic contributions to the photogalvanic effect in topological insulators, including their frequency and intensity dependencies.

Findings

Ballistic and shift contributions are of the same order of magnitude.

Ballistic contribution dominates in the nonlinear regime due to saturation.

Photocurrent dependence on polarization is primarily due to ballistic effects in nonlinear conditions.

Abstract

Theory of the Linear photogalvanic effect is developed for direct optical transitions between surface states of three-dimensional topological insulators. The photocurrent governed by the orientation of the polarization plane of light and caused by the warping of the energy dispersion of two-dimensional carriers is calculated. It is shown that both the shift contribution caused by coordinate shifts of the particle wavepackets during the optical transitions and the ballistic contribution caused by interference of the optical absorption and scattering by disorder have generally the same order of magnitude. The ballistic contribution is present owing to electron-hole asymmetry of topological surface states and has a frequency dependence in contrast to the shift photocurrent. In the nonlinear in the light intensity regime appearing due to saturation of the direct optical transitions the ballistic contribution dominates. The nontrivial dependence of the photocurrent on the polarization plane orientation in the nonlinear regime appears solely due to the ballistic contribution. Our findings allow separating the ballistic and shift contributions to the Linear photogalvanic current in experiments.