# High-frequency nonlinear transport and photogalvanic effects in two-dimensional topological insulators

## TL;DR

This paper reviews how high-frequency laser radiation induces polarization-dependent dc currents in the edges of 2D topological insulators, exploring phenomenological descriptions and microscopic mechanisms of photocurrent generation.

## Contribution

It provides a comprehensive overview of both theoretical and experimental insights into edge photoelectric effects in 2D topological insulators, highlighting new mechanisms and effects.

## Key findings

- Edge photocurrents depend on radiation polarization and edge symmetry.
- Microscopic mechanisms include direct, indirect, and edge-to-bulk optical transitions.
- Photogalvanic and photon drag effects contribute to photocurrent generation.

## Abstract

Excitation of a topological insulator by a high-frequency electric field of a laser radiation leads to a dc electric current in the helical edge channel whose direction and magnitude are sensitive to the radiation polarization and depend on the physical properties of the edge. We present an overview of theoretical and experimental studies of such edge photoelectric effects in two-dimensional topological insulators based on semiconductor quantum wells. First, we give a phenomenological description of edge photocurrents, which may originate from the photogalvanic effects or the photon drag effects, for edges of all possible symmetry. Then, we discuss microscopic mechanisms of photocurrent generation for different types of optical transitions involving helical edge states. They include direct and indirect optical transitions within the edge channel and edge-to-bulk optical transitions.