# Cyclotron resonance induced photogalvanic effect in surface states of 200 nm thick strained HgTe films

## TL;DR

This study demonstrates a giant resonant photocurrent induced by cyclotron resonance in surface states of strained HgTe films, revealing topologically protected surface states in thick HgTe films through magneto-photogalvanic and magnetotransport measurements.

## Contribution

It provides evidence of topologically protected surface states in 200 nm thick HgTe films via cyclotron resonance-induced photocurrent and magnetotransport analysis, extending understanding of topological insulators.

## Key findings

- Resonant photocurrent caused by cyclotron resonance in HgTe surface states.
- Resonance positions nearly coincide in strained and fully gapped HgTe films.
- Magnetotransport experiments support the existence of topologically protected surface states.

## Abstract

We report on the study of magneto-photogalvanic and magnetotransport phenomena in 200 nm partially strained HgTe films. This thickness is slightly larger than the estimated critical thickness of lattice relaxation leaving the film partially relaxed with the value of the energy gap close to zero. We show that illumination of HgTe films with monochromatic terahertz laser radiation results in a giant resonant photocurrent caused by the cyclotron resonance in the surface states. The resonant photocurrent is also detected in the reference fully strained 80 nm HgTe films previously shown to be fully gapped 3D topological insulators. We show that the resonance positions in both types of films almost coincide demonstrating the existence of topologically protected surface states in thick HgTe films. The conclusion is supported by magnetotransport experiments.