Symmetry regimes for circular photocurrents in monolayer MoSe2

TL;DR

This paper investigates the symmetry, spectral, and electrical properties of circular photocurrents in monolayer MoSe2, revealing two distinct contributions influenced by device symmetry and ruling out Berry curvature effects.

Contribution

It provides a detailed analysis of the symmetry requirements and physical origins of circular photocurrents in monolayer MoSe2, distinguishing between different voltage-dependent contributions.

Findings

Two different CPC contributions dominate at different voltages.

Device symmetry reduction is necessary for observed CPC effects.

Berry curvature does not significantly contribute to CPC in this system.

Abstract

In monolayer transition metal dichalcogenides helicity-dependent charge and spin photocurrents can emerge, even without applying any electrical bias, due to circular photogalvanic and photon drag effects. Exploiting such circular photocurrents (CPC) in devices, however, requires better understanding of their behavior and physical origin. Here, we present symmetry, spectral, and electrical characteristics of CPC from excitonic interband transitions in a MoSe2 monolayer. The dependence on bias and gate voltages reveals two different CPC contributions, dominant at different voltages and with different dependence on illumination wavelength and incidence angles. We theoretically analyze symmetry requirements for effects that can yield CPC and compare these with the observed angular dependence and symmetries that occur for our device geometry. This reveals that the observed CPC effects require a reduced device symmetry, and that effects due to Berry curvature of the electronic states do not give a significant contribution.