Optical valleytronics of impurity states in two-dimensional Dirac materials

TL;DR

This paper investigates how impurity states in two-dimensional Dirac materials like MoS2 influence valley-specific optical transitions, revealing valley-dependent selection rules and their effects on optical absorption and photocurrent.

Contribution

It provides an analytical model for impurity-induced optical transitions in 2D Dirac materials, elucidating valley selection rules and their impact on optical and electronic responses.

Findings

Valley-dependent optical selection rules are established.

Impurity states significantly affect optical absorption spectra.

Photon-drag current is influenced by impurity-band transitions.

Abstract

We analyze the valley selection rules for optical transitions from impurity states to the conduction band in two-dimensional Dirac materials, taking a monolayer of MoS2 as an example. We employ the analytical model of a shallow impurity potential which localizes electrons described by a spinor wave function, and, first, find the system eigenstates taking into account the presence of two valleys in the Brillouin zone. Then, we find the spectrum of the absorbance and calculate the photon-drag electric current due to the impurity-band transitions, drawing the general conclusions regarding the valley optical selection rules for the impurity-band optical transitions in gapped Dirac materials.