Edge states and spin-valley edge photocurrent in transition metal dichalcogenide monolayers

TL;DR

This paper presents an analytical theory of edge states in transition metal dichalcogenide monolayers, revealing how edge spin-orbit interaction influences their dispersion and how circularly polarized light can generate spin-valley polarized photocurrents along the edges.

Contribution

It introduces a general boundary condition framework for edge states in monolayer TMDs, incorporating edge spin-orbit interaction and predicting photocurrent polarization effects.

Findings

Edge states have linear dispersion determined by boundary parameters.

Absence of edge spin-orbit interaction simplifies the edge state spectrum.

Circularly polarized light induces spin and valley polarized photocurrents along edges.

Abstract

We develop an analytical theory for edge states in monolayers of transition metal dichalcogenides based on a general boundary condition for a two-band ${\bf kp}$-Hamiltonian in case of uncoupled valleys. Taking into account {\it edge} spin-orbit interaction we reveal that edge states, in general, have linear dispersion that is determined by three real phenomenological parameters in the boundary condition. In absence of the edge spin-orbit interaction, edge states are described by a single real parameter whose sign determines whether their spectra intersect the bulk gap or not. In the former case we show that illumination by circularly polarised light results in spin and valley polarised photocurrent along the edge. Flow direction, spin and valley polarisation of the edge photocurrent are determined by the direction of circular polarisation of the illuminated light.