Twist-Tunable Spin-to-Charge Conversion and Valley-Contrasting Effects in Graphene/TMDC Heterostructures

TL;DR

This paper investigates how twisting graphene on TMDC monolayers affects spin-to-charge conversion and valley effects, revealing tunable and quantized valley Hall conductivity dependent on the twist angle.

Contribution

It introduces an effective model to analyze twist-angle-dependent spin-orbital and valley phenomena in graphene/TMDC heterostructures, with analytical formulas for key effects.

Findings

Valley Hall conductivity can be quantized at ±2 e^2/h.

Spin Hall effect and spin polarization depend on twist angle.

Proximity-induced effects are tunable via twist angle.

Abstract

We consider graphene deposited on monolayers of such transition-metal dichalcogenides like MoSe$_2$, WSe$_2$, MoS$_2$, and WS$_2$. Our key objective is to study the impact of relative twist angle between the monolayers on the proximity-induced spin-orbital effects and orbital phenomena in graphene. To do this we used an effective model Hamiltonian for low-energy states, taken from available literature. The Green function formalism is used to calculate analytical formula for the spin Hall effect and nonequilibrium spin polarization in the system. We also determine the valley Hall and valley polarization effects, and their dependence on the twist angle. We have shown that the valley Hall conductivity can take the quantized value equal to $\pm 2 e^2/h$.