Charge-to-spin conversion in twisted graphene/WSe$_2$ heterostructures

TL;DR

This study explores how the twist angle in graphene/WSe2 heterostructures influences charge-to-spin conversion efficiency, revealing optimal angles and novel effects driven by symmetry breaking, with implications for spintronic device design.

Contribution

First-principles analysis of twist angle effects on spin-orbit coupling and charge-to-spin conversion, uncovering optimal angles and unconventional Rashba-Edelstein effects in graphene/WSe2 heterostructures.

Findings

CSC efficiency peaks near 30° twist angle

Unconventional Rashba-Edelstein effect with spins collinear to electric field

Carrier doping controls crossover between Fermi-sea and surface spin responses

Abstract

We investigate the twist angle dependence of spin-orbit coupling (SOC) proximity effects and charge-to-spin conversion (CSC) in graphene/WSe$_2$ heterostructures from first principles. The CSC is shown to strongly depend on the twist angle, with both the spin Hall and standard Rashba-Edelstein efficiencies optimized at or near 30{\deg} twisting. Symmetry breaking due to twisting also gives rise to an unconventional Rashba-Edelstein effect, with electrically generated non-equilibrium spin densities possessing spins collinear to the applied electric field. We further discuss how the carrier doping concentration and band broadening control the crossover between the Fermi-sea and -surface spin response, which reconciles the seemingly disparate experimental observations of different CSC phenomena.