Twist Angle-Dependent Spin-Orbit Proximity Effects and Charge-to-Spin Conversion in graphene/WSe₂ Heterostructures

The spin-orbit coupling (SOC) proximity effects of transition-metal dichalcogenides (TMDC) to graphene enrich the spin texture of Dirac states of graphene and thus lead to intriguing charge-to-spin conversion (CSC). Based on first-principles calculations and linear response theory, we investigate the twist angle dependence of proximity effects and charge-to-spin conversion (CSC) in graphene/WSe₂ heterostructures. We found that both Rashba and valley-Zeeman SOCs strongly depend on the twist angle, and the induced staggered potential and the valley-Zeeman SOC are fully suppressed with 30° twisting due to symmetry constraints. As a result, the disorder-free spin Hall and Rashba-Edelstein CSC efficiencies are also shown to strongly depend on the twist angle, being simultaneously optimized near 30° twisting. In addition, symmetry breaking due to twisting gives rise to a novel unconventional Rashba-Edelstein effect, with non-equilibrium spin densities possessing spins parallel to the electric field direction. Our findings offer a new perspective on the spintronics of graphene/WSe₂ systems, opening up opportunities for efficient control of CSC in Van der Waals heterostructures.