Pure Out-of-Plane Spin Polarization Induced by Rashba-Type Splitting

The generation of out-of-plane polarized spin currents presents a significant challenge in field-free spintronics. Traditional Rashba-type spin splitting typically generates in-plane spin currents, thereby limiting the development of high-density perpendicular magnetic memory and logic devices. Using first-principles calculations, we predict the emergence of pure out-of-plane Rashba-type spin splitting in monolayer transition metal dichalcogenides (TMDs). The momentum-dependent effective magnetic field governs both the direction of spin polarization and the form of spin splitting in the TMDs. Due to the presence of nonzero Berry curvature, this system holds promise for generating a purely out-of-plane polarized spin current, a phenomenon that may extend to other materials with broken in-plane symmetry.