Charge-to-Spin Interconversion in Low-Symmetry Topological Materials

We theoretically show that the reduced symmetry of strong spin-orbit coupling materials such as MoTe₂ or WTe₂ enables a new form of oblique spin Hall effect (SHE), characterized by large and robust in-plane spin polarizations. Through quantum transport calculations on realistic device geometries, including disorder, we found long spin diffusion lengths (λ_s) and a gate tunable charge-to-spin interconversion efficiency with an upper value reaching θ_xy ∼ 80%. The SHE figure of merit λ_sθ_xy ∼ 1-50 nm, can significantly exceed values of conventional SHE materials, and stems from momentum invariant (persistent) spin textures together with large spin Berry curvature along the Fermi contour. Specific guidelines for unambiguous experimental confirmation are proposed, paving the way towards exploiting such phenomena in spintronic devices.