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

The spin polarization induced by the spin Hall effect (SHE) in thin films typically points out of the plane. This is rooted on the specific symmetries of traditionally studied systems, not in a fundamental constraint. Here, we show that the reduced symmetry of strong spin-orbit coupling materials such as MoTe2 or WTe2 enables a new form of canted spin Hall effect (SHE), characterized by large and robust in-plane spin polarizations, which gives rise to an unprecedented charge-to-spin interconversion effect. Through quantum transport calculations on realistic device geometries, including disorder, we found long spin diffusion lengths (λs) and a gate tunable charge-to-spin interconversion efficiency with an upper value reaching θxy ≈ 80%. The SHE figure of merit λsθxy ∼ 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. These findings vividly emphasize how crystal symmetry and band topology can govern the intrinsic SHE, and how they may be exploited to broaden the range and efficiency of spintronic functionalities.