Theory of spin injection in two-dimensional metals with proximity-induced spin-orbit coupling

Spin injection is a powerful experimental probe into a wealth of nonequilibrium spin-dependent phenomena displayed by materials with sizable spin-orbit interactions. Here, we present a theory of coupled spin-charge diffusive transport in spin-valve devices built from two-dimensional materials. The formalism takes into account realistic spin-orbit effects with both spatially uniform and random components in van der Waals materials arising from the interfacial breaking of inversion symmetry. The various charge-to-spin conversion mechanisms known to be present in diffusive metals, including the spin Hall effect and several mechanisms contributing to current-induced spin polarization are accounted for. Our analysis shows that the dominant conversion mechanisms can be discerned by analyzing the nonlocal resistance of the spin valve for different polarizations of the injected spins and as a function of the applied in-plane magnetic field.