Ten Years of Spin Hall Effect

In this short review I survey the theory of the spin Hall effect in doped semiconductors and metals in the light of recent experiments on both kinds of materials. After a brief introduction to different types of spin–orbit coupling in solids, I describe in detail the three conceptually distinct mechanisms that are known to contribute to the spin Hall effect, namely “skew-scattering”, “side-jump”, and “intrinsic mechanism”. The skew-scattering mechanism is shown to be dominant in certain clean two-dimensional semiconductors in which one component of the spin is conserved. In such systems the side-jump mechanism is sub-dominant, but universal in form, and can become dominant if the electron mobility is reduced by changing the temperature. Both skew-scattering and side-jump contributions are generally reduced by spin precession, and skew-scattering is completely suppressed in the linear Rashba model in the absence of magnetic field. Different models of spin–orbit coupling can, however, sustain an intrinsic spin Hall effect. A brief summary of the present experimental situation concludes the review.