Spin generation away from boundaries by nonlinear transport

Spin polarization may be generated far from the boundaries of a sample by nonlinear effects of an electric current, in the presence of "extrinsic" spin-orbit interactions, even when such generation is forbidden in the linear regime. We present a Corbino model where spin accumulation results from a combination of current gradients, nonlinearity, and cubic anisotropy. Further, we show that even with isotropic conductivity, nonlinear effects in a low-symmetry sidearm geometry can generate spin polarization far away from boundaries. Finally, we find that drift from the boundaries dominates spin polarization patterns observed in recent experiments on GaAs by Sih et al. [ Phys. Rev. Lett. 97 096605 (2006)].