Spin generation in a Rashba-type diffusive electron system by nonuniform driving field

We show that the Rashba spin-orbit interaction contributes to edge spin accumulation S(z) in a diffusive regime when the driving field is nonuniform. Specifically, we solve the case of nonuniform driving field in the vicinity of a circular void locating in a two-dimensional electron system and we identify the key physical process leading to the edge spin accumulation. The void has radius R(0) in the range of spin-relaxation length l(so) and is far from both source and drain electrodes. The key physical process we find is originated from the nonuniform in-plane spin polarizations. Their subsequent diffusive contribution to spin current provides the impetus for the edge spin accumulation S(z) at the void boundary. The edge spin accumulation is proportional to the Rashba coupling constant alpha and is in a spin-dipole form oriented transversely to the driving field. We expect similar spin accumulation to occur if the void is at the sample edge.