  Electrons in double-layer semiconductor heterostructures experience a special
type of spin-orbit interaction which arises in each layer from the
perpendicular component of the Coulomb electric field created by electron
density fluctuations in the other layer. We show that this interaction, acting
in combination with the usual spin-orbit interaction, can generate a spin
current in one layer when a charge current is driven in the other. This effect
is symmetry-wise distinct from the spin Hall drag. The spin current is not, in
general, perpendicular to the drive current.
