Nonexistence of intrinsic spin currents
  We have described the electron spin dynamics in the presence of the spin-orbit interaction and disorder using the spin-density matrix method. We showed that in the Born approximation in the scattering amplitude the spin current is zero for an arbitrary ratio of the spin-orbit splitting and the scattering rate. Various types of the disorder potential are studied. We argue that the bulk spin current has always an {\it extrinsic} nature and depends explicitely on scattering by impurities since it appears only beyond the Born approximation in the scattering amplitude. 
Alexander Khaetskii