Spin current and polarization in impure 2D electron systems with   spin-orbit coupling
  We derive the transport equations for two-dimensional electron systems with spin-orbit interaction and short-range spin-independent disorder. In the limit of slow spatial variations of the electron distribution we obtain coupled diffusion equations for the electron density and spin. Using these equations we calculate electric-field induced spin accumulation in a finite-size sample for arbitrary ratio between spin-orbit energy splitting and elastic scattering rate. We demonstrate that the spin-Hall conductivity vanishes in an infinite system independent of this ratio. 
E.G. Mishchenko, A.V. Shytov, and B.I. Halperin