Pure spin currents induced by spin-dependent scattering processes in   SiGe quantum well structures
  We show that spin-dependent electron-phonon interaction in the energy relaxation of a two-dimensional electron gas results in equal and oppositely directed currents in the spin-up and spin-down subbands yielding a pure spin current. In our experiments on SiGe heterostructures the pure spin current is converted into an electric current applying a magnetic field that lifts the cancellation of the two partial charge flows. A microscopic theory of this effect, taking account of the asymmetry of the relaxation process, is developed being in a good agreement with the experimental data. 
S.D. Ganichev, S.N. Danilov, V.V. Bel'kov, S. Giglberger, S.A.   Tarasenko, E.L. Ivchenko, D. Weiss, W. Jantsch, F. Schaeffl...