Transport Equations and Spin-Charge Propagating Mode in the Two   Dimensional Hole Gas
  We find that the spin-charge motion in a strongly confined two-dimensional hole gas (2DHG) supports a propagating mode of cubic dispersion apart from the diffusive mode due to momentum scattering. Propagating modes seem to be a generic property of systems with spin-orbit coupling. Through a rigorous Keldysh approach, we obtain the transport equations for the 2DHG, we analyze the behavior of the hole spin relaxation time, the diffusion coefficients, and the spin-charge coupled motion. 
Taylor L. Hughes, B. Andrei Bernevig, and Yaroslaw B. Bazaliy