Spin-Hall effect and spin-coherent excitations in a strongly confined two-dimensional hole gas

Based on a rigorous quantum-kinetic approach, spin-charge coupled drift-diffusion equations are derived for a strongly confined two-dimensional hole gas. An electric field leads to a coupling between the spin and charge degrees of freedom. For weak spin-orbit interaction, this coupling gives rise to the intrinsic spin-Hall effect. There exists a threshold value of the spin-orbit coupling constant that separates spin diffusion from ballistic spin transport. In the latter regime, undamped spin-coherent oscillations are observed. This result is confirmed by an exact microscopic approach valid in the ballistic regime.