Spin-Hall effect in a disordered 2D electron-system

We calculate the spin-Hall conductivity for a two-dimensional electron gas within the self-consistent Born approximation, varying the strength and type of disorder. In the weak disorder limit we find both analytically and numerically a vanishing spin-Hall conductivity even when we allow a momentum dependent scattering. Separating the reactive from the disspative current response, we find the universal value $\sigma^R_{sH} = e/8 \pi$ for the reactive response, which cancels however with the dissipative part $\sigma^D_{sH} = -e/8 \pi$.