Surface-assisted Spin Hall Effect in Au Films with Pt Impurities

We show, both experimentally and theoretically, a novel route to obtain giant room temperature spin Hall effect due to surface-assisted skew scattering. In the experiment, we report the spin Hall effect in Pt-doped Au films with different thicknesses $t_N$. The giant spin Hall angle $\gamma_S$ = $0.12 \pm 0.04$ is obtained for $t_N$ = 10 nm at room temperature, while it is much smaller for $t_N$ = 20 nm sample. Combined ab initio and quantum Monte Carlo calculations for the skew scattering due to a Pt impurity show $\gamma_S$ $\cong$ 0.1 on the Au (111) surface, while it is small in bulk Au. The quantum Monte Carlo results show that the spin-orbit interaction of the Pt impurity on the Au (111) surface is enhanced, because the Pt 5d levels are lifted to the Fermi level due to the valence fluctuation. In addition, there are two spin-orbit interaction channels on the Au (111) surface, while only one in bulk Au.