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 γ_S=0.12±0.04 is obtained for t_N=10nm at room temperature, while it is much smaller for the t_N=20nm sample. Combined ab initio and quantum Monte Carlo calculations for the skew scattering due to a Pt impurity show γ_S≅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.