  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.
