Enhanced spin Hall effect by resonant skew scattering in orbital-selective Kondo effect

The enhanced spin Hall effect in Au metal due to the resonant skew scattering is studied with first-principles band structure calculations. Especially the gigantic spin Hall angle ${\gamma }_S\cong 0.1$ observed recently (T.Seki et al., Nature Materials {\bf 7}, 125 (2008)) is attributed to the orbital-dependent Kondo effect of Fe in the Au host metal, where the $t_{2g}$-orbitals are in the mixed-valence region while $e_g$-orbitals are in the Kondo limit. The enhanced spin-orbit interaction by the electron correlation in the $t_{2g}$-orbitals leads to the gigantic spin Hall effect. Impurities with 5d orbitals are also discussed.