Sign change of spin Hall effect due to electron correlation in CuIr alloys

Recently the predominant extrinsic skew scattering mechanism with a positive spin Hall angle (SHA) was experimentally observed in nonmagnetic CuIr alloys [Niimi et al., Phys. Rev. Lett. 106, 126601 (2011)], while the negative SHA was obtained by ab initio simulation if the consistent definition of SHA is used [Fedorov et al., Phys. Rev. B 88, 085116 (2013)]. We reconsider the SHA in CuIr alloys by the quantum Monte Carlo method, where the Coulomb correlation U in 5d orbitals of Ir impurities is properly included. It indicates that the SHA is negative without electron correlation (U=0), and becomes positive when an electron correlation of U=0.5 eV is included, which is consistent with the experiment. It opens a way to control the sign of SHA by electron correlation in novel spintronic devices.