Search for the mechanism of the spin Hall effect

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We have studied extrinsic spin Hall effect(SHE) in Cu-based alloys. Copper has a very weak spin-orbit(SO) interaction and the SHE of Cu itself is negligibly small. However, by adding impurities with strong SO interactions such as Ir and Bi, the extrinsic SHEs can be generated. Unlike pure SHE materials such as Pt and Pd, one of the big advantages for the extrinsic SHE is that it allows controlling the SH angle, characteristic of the conversion yield between charge and spin, by changing the combination of host and impurity metals as well as by tuning the impurity concentration. By doping with Ir impurities, we observe a clear SHE signal. From the slope of the SH resistivity as a function of doping concentration, we estimate the SH angle to be 2%. When Ir impurities are replaced by Bi ones, the obtained SH angle is more than one order larger than that of CuIr alloys.