Observation of Terahertz Spin Hall Conductivity Spectrum in Bulk GaAs at Room Temperature

We investigated ultrafast dynamics of light-induced anomalous Hall conductivity in a bulk semiconductor GaAs at room temperature using a circularly polarized near-infrared pump pulse and a terahertz (THz) probe pulse. Polarization rotation of the THz pulse was observed as a manifestation of the inverse spin Hall effect (ISHE) for optically injected spin-polarized carriers. The spin Hall conductivity spectrum is experimentally evaluated for the first time and shows excellent agreement with the microscopic theories of ISHE, demonstrating that the extrinsic impurity scattering dominates ISHE in the DC limit, whereas the intrinsic Berry-curvature mechanism becomes dominant for THz frequency. Our study paves a way toward ultrafast study of spin Hall effect with quantitative analysis of spin Hall conductivity spectrum.