Detection of the anomalous velocity and anomalous Hall effect in GaAs via free-space THz spectroscopy

The anomalous velocity causes spin-polarized carriers to move perpendicular to an electric or parallel to a magnetic driving field. It is at the origin of the spin Hall and anomalous Hall effects. Here, we employ time-domain THz spectroscopy to study the anomalous velocity and the anomalous Hall effect, both of which are optically induced in GaAs, on a sub-picosecond time scale. Our results not only enable a distinction between intrinsic (Berry curvature) and extrinsic (scattering) effects but also demonstrate an inversion of anomalous Hall currents versus excitation photon energy.