Nonlinearity of ultrafast anomalous Hall currents in GaAs

We induce ultrafast anomalous Hall currents in GaAs by above-bandgap optical femtosecond excitation at various temperatures, excitation energies and magnetic fields. The currents' dynamics is studied by detecting the simultaneously emitted THz radiation. A linear behavior is obtained at room temperature and low magnetic fields. However, at higher magnetic fields and both, room and low temperatures, we enter a highly nonlinear regime, in which the current dynamics drastically varies. Most likely, this variation results from different microscopic mechanisms which compete against each other.