Landau-Level Signatures in Ultrafast Anomalous Hall Currents at Room Temperature

We study ultrafast anomalous Hall currents in bulk GaAs generated using optical femtosecond excitation and magnetic fields up to 7 T. The currents’ dynamics are resolved by measuring the simultaneously emitted THz radiation. The resulting current amplitude shows maxima at excitation photon energies, which agree well with interband transitions between valence and conduction band Landau levels. This behavior is observed for both cryogenic and room temperature. While our work helps to better understand the anomalous Hall effect, it also demonstrates a method to detect and possibly employ Landau levels at elevated temperatures.