Magnetic- and electric-field-induced anomalous Hall currents from optical excitation of Landau transitions in bulk GaAs

TL;DR

This study investigates anomalous Hall currents in bulk GaAs induced by optical excitation of Landau levels under magnetic and electric fields, revealing discrete features and Berry-phase effects at room temperature.

Contribution

It demonstrates room-temperature detection of Landau level transitions and links Berry-phase effects to anomalous Hall currents in GaAs, using ultrafast optical and THz measurements.

Findings

Detection of Landau band transitions at room temperature.

Distinct THz spectral features linked to Berry-phase effects.

Electron and hole dynamics contribute to complex current behavior.

Abstract

We study a certain type of anomalous Hall current in magnetically- and electrically-biased bulk GaAs samples under the formation of Landau levels. The currents are generated by ultrafast optical excitation of spin-polarized carriers and detected by time-resolved measurements of the simultaneously emitted THz radiation. Due to the requirements of simultaneous magnetic and electric driving fields we refer to these currents as BE-AHC. We find that the BE-AHC peak for optical transitions between the band extrema of Landau levels of valance and conduction bands. These discrete features are attributed to the energy dependence of the geometric phases being responsible for anomalous transport effects in a semiconductor bandstructure. Surprisingly, we even detect the discrete Landau band transitions at room temperature, most likely due to the ultrafast local probing realized in our experiment. An analysis of the THz spectra using a model, based on the Boltzmann transport equation of optically excited carriers, shows that electron and hole contributions lead to complex current dynamics. While the cyclotronic motion of electrons results in a dip in the THz spectral response of BE-AHC, it causes a peak in the spectral response of normal Hall currents. Additionally, our experimental results strongly suggest that the Landau levels of the valance band play a significant role in the generation of BE-AHC. We expect that our results will initiate further studies on Berry-phase effects in Landau bands.