Probing the magnetic field dependence of the light hole transition in GaAs/AlGaAs quantum wells using optically pumped NMR

Optically pumped NMR (OPNMR) of the NMR-active $^69/71\mathrm{Ga}$ species has been shown to be a unique method to probe electronic energy bands in GaAs, with sensitivity to the light hole--to--conduction band transition. This transition is often obscured in other optical measurements such as magnetoabsorption. Using OPNMR, we exploit the hyperfine interaction between conduction band electrons (and their spin states) and nuclear spins, which are detected through phase-sensitive radio-frequency (NMR) spectroscopy. Measurements were made over a range of external magnetic fields (${B}₀$) in two different labs with separate experimental setups to obtain the magnetic field dependence of the light hole--to--conduction band transition energy. In addition, $k\ifmmode\cdot\else\textperiodcentered\fi{}p$ theory was used to interpret the experimental results, mapping out this specific transition's magnetic field dependence in an AlGaAs/GaAs quantum well. The combination of theory and experiment point to a mixing of valence bands at a field of approximately ${B}₀=4.7$ T, swapping the dominant character of the absorption transition and, thus, explaining the magnetic field dependence. Lastly, the experimental dependence of the light hole--to--conduction band transition energy on ${B}₀$ is found to be less steep compared to the calculated trend, indicating that inclusion of additional effects may be necessary to accurately model the spin-split band structure. The additional insight gained by $^69/71\mathrm{Ga}$ OPNMR about the light hole states will facilitate future testing of more complex band structure models.