Hydrostatic pressure dependence of negative-donor-ion singlet and singlet-like bound magnetoplasmon transitions in doped GaAs/AlGaAs quantum wells

Applied hydrostatic pressure modifies the Coulomb bound states of a quasi-two-dimensional electron gas in quantum wells by increasing the effective mass and by tuning the free electron density. Here, we explore these mechanisms by measuring the effects of pressure on the cyclotron resonance, the D⁰ 1s→2p⁺ transition, and the D^--singlet and singlet-like transitions in low-and high-density, modulation-doped GaAs quantum wells. For low doping density, detailed calculations employing a pressure-dependent electron mass agree well with the observed magnetic field and pressure dependencies. For high doping density and low fields, the blue-shift of the D^--singlet-like transition at fields below 8 T decreases with applied pressure as anticipated, due to loss of free electrons via the Γ-X crossover. However, near approximately 7.5 T, this singlet-like transition exhibits an anomalous branching for pressures above 4 kbar, which indicates the presence of a resonant level and obscures the blue-shift at high fields.