Two-level and three-level resonant measurements of impurity-bound magnetopolarons in multiple-quantum-well structures

Far-infrared photoconductivity has been used to follow the 1s-2p+ transition of shallow donors confined in GaAs/AlxGa1-xAs multiple-quantum-well structures through resonant regions with GaAs optical phonons by magnetic field tuning up to 23.5 T. Both two-level and three-level measurements show anti-level-crossing behavior with the lower branches far below (50 cm-1) the resonant energies for the bulk long-wavelength LO phonons, resulting in extremely large, asymmetric interaction gaps. The results strongly suggest that electrons interact with more than one set of phonons, or a phonon band. The electroninterface-phonon interaction provides a plausible explanation for the experimental observations.