Role of excitons in double Raman resonances in GaAs quantum wells

Raman scattering by longitudinal-optical phonons has been measured in GaAs-AlAs multiple quantum wells at high magnetic fields. Doubly resonant scattering processes are observed at photon energies corresponding to magneto-excitons with different principal quantum numbers for the incoming and outgoing channels. The existence of these initially forbidden scattering processes, their resonance energies, and their relative intensities are correctly reproduced by our theoretical description. The model takes into account the excitonic nature of the intermediate states, as well as scattering processes involving a nonzero in-plane phonon wave vector, which is required to allow inter-Landau level sca…