Double Raman Resonances in Semiconductor Multiquantum Wells Induced by High Magnetic Fields

Raman resonance profiles have been measured in GaAs/AlAs multiple-quantum wells (MQW) under magnetic fields up to 20T both for (100) and (111) crystal orientations. The intensity of the resonance increases by several orders of magnitude when the energy difference between two magneto-exciton states, acting as incoming and outgoing channels, respectively, equals the GaAs LO phonon frequency. The results are interpreted as double Raman resonances involving both light-hole (Ln) and heavy-hole (Hn) magnetoexcitons as intermediate states in the scattering process. Double resonances have been observed at precise values of the magnetic field and excitation wavelength for different polarization configurations in both crystal orientations. Our results strongly suggest that the intermediate states in the Raman process are excitons rather than decoupled electrons and/or holes.