Coupling of excitons with free electrons in light scattering from GaAs quantum wells

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Abstract
We observe unexpectedly narrow peaks (∼1–2 meV) in the resonant enhancement of inelastic light scattering by a two-dimensional electron gas. The experiments are carried out in high-mobility modulation-doped GaAs quantum wells. Scattering by spin-density and charge-density intersubband excitations is enhanced through incoming and outgoing channels. Such excitonic resonances are much sharper than the Fermi energy (10–20 meV). To explain these observations we propose new mechanisms for light scattering by excitations of the electron gas. They are based on the coupling between excitons and the Fermi sea through Coulomb exchange and direct interactions.