Observation of Coupling of Excitons with Free Electron in Light Scattering from GaAs Quantum Wells.

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