Polarized interacting exciton gas in quantum wells and bulk semiconductors.

We develop a theory to calculate exciton binding energies of both two-and three-dimensional spin polarized exciton gases within a mean field approach. Our method allows the analysis of recent experiments showing the importance of the polarization and intensity of the excitation light on the exciton lumines-cence of GaAs quantum wells. We study the breaking of the spin degeneracy observed at high exciton density (5 10 10 cm 2). Energy level splitting betwen spin +1 and spin-1 is shown to be due to many-body inter-excitonic exchange while the spin relaxation time is controlled by intra-exciton exchange.