Spin polarization dynamics in a semiconductor microcavity

We have studied the spin dynamics of the polaritons in a GaAs/AlGaAs microcavity by means of polarization- and time-resolved photoluminescence spectroscopy as a function of excitation density and normal mode splitting. The experiments, performed under non-resonant excitation, revealed a novel behaviour of the polarization degree of the emission, which reaches its maximum at a finite time. We have also found that polariton stimulated emission takes place for excitation densities larger than 20 W/cm². This process has a strong influence on spin dynamics: the emission becomes almost completely polarized and negative values of the polarization are observed, whose magnitude depends on exciton-cavity detuning.