Signature of the microcavity exciton-polariton relaxation mechanism in the polarization of emitted light

We have performed real and momentum space spin-dependent spectroscopies of spontaneously formed exciton polariton condensates for a nonresonant pumping scheme. Under a linearly polarized pump, our results can be understood in terms of spin-dependent Boltzmann equations in a two-state model. This suggests that relaxation into the ground state occurs after multiple phonon-scattering events and only one polariton-polariton scattering. For the circular pumping case, in which only excitons of one spin are injected, a bottleneck effect is observed, implying inefficient relaxation.