Signature of the microcavity exciton-polariton relaxation mechanism in   the polarization of emitted light
  We have performed real and momentum space spin-dependent spectroscopy of spontaneously formed exciton polariton condensates for a non-resonant pumping scheme. Under 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. 
Georgios Roumpos, Chih-Wei Lai, T. C. H. Liew, Yuri G. Rubo, A. V.   Kavokin, and Yoshihisa Yamamoto