Quantum Degenerate Exciton-Polaritons in Thermal Equilibrium
  We study the momentum distribution and relaxation dynamics of semiconductor microcavity polaritons by angle-resolved and time-resolved spectroscopy. Above a critical pump level, the thermalization time of polaritons at positive detunings becomes shorter than their lifetime, and the polaritons form a quantum degenerate Bose-Einstein distribution in thermal equilibrium with the lattice. 
H Deng, D Press, S Gotzinger, GS Solomon, R Hey, KH Ploog, Y Yamamoto