Ortho-exciton polariton relaxation by phonon scattering in Cu2O

The Boltzmann relaxation kinetics of ortho-excitons by scattering with ther mal acoustic phonons is treated, taking into account the weak polariton eff ect due to the quadrupole-allowed optical transitions. The relatively small polariton splitting is shown to be sufficient to allow a decay of the uppe r-branch polaritons into the states on the lower branch. Because of this de cay, the Bose-Einstein condensation in the k = 0 state of the upper-branch polaritons is, even without other finite lifetime effects, only a transient phenomenon. (C) 2000 Elsevier Science Ltd. All rights reserved.