Dynamics associated with Bose-Einstein statistics of orthoexcitons generated by resonant excitations in cuprous oxide

Orthoexcitonic gas in cuprous oxide is generated by one and two photon resonant excitations at different excitation intensities and at different temperatures between 1.8 and 4.2 K. The experimental results are analyzed by simulation with a Boltzmann equation. When the exciton density is low, the observed luminescence is found to originate from a nonequilibrium excitonic gas where the exciton-LA phonon scattering dominates. When the exciton density is very high, not only the exciton-LA phonon scattering but also the exciton-exciton scattering is important. The observed luminescence consists of two systems: one is from an exciton system that is distributed according to the usual Bose-Einstein statistics with chemical potential mu=0, while the other is from excitons with zero kinetic energy. The two systems were found to be in thermal equilibrium. The latter system might be a form of Bose-Einstein condensation.