Collisions between supercooled excitons in Cu2O studied by time-resolved Lyman spectroscopy

Abstract : Supercooled orthoexcitons are generated in Cu2O by resonant two-photon excitation with a femtosecond laser pulse. The excitonic Lyman series is systematically analyzed by time-resolved induced-absorption measurements. The decay time of orthoexcitons as well as the buildup and decay times of paraexcitons are found to be dependent on their respective densities. With these results, the two-body excitonic spin-exchange and the exciton dissociation processes are investigated. The collision-induced spin-exchange process is found to dominate in the early stage of photoexcitation. The conditions required to obtain a Bose-Einstein condensate with paraexcitons are discussed.