Exciton Transport in Cu2O: Phonon Wind versus Superfluidity

Abstract

We focus on the recent experimental work by Mysyrowicz et al., in which nondiffusive transport of excitons in Cu2O was reported and attributed to Bose Einstein condensation of excitons. We discuss an alternate explanation of the macroscopic transport of excitons in Cu2O, its nonlinearity in case of two-pulse excitation, and the recently reported “exciton laser” effect under pulse and cw excitation. We show that these effects can be more reasonably attributed to the nonequilibrium phonon induced drag (“phonon wind”) and cannot be considered as experimental evidence of Bose Einstein condensation and superfluidity of excitons in Cu2O.