EXCITON TRANSPORT IN CU2O - PHONON WIND VERSUS SUPERFLUIDITY

We focus oil the recent experimental work by Mysyrowicz et al., in whi ch nondiffusive transport of excitons in Cu2O was reported and attribu ted to Bose Einstein condensation of excitons. We discuss an alternate explanation of the macroscopic transport of excitons in Cu2O, its non linearity in case of two-pulse excitation, and tile recently reported ''exciton laser'' effect under pulse and cw excitation. We show that t hese effects carl be more reasonably attributed to tile nonequilibrium phonon induced drag (''phonon wind'') and cannot be considered as exp erimental evidence of Bose Einstein condensation and superfluidity of excitons in Cu2O.