Exciton transport in Cu2O

The low temperature exciton transport in Cu2O shows a transition from a dif fusive to sonic ballistic regime with increase of excitation power or decre ase of temperature, and also well pronounced nonlinearities under two-pulse and under pulse plus cw excitation. These features have been interpreted b y the authors of the experiments as a proof of Bose-Einstein condensation ( BEC) in the exciton system and its superfluidity. However, we have shown pr eviously that most of these transport phenomena in Cu2O can be quantitative ly explained within the nonequilibrium phonon-assisted (phonon wind) model, whereas the superfluid interpretation meets multiple inconsistencies. In t he present paper we show that the recent experiments by the same group with spatially separated and/or time delayed two-pulse excitation are as well f ully explained by the phonon wind picture.