Superfluid transport of excitons in Cu2O

Experimental results concerning ballistic excitonic transport in high quality single crystals of cuprous oxide are presented and discussed. The onset conditions of this anomalous transport, in the form of a packet propagating at near sound velocity, is compatible with theoretical predictions for Bose-Einstein condensation of n = 1 paraexcitons. Experiments involving the interaction between two packets reveal coherence properties, in agreement with an interpretation assuming excitonic Bose-Einstein condensation Bs the origin of the packet. Amplification of the packet by thermal excitons is discussed in terms of radiationless exciton scattering induced by the condensate.