Exciton-phonon droplets with Bose-Einstein condensate: transport and   optical properties
  We discuss the possibility for a moving droplet of excitons and phonons to form a coherent state inside the packet. We describe such an inhomogeneous state in terms of Bose-Einstein condensation and prescribe it a macroscopic wave function. Existence and, thus, coherency of the Bose-core inside the droplet can be checked experimentally by letting two moving packets to interact. 
D. Roubtsov (U. of Montreal), Y. Lepine, I. Loutsenko