Propagation of Sound in Two-Species Bose-Einstein Condensates
  We investigate the propagation of zero sound in two-species interpenetrating Bose-Einstein condensates. In very elongated clouds, this propagation is shown to be essentially one-dimensional. We also present 1D numerical experiments that exhibit the existence of two different sound pulses with velocities consistent with the theoretical predictions. 
D. Lima, P. Borckmans and G. Dewel