Frictionless flow in a binary polariton superfluid
  We study the properties of a binary microcavity polariton superfluid coherently injected by two lasers. The crossover from the supersonic to subsonic regime, where motion is frictionless, is described by evaluating the Bogoliubov spectra. We show that according to the Landau criteria, the coupling between the two components precludes the existence of superfluidity just for one component but not for the other. By analysing the drag force exerted on a defect, we give a recipe to experimentally address the crossover from the supersonic to the subsonic regime. 
E. Cancellieri, F. M. Marchetti, M. H. Szymanska, D. Sanvitto, and C.   Tejedor
cond-mat.mes-hall cond-mat.quant-gas