Three Sound Modes in a Bose–Fermi Superfluid Mixture at Finite Temperatures

Abstract

We study sound propagation in a Bose Fermi superfluid mixture at finite temperatures. Sound modes in the mixture are described by the extended Landau's hydrodynamic theory. Our extended Landau's hydrodynamic theory shows that three sound modes exist. We calculate the hydrodynamic sound velocities and weights in the density response function based on the approach of Nozieres and Schmitt-Rink for the BCS to Bose-Einstein condensation crossover. In a Bose-Fermi superfluid mixture, the three sound mode pulses can be excited with an appreciable amplitude by density perturbations.