Propagation of sound in density modulated superfluids
Sandro Stringari (Pitaevskii BEC Center, Universita di Trento)
I will discuss the propagation of sound in superfluid quantum gases breaking translational invariance. I will consider both the case of a quantum gas subject to an external periodic potential and the case where translational symmetry is broken in a spontaneous way, giving rise to supersolidity. The role of the superfluid density in determining the sound velocity at zero temperature is explicitly pointed out in both cases.