Faraday waves in strongly interacting superfluids

Abstract

We report on the observation of Faraday waves in a cigar-shaped Fermi superfluid of 6Li parametrically excited by modulating the radial trap frequency. We characterize the phenomenon as a function of the interaction parameter employing a Feshbach resonance. Starting from the BEC side of the resonance, we observe a reduction of visibility of the Faraday pattern as we approach unitarity, possibly due to the increased incompressibility of the system. We probe the superfluid excitation spectrum by extracting an effective 1D speed of sound for different values of the interaction parameter, in good agreement with numerical simulations. We also discuss the effects introduced by the finite size of the sample. Finally, we introduce a novel model based on Floquet theory that we employ to perform a stability analysis in the parameter space, showing the emergence of the Faraday waves as unstable solutions to a Mathieu-like equation.