Propagation of first and second sound in a two-dimensional Fermi superfluid

Year: 2021

Authors: Tononi A.; Cappellaro A.; Bighin G.; Salasnich L.

Autors Affiliation: Dipartimento di Fisica e Astronomia “”Galileo Galilei,”” Universita di Padova, via Marzolo 8, 35131 Padova, Italy; IST Austria (Institute of Science and Technology Austria), Am Campus 1, 3400 Klosterneuburg, Austria; Institut f

Abstract: Sound propagation is a macroscopic manifestation of the interplay between the equilibrium thermodynamics and the dynamical transport properties of fluids. Here, for a two-dimensional system of ultracold fermions, we calculate the first and second sound velocities across the whole BCS-BEC crossover, and we analyze the system response to an external perturbation. In the low-temperature regime we reproduce the recent measurements [Phys. Rev. Lett. 124, 240403 (2020)PRLTAO0031-900710.1103/PhysRevLett.124.240403] of the first sound velocity, which, due to the decoupling of density and entropy fluctuations, is the sole mode excited by a density probe. Conversely, a heat perturbation excites only the second sound, which, being sensitive to the superfluid depletion, vanishes in the deep BCS regime and jumps discontinuously to zero at the Berezinskii-Kosterlitz-Thouless superfluid transition. A mixing between the modes occurs only in the finite-temperature BEC regime, where our theory converges to the purely bosonic results.


Volume: 103 (6)      Pages from: L061303-1  to: L061303-6

DOI: 10.1103/PhysRevA.103.L061303