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

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. {\bf 124}, 240403 (2020)] 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.

arXiv comment6 pages, 3 figures; published version, correction of journal reference

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Cited by in corpus (9)

• Observation of superfluidity in a strongly correlated two-dimensional Fermi gas
• Shell-shaped atomic gases
• Second sound with ultracold atoms: A brief historical account
• Berezinskii-Kosterlitz-Thouless phase transition with Rabi-coupled bosons
• Unitary Fermi superfluid near the critical temperature: thermodynamics and sound modes from elementary excitations
• First and second sound in a dilute Bose gas across the BKT transition
• Mechanism for sound dissipation in a two-dimensional degenerate Fermi gas
• Predictive power of the Berezinskii-Kosterlitz-Thouless theory based on Renormalization Group throughout the BCS-BEC crossover in 2D superconductors
• First and second sound in two-dimensional bosonic and fermionic superfluids