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: Univ Padua, Dipartimento Fis & Astron Galileo Galilei, Via Marzolo 8, I-35131 Padua, Italy; IST Austria Inst Sci & Technol Austria, Campus 1, A-3400 Klosterneuburg, Austria; Heidelberg Univ, Inst Theoret Phys, Philosophenweg 19, D-69120 Heidelberg, Germany; Consiglio Nazl Ric CNR, Ist Nazl Ott INO, Via Nello Carrara 1, I-50125 Sesto Fiorentino, Italy; Ist Nazl Fis Nucl INFN, Sez Padova, Via Marzolo 8, I-35131 Padua, Italy.

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.

Journal/Review: PHYSICAL REVIEW A

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

KeyWords: LIQUID-HELIUM; GAS; BCS
DOI: 10.1103/PhysRevA.103.L061303

ImpactFactor: 2.971
Citations: 8
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