Séminaire du LPTMS : Luca Salasnich (Padua University)

Superfluid thermodynamics of the unitary Fermi gas

Luca Salasnich (Padua University)

Hybrid: onsite seminar + zoom.

We investigate the superfluid thermodynamics of the unitary Fermi gas by introducing a model based on the
zero-temperature spectra of both bosonic collective modes and fermionic single-particle excitations.
We calculate the Helmholtz free energy and from it we obtain the entropy, the internal energy and
the chemical potential as a function of the temperature. By using these quantities and the Landau’s
expression for the superfluid density we determine analytically the superfluid fraction, the critical
temperature, the first sound velocity and the second sound velocity. We compare recent
experimental results [Science 375, 528 (2022)] of the superfluid unitary Fermi gas near the critical
temperature with our model. We find very good agreement between experimental data and our
theory for several quantities such as first sound, second sound, and superfluid fraction. We also
show that mode mixing between first and second sound occurs. Finally, we characterize the
response amplitude to a density perturbation: close to the critical temperature both first and second
sound can be excited through a density perturbation, whereas at lower temperatures only the first
sound mode exhibits a significant response.

Date/Time : 30/05/2023 - 11:00 - 12:00

Location : Salle des séminaires du FAST et du LPTMS, bâtiment Pascal n°530