Superfluid Fraction and Leggett Bound in a Density Modulated Strongly Interacting Fermi Gas at Zero Temperature

Abstract

We calculate the superfluid fraction of an interacting Fermi gas, in the presence of a one-dimensional periodic potential of strength $V_0$ and wave-vector $q$. Special focus is given to the unitary Fermi gas, characterized by the divergent behavior of the s-wave scattering length. Comparison with the Leggett's upper bound $(⟨n_{1D}⟩<1/n_{1D}>{)}^{-1}$, with $n_{1D}$ the 1D column density, explicitly shows that, differently from the case of a dilute interacting Bose gas, the bound significantly overestimates the value of the superfluid fraction, except in the phonon regime of small $q$. Sum rule arguments show that the combined knowledge of the Leggett bound and of the actual value of the superfluid fraction allows for the determination of curvature effects providing the deviation of the dispersion of the Anderson-Bogoliubov mode from the linear phonon dependence. The comparison with the predictions of the weakly interacting BCS Fermi gas points out the crucial role of two-body interactions. The implications of our predictions on the anisotropic behavior of the sound velocity are also discussed.

10 pages, 3 figures

References in corpus (4)

• General coordinate invariance and conformal invariance in nonrelativistic physics: Unitary Fermi gas
• Excitation Spectrum and Superfluid Gap of an Ultracold Fermi Gas
• Superfluid fraction in an interacting spatially modulated Bose-Einstein condensate
• Equation of state and effective mass of the unitary Fermi gas in a 1D periodic potential

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• Superfluid Fraction of a 2D Bose-Einstein Condensate in a Triangular Lattice
• Probing Superfluidity with Quantum Vortex Necklaces
• Impurity-controlled vortex mobility and pair-breaking in fermionic superfluid rings