Effects of periodic potentials on the critical velocity of superfluid Fermi gases in the BCS-BEC crossover

TL;DR

This paper investigates how a 1D optical lattice influences the critical velocity of superfluid Fermi gases across the BCS-BEC crossover, revealing reduced pair-breaking effects and non-monotonic behavior of critical velocity.

Contribution

It provides a detailed numerical analysis of the impact of periodic potentials on superfluid Fermi gases, highlighting new effects on pair-breaking and phonon excitations across the crossover.

Findings

Periodic potential reduces pair-breaking excitations when recoil energy is comparable to Fermi energy.

Strong lattice height leads to tightly bound pairs, suppressing pair-breaking in the BCS regime.

Critical velocity exhibits non-monotonic behavior along the BCS-BEC crossover when recoil energy is high.

Abstract

We study the effects of an external periodic potential on the critical velocity of a superfluid Fermi gas in the crossover between the Bardeen-Cooper-Schrieffer (BCS) phase and Bose-Einstein condensation (BEC). We numerically solve the Bogoliubov-de Gennes equations to model a three-dimensional (3D) gas of ultracold atoms in the superfluid phase flowing through a 1D optical lattice. We find that when the recoil energy is comparable to the Fermi energy, the presence of the periodic potential reduces the effect of pair-breaking excitations. This behavior is a consequence of the peculiar band structure of the quasiparticle energy spectrum in the lattice. When the lattice height is much larger than the Fermi energy, the periodic potential makes pairs of atoms to be strongly bound even in the BCS regime and pair-breaking excitations are further suppressed. We have also found that when the recoil energy is comparable to or larger than the Fermi energy, the critical velocity due to long-wavelength phonon excitations shows a non-monotonic behavior along the BCS-BEC crossover.