Stability of superfluid Fermi gases in optical lattices

TL;DR

This paper theoretically investigates the stability of superfluid Fermi gases in optical lattices, revealing that roton-like excitations lead to destabilization before pair breaking occurs, across the BCS-BEC crossover.

Contribution

It introduces the analysis of roton-like Anderson-Bogoliubov modes as a destabilization mechanism in superfluid Fermi gases within optical lattices.

Findings

Roton-like minima in AB mode spectrum reach zero before single-particle spectrum.

Superfluid destabilization occurs via roton emission, not Cooper pair breaking.

Destabilization mechanism is consistent across BCS-BEC crossover.

Abstract

Critical velocities of superfluid Fermi gases in optical lattices are theoretically investigated across the BCS-BEC crossover. We calculate the excitation spectra in the presence of a superfluid flow in one- and two-dimensional optical lattices. It is found that the spectrum of low-lying Anderson-Bogoliubov (AB) mode exhibits a roton-like structure in the short-wavelength region due to the strong charge density wave fluctuations, and with increasing the superfluid velocity one of the roton-like minima reaches zero before the single-particle spectrum does. This means that superfluid Fermi gases in optical lattices are destabilized due to spontaneous emission of the roton-like AB mode instead of due to Cooper pair breaking.