Critical currents in the BEC-BCS crossover regime in an optical lattice

Both the trapping geometry and the interatomic interaction strength of a dilute ultracold fermionic gas can be well controlled experimentally. Adapting the interaction strength between the fermionic atoms allows tuning the gas from a molecular condensate to a Bardeen-Cooper-Schrieffer superfluid. We adopt a functional integral point of view to investigate how the superfluid properties vary during this crossover. In particular, the critical superfluid velocity for flowing through an optical lattice is derived. The observation of undamped motion in an optical lattice constitutes a hallmark of superfluidity, also in the fermionic systems. We discuss our theoretical results for the critical velocity of a fermionic superfluid in comparison to the experimental results for a bosonic superfluid in an optical lattice.