Critical currents in the BEC/BCS crossover regime

TL;DR

This paper explores the transition between BCS superfluidity and Bose-Einstein condensation in ultracold fermionic gases, analyzing critical currents and superfluid properties across the crossover using a functional integral approach.

Contribution

It provides a theoretical framework describing both BCS and BEC regimes and their crossover, with specific results on critical currents linked to experimental observations.

Findings

Critical current behavior varies across the BEC-BCS crossover.

Superfluid properties like vortices and Josephson tunneling are derived.

Results connect theoretical predictions with recent optical lattice experiments.

Abstract

Both the trapping geometry and the interatomic interaction strength of a dilute ultracold fermionic gas can be well controlled experimentally. When the interactions are tuned to strong attraction, Cooper pairing of neutral atoms takes place and a BCS superfluid is created. Alternatively, the presence of Feshbach resonances in the interatomic scattering allows populating a molecular (bound) state. These molecules are more tightly bound than the Cooper pairs and can form a Bose-Einstein condensate (BEC). In this contribution, we describe both the BCS and BEC regimes, and the crossover, from a functional integral point of view. In this description, the properties of the superfluid (such as vortices and Josephson tunneling) can be derived and followed as the system is tuned from BCS the BEC. In particular, we present results for the critical current of the superfluid through an optical lattice and link these results to recent experiments with atomic bosons in optical lattices.