Interaction-Range Effects and Universality in the BCS-BEC Crossover of Spin-Orbit Coupled Fermi Gases

Abstract

We explore the evolution of a ultracold quantum gas of interacting fermions crossing from a Bardeen-Cooper-Schrieffer (BCS) superfluidity to a Bose-Einstein condensation (BEC) of molecular bosons in the presence of a tunable-range interaction among the fermions and of an artificial magnetic field, which can be used to simulate a pseudo-spin-orbit coupling (SOC) and to produce topological states. We find that the crossover is affected by a competition between the finite range of the interaction and the SOC and that the threshold ${\lambda }_B$ for the topological transition is affected by the interactions only in the small pair size, BEC-like, regime. Below ${\lambda }_B$, we find persistence of universal behavior in the critical temperature, chemical potential, and condensate fraction, provided that the pair correlation length is used as a driving parameter. Above threshold, universality is lost in the regime of large pair sizes. Here, the limiting ground state departs from a weakly-interacting BCS-like, so that a different description is required. Our results can be relevant in view of current experiments with cold atoms in optical cavities, where tunable-range effective atomic interactions can be engineered.

References in corpus (5)

• Observation of Bose-Einstein Condensation of Molecules
• Degenerate Quantum Gases with Spin-Orbit Coupling
• A Bose-Einstein Condensate in a Uniform Light-induced Vector Potential
• BCS-BEC crossover induced by a synthetic non-Abelian gauge field
• Signatures of pairing and spin-orbit coupling in correlation functions of Fermi gases