The Non-universal behaviour of Cold Fermi Condensates with Narrow Feshbach Resonances

TL;DR

This paper develops an effective field theory for cold Fermi atom condensates near narrow Feshbach resonances, revealing non-universal behavior in the equation of state at the unitary limit due to finite-range effects.

Contribution

It introduces a hydrodynamic effective field theory capturing the BEC-BCS crossover for narrow Feshbach resonances, highlighting non-universal effects at unitarity.

Findings

Non-universal behavior of the equation of state at unitarity.

Dependence of the equation of state on the range of inter-atomic forces.

Finite molecular field scale affects the BEC-BCS crossover.

Abstract

In this paper we construct an effective field theory for a condensate of cold Fermi atoms whose scattering is controlled by a narrow Feshbach resonance. We show how, from first principles, it permits a hydrodynamic description of the BEC-BCS crossover from which the equation of state, intimately related to the speed of sound, can be derived. Specifically, we stress the non-universal behaviour of the equation of state at the unitary limit of infinite scattering length that arises when either, or both, of the range of the inter-atomic force and the scale of the molecular field become large.