The structure of the ground superfluid state in a gas of Fermi atoms near the Feshbach resonance

TL;DR

This paper investigates the ground state structure of a Fermi gas near a Feshbach resonance, revealing a superfluid composed of coherently bound quasi-molecules and atom pairs, with detailed spectral and collective excitation properties.

Contribution

It introduces a variational framework to describe the ground state of Fermi gases near Feshbach resonance, accounting for both open and closed channel pairing.

Findings

Identification of a superfluid state formed by two coherently bound subsystems.

Derivation of equations describing ground state properties at arbitrary parameters.

Prediction of a spectral gap and sound velocity in collective excitations.

Abstract

Within the framework of the variational approach the ground state is studied in a gas of Fermi atoms near the Feshbach resonance at negative scattering length. The structure of the originating superfluid state is formed by two coherently bound subsystems. One subsystem is that of quasi molecules in the closed channel and the other is a system of pairs of atoms in the open channel. The set of equations derived allows us to describe the properties of the ground state at an arbitrary magnitude of the parameters. In particular, it allows one to find a gap in the spectrum of single-particle Fermi excitations and sound velocity characterizing a branch of collective Bose excitations.