Superfluid Transitions in Bosonic Atom-Molecule Mixtures near a Feshbach Resonance

We study bosonic atoms near a Feshbach resonance and predict that, in addition to standard normal and atomic superfluid phases, this system generically exhibits a distinct phase of matter: a molecular superfluid, where molecules are superfluid while atoms are not. We explore zero- and finite-temperature properties of the molecular superfluid (a bosonic, strong-coupling analog of a BCS superconductor), and study quantum and classical phase transitions between the normal, molecular superfluid, and atomic superfluid states.

Figure 1

Mean-field phase diagram for a bosonic atom-molecule mixture, showing molecular (MSF) and atomic (ASF) superfluid phases.

Figure 2

Phase diagram for a bosonic atom-molecule mixture in $d=3$, expressed in terms of detuning $\nu$ and temperature $T$. It illustrates a finite-$T$ tricritical point at $T_{c0}$ and a quantum critical point at ${\nu }_c(n,0)$. In the weakly interacting limit appropriate to experiments the ratio $T_{c1}^{\infty }/T_{c2}^{\infty }=2^{5/3}$.

Figure 3

The $2\pi$ atomic condensate vortex in ASF splits into a $\pi +\pi$ vortex pair connected by a “normal” domain wall.