Ultracold Fermi Gases with Resonant Dipole-Dipole Interaction

The superfluid phases in resonant dipolar Fermi gases are investigated by the standard mean-field theory. In contrast to the crossover from Bose-Einstein condensation (BEC) to Bardeen-Cooper-Schrieffer superfluid in Fermi gases with isotropic interactions, resonant dipolar interaction leads to two completely different BEC phases of the tight-binding Fermi molecules on both sides of the resonance, which are characterized by two order parameters with distinct internal symmetries. We point out that, near the resonances, the two competitive phases can coexist, and an emergent relative phase between the two order parameters spontaneously breaks time-reversal symmetry, which could be observed in momentum resolved rf spectroscopy.

Figure 1

Order parameters (upper row) and chemical potential (lower row) for a two-species dipolar Fermi gas in the resonance regime with $y=-1$ (left column) and 1 (right column). Here, ${\epsilon }_F=k_F^2/(2M)$ is the Fermi energy.

Figure 2

Quasiparticle spectral function, $\ln A(\mathbf{k},\omega )$, at $\cos {\theta }_{\mathbf{k}}=\pm 0.39$ (upper row) and $\pm 0.9$ (lower row) for a superfluid in the multiple-channel resonant regime. From the left to the right columns, $1/(k_F{a}_{02})=-1$, 0, and 1. Other parameters are $y=1$ and $\gamma /{\epsilon }_F=0.2$.

Figure 3

$y$ dependence of the angular distributions for $|w_1({\theta }_{\mathbf{k}})|$ (left panel) and $|w_2({\theta }_{\mathbf{k}})|$ (right panel).