Mixed triplet and singlet pairing in ultracold multicomponent fermion systems with dipolar interactions

The symmetry properties of the Cooper pairing problem for multicomponent ultracold dipolar molecular systems are investigated. The dipolar anisotropy provides a natural and robust mechanism for both triplet and singlet Cooper pairing to first order in the interaction strength. With a purely dipolar interaction, the triplet $p_z$-like polar pairing is the most dominant. A short-range attractive interaction can enhance the singlet pairing to be nearly degenerate with the triplet pairing. We point out that these two pairing channels can mix by developing a relative phase of $\pm \frac{\pi }{2}$, thus spontaneously breaking time-reversal symmetry. We also suggest the possibility of such mixing of triplet and singlet pairing in other systems.

Figure 1

(Color online) The eigenvalues $w_{tri}^z$ for the spin triplet ${\varphi }^z$ channel and $w_{si}^{s+d}$ for the singlet ${\varphi }^{s+d}$ channel. The latter depends on the short-range $s$-wave interaction $V_{00;0}$.