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

TL;DR

This paper explores how dipolar interactions in multi-component ultracold fermion systems lead to mixed triplet and singlet pairing, with potential spontaneous time-reversal symmetry breaking.

Contribution

It demonstrates that dipolar anisotropy naturally induces both triplet and singlet pairing, and shows how their mixing can break time-reversal symmetry in ultracold fermion systems.

Findings

Triplet p_z-like polar pairing is dominant with dipolar interactions.

Short-range attraction enhances singlet pairing, making it nearly degenerate with triplet.

Triplet and singlet pairings can mix with a phase of ±π/2, breaking time-reversal symmetry.

Abstract

The symmetry properties of the Cooper pairing problem for multi-component ultra-cold 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.