Unconventional superfluidity in quasi-one-dimensional systems

We show that an unconventional superfluid triggered by spin-orbit coupling is realized for repulsively interacting quasi-one-dimensional fermions. A competition between spin-singlet and -triplet pairings occurs due to the breaking of inversion symmetry. We show that both superfluid correlations decay algebraically with the same exponent except for special coupling constants for which a dominant superfluid is controlled by the spin-orbit coupling. We also discuss a possible experiment to observe such phases with cold atoms.

Figure 1

A two-coupled-fermionic-ladder system with SOC along the rung direction. Due to the SOC, the rung hopping term takes a complex value and depends on the spin.

Figure 2

Phase diagram as a function of the SOC parameter $\Phi$ for a repulsive Hubbard interaction $U$. The parentheses denote subdominant fluctuations. The subdominant fluctuations disappear at $\Phi =0,\pm \pi /2,\pi$ (dotted line), and both the pairing types are equally balanced at $\Phi =\pm \pi /4,\pm 3\pi /4$.