Exotic pairing symmetry of interacting Dirac fermions on a $\pi$ flux lattice

TL;DR

This study investigates the pairing symmetry of interacting Dirac fermions on a $\pi$-flux lattice, revealing an exotic $ds^*$-wave phase with a fully gapped spectrum, distinct from conventional pairing symmetries.

Contribution

It uncovers a novel $ds^*$-wave pairing symmetry in Dirac fermions on a $\pi$-flux lattice, combining numerical and mean-field analyses to demonstrate its properties.

Findings

The $ds^*$-wave phase is the dominant pairing at strong interactions.

The $ds^*$-wave state is fully gapped, unlike individual $s^*$- and d-wave states.

Degeneracy of $s^*$- and d-wave symmetries is lifted under the Landau gauge.

Abstract

The pairing symmetry of interacting Dirac fermions on the $\pi$-flux lattice is studied with the determinant quantum Monte Carlo and numerical linked cluster expansion methods. The extended $s^*$- (i.e. extended $s$-) and d-wave pairing symmetries, which are distinct in the conventional square lattice, are degenerate under the Landau gauge. We demonstrate that the dominant pairing channel at strong interactions is an exotic $ds^*$-wave phase consisting of alternating stripes of $s^*$- and d-wave phases. A complementary mean-field analysis shows that while the $s^*$- and d-wave symmetries individually have nodes in the energy spectrum, the $ds^*$ channel is fully gapped. The results represent a new realization of pairing in Dirac systems, connected to the problem of chiral d-wave pairing on the honeycomb lattice, which might be more readily accessed by cold-atom experiments.