Odd-parity topological superfluidity for fermions in a bond-centered square optical lattice

TL;DR

This paper proposes a method to realize two-dimensional topological odd-parity superfluidity in a square optical lattice, leveraging symmetry and interband pairing, leading to topological phases with s-wave interactions.

Contribution

It introduces a scheme for creating topological odd-parity superfluids in optical lattices using interband pairing and symmetry protection, a novel approach in the field.

Findings

Topological superfluid phases can be achieved with s-wave interactions.

Fermi surfaces of different parity can be tuned to match.

Topological features are inferred from symmetry and confirmed numerically.

Abstract

We propose a physical scheme for the realization of two-dimensional topological odd-parity superfluidity in a spin-independent bond-centered square optical lattice based upon interband fermion pairing. The D4 point-group symmetry of the lattice protects a quadratic band crossing, which allows one to prepare a Fermi surface of spin-up fermions with odd parity close to the degeneracy point. In the presence of spin-down fermions with even parity populating a different energetically well separated band, odd-parity pairing is favored. Strikingly, as a necessary prerequisite for pairing both Fermi surfaces can be tuned to match well. As a result, topological superfluid phases emerge in the presence of merely s-wave interaction. Due to the Z2 symmetry of these odd-parity superfluids, we infer their topological features simply from the symmetry and the Fermi-surface topology as confirmed numerically.