Topological superfluids on a square optical lattice with non-Abelian gauge fields: Effects of next-nearest-neighbor hopping in the BCS-BEC evolution

TL;DR

This paper explores how next-nearest-neighbor hopping influences topological superfluid phases and quantum phase transitions in a two-component Fermi gas on a square lattice with spin-orbit coupling and Zeeman field, covering the entire BCS-BEC evolution.

Contribution

It classifies superfluid phases by their quasiparticle excitation topology and maps out the resulting quantum phase transitions, highlighting the effects of next-nearest-neighbor hopping.

Findings

Identification of multiple topological superfluid phases.

Observation of reentrant superfluid behavior separated by normal phases.

Changes in Chern number signal quantum phase transitions.

Abstract

We consider a two-component Fermi gas with attractive interactions on a square optical lattice, and study the interplay of Zeeman field, spin-orbit coupling and next-nearest-neighbor hopping on the ground-state phase diagrams in the entire BCS-BEC evolution. In particular, we first classify and distinguish all possible superfluid phases by the momentum-space topology of their zero-energy quasiparticle/quasihole excitations, and then numerically establish a plethora of quantum phase transitions in between. These transitions are further signalled and evidenced by the changes in the corresponding topological invariant of the system, \textit{i.e.}, its Chern number. Lastly, we find that the superfluid phase exhibits a reentrant structure, separated by a fingering normal phase, the origin of which is traced back to the changes in the single-particle density of states.