Topological quantum phase transitions of attractive spinless fermions in a honeycomb lattice

TL;DR

This paper explores the phase diagram of a spinless Fermi gas on a honeycomb lattice with attractive interactions, revealing multiple topological and non-topological quantum phase transitions including superfluid and semi-metal phases.

Contribution

It identifies and characterizes multiple topological quantum phase transitions in a honeycomb lattice system with attractive interactions, using mean-field theory.

Findings

Semi-metallic phase at low interactions

Transition to fully gapped superfluid with increasing interaction

Topological transition to gapless superfluid with Dirac dispersion

Abstract

We investigate a spinless Fermi gas trapped in a honeycomb optical lattice with attractive nearest-neighbor interactions. At zero temperature, mean-field theory predicts three quantum phase transitions, two being topological. At low interactions, the system is semi-metallic. Increasing the interaction further, the semi-metal destabilizes into a fully gapped superfluid. At larger interactions, a topological transition occurs and this superfluid phase becomes gapless, with Dirac-like dispersion relations. Finally, increasing again the interaction, a second topological transition occurs and the gapless superfluid is replaced by a different fully gapped superfluid phase. We analyze these different quantum phases as the temperature and the lattice filling are varied.