Topological transitions of gapless paired states in mixed-geometry lattices

TL;DR

This paper explores how mixed-geometry lattices of different fermionic species can host exotic multiband pairing states, revealing a rich phase diagram with topological transitions and Lifshitz points.

Contribution

It introduces a novel mixed-geometry lattice system and demonstrates the emergence of complex pairing phases and topological transitions not previously characterized.

Findings

Identification of a rich phase diagram with gapped and gapless phases.

Discovery of Fermi surface topology-driven Lifshitz transitions.

Stabilization of gapless phases through interband pairing contributions.

Abstract

We propose a mixed-geometry system of fermionic species selectively confined in lattices of different geometry. We investigate how such asymmetry can lead to exotic multiband fermion pairing in an example system of honeycomb and triangular lattices. A rich phase diagram of interband pairing with gapped and gapless excitations is found at zero temperature. We find that the two-band contribution of the honeycomb lattices to the paired state helps to stabilize the gapless phase with one or two Fermi surfaces. We also show that the Fermi surface topology further divides the gapless phase into subclasses between which the system undergoes density-driven Lifshitz transitions.