Quantum metric driven transition between superfluid and incoherent fluid

TL;DR

This paper investigates how quantum metric influences the transition from incoherent exciton fluid to superfluidity in a flat band system, specifically in a Lieb lattice bilayer, revealing a quantum metric-driven phase change.

Contribution

It introduces a model showing that increasing quantum metric induces a transition from incoherent fluid to superfluid in flat band systems, beyond mean field approximation.

Findings

Quantum metric controls exciton fluid coherence.

Transition from incoherent fluid to superfluid driven by quantum metric.

Model of Josephson junction array captures the transition.

Abstract

We study the interplay between repulsive interaction and superfluidity in flat band system. We consider spatially indirect excitons in the Lieb lattice bilayer as an example. We show that due to the presence of repulsive interaction, the excitons may form an incoherent fluid. By increasing the quantum metric, the exciton fluid experiences a transition into the superfluid phase. Such transition may be captured by a model of Josephson junction array, which is beyond mean field description.