Quantum Melting in a Polariton Lattice

TL;DR

This paper investigates a lattice model of dipole-interacting excitons coupled to cavity photons, revealing a rich phase diagram with ordered states and a predicted supersolid phase where polariton condensation coexists with spatial order.

Contribution

It introduces a theoretical model of polariton lattices with exciton interactions, predicting novel phases including a supersolid, based on stability analysis and fluctuation calculations.

Findings

Transition from normal to polariton condensate involves intermediate ordered states.

Prediction of a supersolid phase with coexistence of condensation and spatial order.

Phase diagram includes various stable phases depending on exciton filling.

Abstract

Inspired by the recent experimental observation of strongly coupled polaritons in a Moir\'e heterobilayer, we study a model of dipole-interacting excitons localized on sites of a lattice and coupled to planar cavity photons. We calculate the phase diagram of this system by computing fluctuations around the mean field and determining the stability of the excitation spectrum. We find that the transition from the normal state to a polariton condensate is intermediated by a series of ordered states at partial fillings of the exciton lattice, stabilized by the exciton interactions. In particular we predict a supersolid phase in which a polariton condensate coexists with spatial order.