Phase transitions of polariton condensate in 2D Dirac materials

TL;DR

This paper explores how the interplay of Coulomb interaction, electron-photon coupling, and Berry phase effects in 2D Dirac materials leads to complex phase transitions in polariton condensates, including topological phases.

Contribution

It introduces a detailed phase diagram for polariton condensates in 2D Dirac materials considering topological and symmetry-breaking transitions.

Findings

Identification of topological phase transitions in polariton condensates.

Discovery of quantum anomalous Hall and quantum spin Hall phases.

Rich phase diagram due to competition between e-ph coupling and Coulomb interactions.

Abstract

For the quantum well in an optical microcavity, the interplay of the Coulomb interaction and the electron-photon (e-ph) coupling can lead to the hybridizations of the exciton and the cavity photon known as polaritons, which can form the Bose-Einstein condensate above a threshold density. Additional physics due to the nontrivial Berry phase comes into play when the quantum well consists of the gapped two-dimensional (2D) Dirac material such as the transition metal dichalcogenide (TMDC) MoS$_2$ or WSe$_2$. Specifically, in forming the polariton, the e-ph coupling from the optical selection rule due to the Berry phase can compete against the Coulomb electron-electron (e-e) interaction. We find that this competition gives rise to a rich phase diagram for the polariton condensate involving both topological and symmetry breaking phase transitions, with the former giving rise to the quantum anomalous Hall and the quantum spin Hall phases.