Phases and phase transitions of Bose condensed light: phase separation effect

TL;DR

This paper explores the phase diagram of Bose-Einstein condensed light in 2D, revealing a unique photon-pair condensate caused by disorder and a phase separation phenomenon leading to non-uniform condensate distribution.

Contribution

It introduces a novel geometrical pairing mechanism and demonstrates phase separation effects in photon condensates due to orientational disorder.

Findings

Discovery of a photon-pair condensate induced by disorder

Identification of phase separation leading to non-uniform condensate distribution

Construction of the phase diagram at the mean field level

Abstract

Recent realization of Bose-Einstein condensation of light in 2D provides a new platform for studying novel phases and phase transitions. The combination of low effective mass of the confined light and the presence of the dye molecules with randomly oriented directions of the dipolar transition engages a competition between disorder and the tendency to forming algebraic off-diagonal order. The phase diagram of possible phases is constructed at the mean field level. One of the phases is the condensate of photon pairs induced solely by the orientational disorder. Such a {\it geometrical } mechanism of pairing has no analogy in other systems. It is also found that the photon condensantion can proceed as a phase separation effect leading to a non-uniform distribution of the condensate and dye molecules.