Condensation of Cavity Polaritons in a Disordered Environment

TL;DR

This paper models cavity polariton condensation in disordered quantum wells, analyzing how weak disorder affects coherence, phase transitions, and spectral properties across different excitation densities.

Contribution

It introduces a mean-field phase diagram for cavity polaritons considering disorder effects and explores the transition from electronic to photon-like condensates.

Findings

Disorder can close the condensate and quench coherence at low densities.

Increasing excitation density restores coherence despite disorder.

Spectral analysis reveals abrupt changes in photon intensity at phase boundaries.

Abstract

A model for direct two band excitons in a disordered quantum well coupled to light in a cavity is investigated. In the limit in which the exciton density is high, we assess the impact of weak `pair-breaking' disorder on the feasibility of condensation of cavity polaritons. The mean-field phase diagram shows a `lower density' region, where the condensate is dominated by electronic excitations and where disorder tends to close the condensate and quench coherence. Increasing the density of excitations in the system, partially due to the screening of Coulomb interaction, the excitations contributing to the condensate become mainly photon-like and coherence is reestablished for any value of disorder. In contrast, in the photon dominated region of the phase diagram, the energy gap of the quasi-particle spectrum still closes when the disorder strength is increased. Above mean-field, thermal, quantum and fluctuations induced by disorder are considered and the spectrum of the collective excitations is evaluated. In particular, it is shown that the angle resolved photon intensity exhibits an abrupt change in its behaviour, going from the condensed to the non-condensed region.