BCS-BEC crossover in a system of microcavity polaritons

TL;DR

This paper explores the transition of microcavity polaritons from a Bose-Einstein condensate to a BCS-like state across different densities, providing a detailed phase diagram and analyzing experimental relevance.

Contribution

It introduces a comprehensive phase diagram for polariton condensates including fluctuation effects, revealing a crossover from bosonic to BCS-like behavior at accessible densities.

Findings

Condensation temperature T_c behaves like point bosons at low densities.

T_c approaches BCS-like mean-field results at higher densities.

Current experiments operate in the density regime where BCS-like behavior dominates.

Abstract

We investigate the thermodynamics and signatures of a polariton condensate over a range of densities, using a model of microcavity polaritons with internal structure. We determine a phase diagram for this system including fluctuation corrections to the mean-field theory. At low densities the condensation temperature, T_c, behaves like that for point bosons. At higher densities, when T_c approaches the Rabi splitting, T_c deviates from the form for point bosons, and instead approaches the result of a BCS-like mean-field theory. This crossover occurs at densities much less than the Mott density. We show that current experiments are in a density range where the phase boundary is described by the BCS-like mean-field boundary. We investigate the influence of inhomogeneous broadening and detuning of excitons on the phase diagram.