A BCS wavefunction approach to the BEC-BCS crossover of exciton-polariton condensates

TL;DR

This paper investigates the transition between BEC and BCS regimes in exciton-polariton condensates using an extended wavefunction approach that includes cavity photon effects, revealing distinct low and high density behaviors.

Contribution

It introduces a BCS wavefunction framework for exciton-polariton condensates that captures both Bose-Einstein and photon-dominated regimes, including intermediate BCS-like states.

Findings

Identifies a BCS-like regime with non-zero momentum pairing.

Predicts experimental signatures in photoluminescence.

Describes a crossover from exciton BEC to photon-dominated regimes.

Abstract

The crossover between low and high density regimes of exciton-polariton condensates is examined using a BCS wavefunction approach. Our approach is an extension of the BEC-BCS crossover theory for excitons, but includes a cavity photon field. The approach can describe both the low density limit, where the system can be described as a Bose-Einstein condensate (BEC) of exciton-polaritons, and the high density limit, where the system enters a photon dominated regime. In contrast to the exciton BEC-BCS crossover where the system approaches an electron-hole plasma, the polariton high density limit has strongly correlated electron-hole pairs. At intermediate densities, there is a regime with BCS-like properties, with a peak at non-zero momentum of the singlet pair function. We calculate the expected photoluminescence and give several experimental signatures of the crossover.