Highly excited exciton-polariton condensates

TL;DR

This paper investigates high-density exciton-polariton condensates, demonstrating that strong coupling persists at high densities through direct observation of the negative branch, distinguishing it from standard lasing.

Contribution

It provides experimental evidence that exciton-polariton systems remain in strong coupling at high densities, contrary to previous assumptions of transition to lasing.

Findings

Negative branch observed in photoluminescence at high density

Strong coupling regime persists at high excitation densities

Contrasts with previous results indicating lasing transition

Abstract

Exciton-polaritons are a coherent electron-hole-photon (e-h-p) system where condensation has been observed in semiconductor microcavities. In contrast to equilibrium Bose-Einstein condensation (BEC) for long lifetime systems, polariton condensates have a dynamical nonequilibrium feature owing to the similar physical structure that they have to semiconductor lasers. One of the distinguishing features of a condensate to a laser is the presence of strong coupling between the matter and photon fields. Irrespective of its equilibrium or nonequilibrium nature, exciton-polariton have been observed to maintain strong coupling. We show that by investigating high density regime of exciton-polariton condensates, the negative branch directly observed in photoluminescence. This is evidence that the present e-h-p system is still in the strong coupling regime, contrary to past results where the system reduced to standard lasing at high density.