Strong interactions and bi-excitons in a polariton mixture

TL;DR

This paper develops a many-body theory revealing Feshbach resonances and bi-exciton effects in a polariton mixture, aligning with experimental observations and highlighting complex decay channels.

Contribution

It introduces a minimal theoretical model for bi-exciton Feshbach resonances in polariton BECs, matching experimental data and predicting decay behaviors.

Findings

Identification of a bi-exciton Feshbach resonance in polariton spectra

Extraction of biexciton energy and decay rates from experiments

Prediction of dominant decay channels beyond dissociation

Abstract

We develop a many-body theory for the properties of exciton-polaritons interacting strongly with a Bose-Einstein condensate (BEC) of exciton-polaritons in another spin state. Interactions lead to the presence of a two-body bound state, the bi-exciton, giving rise to a Feshbach resonance in the polariton spectrum when its energy is equal to that of two free polaritons. Using the minimal set of terms to describe this resonance, our theory recovers the main findings of two experiments probing interaction effects for upper and lower polaritons in a BEC. This strongly supports that Feshbach physics has indeed been realized, and we furthermore extract the energy and decay of biexciton from the experimental data. The decay rate is predicted to be much larger than that coming from its dissociation into two free polaritons indicating that other decay channels are important.