Bose-Einstein Condensation in Gap-Confined Exciton-Polariton States

TL;DR

This paper investigates how confinement mechanisms in GaAs/AlGaAs heterostructures influence exciton-polariton condensation, highlighting the roles of negative effective mass and photonic energy gaps in achieving low-threshold condensation.

Contribution

It provides a combined theoretical and experimental analysis of polariton condensation in BIC and lossy modes, emphasizing the impact of mode lifetime and spatial quantization.

Findings

Low-threshold condensation occurs in effective traps created by laser excitation.

Polariton BIC modes exhibit slightly lower thresholds due to suppressed radiative losses.

Condensation thresholds are influenced by mode lifetime and spatial confinement.

Abstract

The development of patterned multi-quantum well heterostructures in GaAs/AlGaAs waveguides has recently allowed to achieve exciton-polariton condensation in a topologically protected bound state in the continuum (BIC). Remarkably, condensation occurred above a saddle point of the polariton dispersion. A rigorous analysis of the condensation phenomenon in these systems, as well as the role of the BIC, is still missing. In the present Letter we theoretically and experimentally fill this gap, by showing that polariton confinement resulting from the negative effective mass and the photonic energy gap in the dispersion play a key role in enhancing the relaxation towards the condensed state. In fact, our results show that low-threshold polariton condensation is achieved within the effective trap created by the exciting laser spot regardless of whether the resulting confined mode is long-lived (polariton BIC) or short-lived (lossy mode). In both cases, the spatial quantization of the polariton condensate and the threshold differences associated to the corresponding state lifetime are measured and characterized. For a given negative mass, a slightly lower condensation threshold from the polariton BIC mode is found and associated to its suppressed radiative losses as compared to the lossy one.