Uncovering Temperature-Dependent Exciton-Polariton Relaxation Mechanisms in Perovskites

TL;DR

This study investigates how temperature influences exciton-polariton relaxation in perovskites, revealing mechanisms like biexciton-assisted pathways and cavity detuning effects that enable efficient relaxation even at cryogenic temperatures.

Contribution

It uncovers the primary relaxation mechanisms in perovskite polaritons and demonstrates how cavity tuning and intrinsic scattering can optimize polariton relaxation pathways.

Findings

Thermal activation causes a bottleneck regime in polariton relaxation.

Intrinsic scattering mechanisms can overcome the bottleneck effect.

Efficient relaxation to zero in-plane momentum achieved at cryogenic temperatures.

Abstract

State-of-the-art hybrid perovskites have demonstrated excellent functionality in photovoltaics and light-emitting applications, and have emerged as a promising candidate for exciton-polariton (polariton) optoelectronics. In the strong coupling regime, polariton formation and Bose-Einstein condensation (BEC) have been demonstrated at room-temperature in several perovskite formulations. Thermodynamically, low-threshold BEC requires efficient scattering to $k_{||}$ = 0, and many applications demand precise control of polariton interactions. Thus far, the primary mechanisms by which polaritons relax in perovskites remains unclear. In this work, we perform temperature-dependent measurements of polaritons in low-dimensional hybrid perovskites with high light-matter coupling strengths ($\hbar \Omega_{Rabi}$ = 260$\pm$5 meV). By embedding the perovskite active layer in a wedged cavity, we are able to tune the Hopfield coefficients and decouple the primary polariton relaxation mechanisms in this material for the first time. We observe the thermal activation of a bottleneck regime, and reveal that this effect can be overcome by harnessing intrinsic scattering mechanisms arising from the interplay between the different excitonic species, such as biexciton-assisted polariton relaxation pathways, and isoenergetic intracavity pumping. We demonstrate the dependence of the bottleneck suppression on cavity detuning, and are able to achieve efficient relaxation to $k_{||}$ = 0 even at cryogenic temperatures. This new understanding contributes to the design of ultra-low-threshold BEC and condensate control by engineering polariton dispersions resonant with efficient relaxation pathways, leveraging intrinsic material scattering mechanisms for next-generation polariton optoelectronics.