Thermalization of fluorescent protein exciton-polaritons at room temperature

TL;DR

This paper demonstrates that fluorescent protein exciton-polaritons can be thermally equilibrated at room temperature, enabling potential applications in polaritonic devices and circuits.

Contribution

It introduces a new fluorescent protein molecule, mScarlet, for efficient thermalization of exciton-polaritons at ambient conditions and provides experimental evidence of equilibrium and metastable states.

Findings

Effective polariton cooling at room temperature.

Observation of thermalization close to lattice temperature.

Switching from equilibrium to metastable states at threshold.

Abstract

Fluorescent proteins (FPs) have recently emerged as a serious contender for realizing ultralow threshold room temperature exciton-polariton condensation and lasing. Our contribution investigates the thermalization of FP microcavity exciton-polaritons upon optical pumping under ambient conditions. We realize polariton cooling using a new FP molecule, called mScarlet, coupled strongly to the optical modes in a Fabry Perot cavity. Interestingly, at the threshold excitation energy (fluence) of ~ 9 nJ/pulse (15.6 mJ/cm2), we observe an effective temperature, Teff ~ 350 +/- 35 K close to the lattice temperature indicative of strongly thermalized exciton-polaritons at equilibrium. This efficient thermalization results from the interplay of radiative pumping facilitated by the energetics of the lower polariton branch and the cavity Q factor. Direct evidence for dramatic switching from an equilibrium state into a metastable state is observed for the organic cavity polariton device at room temperature via deviation from the Maxwell-Boltzmann statistics at k = 0 above the threshold. Thermalized polariton gases in organic systems at equilibrium hold substantial promise for designing room temperature polaritonic circuits, switches, and lattices for analog simulation.