Thermalization and Cooling of Plasmon-Exciton Polaritons: Towards Quantum Condensation

TL;DR

This study demonstrates thermalization and cooling of plasmon-exciton polaritons in a nanorod array, indicating progress towards quantum condensation at room temperature through optical pumping and strong coupling effects.

Contribution

It provides experimental evidence of thermalization and cooling of PEPs in a plasmonic array, a key step towards quantum condensation in such systems.

Findings

Thermalization and cooling of PEPs observed with increased optical pumping.

Saturation of strong coupling leads to emission in a weakly coupled band.

Signatures of thermalization are present in both strongly and weakly coupled regimes.

Abstract

We present indications of thermalization and cooling of quasi-particles, a precursor for quantum condensation, in a plasmonic nanoparticle array. We investigate a periodic array of metallic nanorods covered by a polymer layer doped with an organic dye at room temperature. Surface lattice resonances of the array---hybridized plasmonic/photonic modes---couple strongly to excitons in the dye, and bosonic quasi-particles which we call plasmon-exciton-polaritons (PEPs) are formed. By increasing the PEP density through optical pumping, we observe thermalization and cooling of the strongly coupled PEP band in the light emission dispersion diagram. For increased pumping, we observe saturation of the strong coupling and emission in a new weakly coupled band, which again shows signatures of thermalization and cooling.