When polarons meet polaritons: Exciton-vibration interactions in organic molecules strongly coupled to confined light fields

TL;DR

This paper develops a semi-analytical theory for organic molecules strongly coupled to a cavity, revealing how exciton-vibration and exciton-cavity interactions produce a hybrid ground state called the lower polaron polariton, with implications for vibrational dressing and decoupling.

Contribution

It introduces a temperature-dependent variational approach to simultaneously treat exciton-vibration and exciton-cavity couplings, elucidating the formation of the lower polaron polariton.

Findings

Strong cavity coupling enhances vibrational dressing of the cavity mode.

Vibrational decoupling of dark excitons occurs at strong coupling.

The lower polaron polariton resembles a dressed bare lower polariton in the strong regime.

Abstract

We present a microscopic semi-analytical theory for the description of organic molecules interacting strongly with a cavity mode. Exciton-vibration coupling within the molecule and exciton-cavity interaction are treated on an equal footing by employing a temperature-dependent variational approach. The interplay between strong exciton-vibration coupling and strong exciton-cavity coupling gives rise to a hybrid ground state, which we refer to as the lower polaron polariton. Explicit expressions for the ground-state wave function, the zero-temperature quasiparticle weight of the lower polaron polariton, the photoluminescence line strength, and the mean number of vibrational quanta are obtained in terms of the optimal variational parameters. The dependence of these quantities upon the exciton-cavity coupling strength reveals that strong cavity coupling leads to an enhanced vibrational dressing of the cavity mode, and at the same time a vibrational decoupling of the dark excitons, which in turn results in a lower polaron polariton resembling a single-mode dressed bare lower polariton in the strong-coupling regime. Thermal effects on several observables are briefly discussed.