Static disorder-induced renormalization of polariton group velocity

TL;DR

This paper presents a nonperturbative method to quantify how static energetic disorder affects the group velocity of polaritons in microcavities, revealing that disorder can significantly slow polariton propagation, especially with strong exciton energy fluctuations.

Contribution

A new nonperturbative approach that predicts disorder-induced renormalization of polariton group velocity using measurable parameters, without requiring exact diagonalization.

Findings

Disorder slows both lower and upper polaritons.

Slowing is more pronounced when exciton energy fluctuations approach the Rabi splitting.

Results suggest exciton-phonon interactions are key to observed polariton slowdown.

Abstract

Molecular exciton-polaritons exhibit long-range, ultrafast propagation, yet recent experiments have reported far slower propagation than expected. In this work, we implement a nonperturbative approach to quantify how static energetic disorder renormalizes polariton group velocity in strongly coupled microcavities. The method requires no exact diagonalization or master equation propagation, and depends only on measurable parameters: the mean exciton energy and its variance, the microcavity dispersion, and the Rabi splitting. Using parameters corresponding to recently probed organic microcavities, we show that exciton inhomogeneous broadening slows both lower and upper polaritons, particularly when the mean exciton energy fluctuation approaches the collective light-matter coupling strength. A detailed discussion and interpretation of these results is provided using perturbation theory in the limit of weak resonance scattering. Overall, our results support the view that exciton-phonon interactions likely dominate the recent experimental observations of polariton slowdown in disordered media.