Enhanced Excitation Energy Transfer under Strong Light-Matter Coupling: Insights from Multi-Scale Molecular Dynamics Simulations

TL;DR

This study uses multi-scale molecular dynamics simulations to clarify how strong light-matter coupling influences exciton transport, revealing that dark states and cavity lifetime limit polariton propagation, which has implications for designing efficient exciton transport systems.

Contribution

The paper provides a detailed molecular dynamics simulation analysis explaining the diffusive propagation of polaritons and the role of dark states and cavity lifetime in exciton transport.

Findings

Polaritons propagate diffusively due to reversible population transfers.

Dark states transiently trap excitations, extending propagation beyond polariton lifetime.

Cavity lifetime limits the ballistic propagation of polaritons.

Abstract

Exciton transport can be enhanced in the strong coupling regime where excitons hybridise with confined light modes to form polaritons. Because polaritons have group velocity, their propagation should be ballistic and long-ranged. However, experiments indicate that organic polaritons propagate in a diffusive manner and more slowly than their group velocity. Here, we resolve this controversy by means of molecular dynamics simulations of Rhodamine molecules in a Fabry-P\'{e}rot cavity. Our results suggest that polariton propagation is limited by the cavity lifetime and appears diffusive due to reversible population transfers between polaritonic states that propagate ballistically at their group velocity, and dark states that are stationary. Furthermore, because long-lived dark states transiently trap the excitation, propagation is observed on timescales beyond the intrinsic polariton lifetime. These insights not only help to better understand and interpret experimental observations, but also pave the way towards rational design of molecule-cavity systems for coherent exciton transport.