Near-field Analysis of Strong Coupling between Localized Surface Plasmons and Excitons

TL;DR

This paper uses simulations to analyze near-field strong coupling between molecular excitons and localized surface plasmons in aluminum nanodisks, revealing collective effects and energy exchange dynamics.

Contribution

It introduces a simple model for near-field strong coupling analysis, demonstrating collective oscillations and energy exchange phenomena in plasmon-exciton systems.

Findings

Spectral Rabi splitting is smaller in near-field than far-field.

Energy exchange shows out-of-phase beats in the near-field.

Strong coupling exhibits collective oscillations proportional to molecule number.

Abstract

We simulate the near-field effects of strong coupling between molecular excitons and localized surface plasmons, supported by aluminum nanodisks. The simulations are done using a simple model of a two-level system, implemented in a commercial electromagnetic finite-difference time-domain solver. While the Rabi splitting is present in the near-field, its spectral gap is seen to be smaller than the one obtained in the far-field, although it follows a clear square root dependence on the molecular density as expected. Moreover, the energy exchange between the plasmonic mode and the excitonic material is evident in 'beats' within the electromagnetic near-field, which are out of phase with respect to the exciton population. Our results explicitly demonstrate the collective nature of strong coupling, which is expressed by the synchronized population oscillations at the collective Rabi frequency set by the number of molecules interacting with the plasmonic mode. This analysis sheds light on strong coupling effects in the near-field region using a versatile model, which provides a powerful tool to study strong coupling, near-field effects, and light-matter interactions in general.