# Dipolar and Quadrupolar Excitons Coupled to a Nanoparticle-on-a-Mirror Cavity

## TL;DR

This paper analyzes how dipolar and quadrupolar excitons interact with a nanoparticle-on-a-mirror cavity, revealing differences in strong coupling behavior and emission dynamics using analytical and numerical methods.

## Contribution

It introduces a fully analytical two-dimensional transformation optics model to study plasmon-exciton interactions beyond the quasi-static approximation.

## Key findings

- Finite-size effects influence exciton charge distribution.
- Strong coupling phenomena differ between bright and dark excitons.
- Far-field scattering spectra match numerical simulations.

## Abstract

We investigate plasmon-emitter interactions in a nanoparticle-on-a-mirror cavity. We consider two different sorts of emitters, those that sustain dipolar transitions, and those hosting only quadrupolar, dipole-inactive, excitons. By means of a fully analytical two-dimensional transformation optics approach, we calculate the light-matter coupling strengths for the full plasmonic spectrum supported by the nanocavity. We reveal the impact of finite-size effects in the exciton charge distribution and describe the population dynamics in a spontaneous emission configuration. Pushing our model beyond the quasi-static approximation, we extract the plasmonic dipole moments, which enables us to calculate the far-field scattering spectrum of the hybrid plasmon-emitter system. Our findings, tested against fully numerical simulations, reveal the similarities and differences between the strong coupling phenomenology for bright and dark excitons in nanocavities.