Strong Coupling of Two-Dimensional Excitons and Plasmonic Photonic Crystals: Microscopic Theory Reveals Triplet Spectra

TL;DR

This paper develops a microscopic Maxwell-Bloch theory to describe strong exciton-plasmon coupling in TMDC-plasmonic crystal hybrids, revealing spectral splitting and multiple emission peaks in plexciton systems.

Contribution

It introduces a self-consistent theoretical framework for TMDC-PC hybrids, enabling explicit calculation of scattered light and guiding experimental exploration of strong coupling phenomena.

Findings

Spectral splitting of over 100 meV in gold-MoSe2 structures.

Identification of three emission peaks in the strong coupling regime.

Hybridization of exciton and plasmon into two plexcitonic bands.

Abstract

Monolayers of transition metal dichalcogenides (TMDC) are direct-gap semiconductors with strong light-matter interactions featuring tightly bound excitons, while plasmonic crystals (PCs), consisting of metal nanoparticles that act as meta-atoms, exhibit collective plasmon modes and allow one to tailor electric fields on the nanoscale. Recent experiments show that TMDC-PC hybrids can reach the strong-coupling limit between excitons and plasmons forming new quasiparticles, so-called plexcitons. To describe this coupling theoretically, we develop a self-consistent Maxwell-Bloch theory for TMDC-PC hybrid structures, which allows us to compute the scattered light in the near- and far-field explicitly and provide guidance for experimental studies. Our calculations reveal a spectral splitting signature of strong coupling of more than $100\,$meV in gold-MoSe$_2$ structures with $30\,$nm nanoparticles, manifesting in a hybridization of exciton and plasmon into two effective plexcitonic bands. In addition to the hybridized states, we find a remaining excitonic mode with significantly smaller coupling to the plasmonic near-field, emitting directly into the far-field. Thus, hybrid spectra in the strong coupling regime can contain three emission peaks.