Demonstration of Robust Plexcitonic Coupling in Organic Molecules-Mediated Toroidal Meta-Atoms

Hybridized plexcitonic states are conventionally excited via robust coupling between resonantly coordinated plasmonic modes and molecular excitons. Here, numerical and experimental studies for the strong plexcitonic coupling and Rabi splitting of dynamic toroidal dipole moment in a plasmonic meta-atom are presented. It is shown that introducing semiconductor PbS quantum dot aggregates, as a narrow gap semiconductor, with a bulk bandgap of 0.41 eV and a large exciton Bohr radius (tunable over the entire near-infrared band) to the developed toroidal plasmonic metamaterial allows for the substantially strong plexcitonic coupling with the Rabi splitting of 150 meV in the near-infrared wavelengths. By computing the density of states for photons, the enhancement in the intensity of the photoluminescence spectra is quantitatively and qualitatively demonstrated. The results verified the luminescence enhancement due to the strong near-field coupling in the proposed unit cell, and cavity quantum electrodynamics Purcell effect. It is believed that this understanding paves a new method to study the plexcitonic coupling principle in nontraditional resonances and high-order modes to employ them as novel approaches in the coming generation and modern nanophotonic technologies.