Unified theoretical framework for realizing diverse regimes of strong coupling between plasmons and electronic transitions

Strong coupling between light and quantum mechanical transitions historically observed in atomic optics is now being realized in the solid state using plasmon resonances. Recent experiments on hybrid plasmonic/excitonic systems have reported varied observations such as excitonic splitting, asymmetric line shapes, and dips in scattering spectra. Here, we unite these seemingly disparate empirical observations under a single theoretical framework, illustrating that the same generalized hybrid system allows access to diverse forms of coupling between plasmons and molecular transitions. Simply by modifying the damping rate of the plasmon resonance, it is possible to transition from one regime of coupling to another (e.g., from Rabi splitting to Fano interference). Common experimental handles such as size, shape, and nature of the metal can be varied to tune the regime of coupling, as shown by electrodynamic simulations. We also show that strong coupling can be achieved using simple nanostructure configurations such as a plasmonic core/excitonic shell geometry without the necessity of sophisticated design of near-field hotspots. The unified model developed here will allow rational predictive design of hybrid plasmonic systems for achieving unique control of light on the nanoscale.