Semiclassical Plexcitonics: Simple Approach for Designing Plexcitonic Nanostructures

We present a classical description of the interaction between localized surface plasmon resonances and excitons which can occur in molecular or solid state systems. Our approach consists of adopting a semianalytical description of the surface plasmon resonances in metal nanoparticles and a semiclassical description of the electronic transitions related to the excitonic material. We consider three plasmon-exciton coupling configurations, namely a (or a set of) metal nanoparticle(s) uniformly coated with an excitonic material, a set of metal nanoparticles placed in the vicinity of a sub-wavelength-sized “patch” containing the active material, and the limiting case of a single point dipole coupled to a metal nanoparticle. Our key result is the derivation of the conditions required to achieve strong plasmon–exciton coupling as evidenced by polaritonic splitting. We apply our results to describe recent experimental studies on these hybrid systems. Our study provides a simple, yet rigorous prescription to both analyze and design systems that exhibit strong light–matter interactions as mediated by localized surface plasmon resonances (i.e., particle plasmons).