Crossover between Energy Transparency Resonance and Rabi Splitting in Antenna–Molecule Coupled Systems

We theoretically study crossover characteristics between the energy transparency (ET) and the Rabi splitting (RS) that occur in a coupled system comprising molecules and metallic antennas sustaining localized plasmon polaritons. Numerical demonstrations reveal that, in the crossover regime, it is hard to distinguish ET from RS using only the spectrum of the total system because of similarity of their spectral shapes. However, the absorption processes of molecules are physically different between these two effects, that is, in ET, light with the frequency in resonant with the original molecular level is absorbed by the molecules, whereas in RS, such light is not absorbed by the molecules due to the level splitting. We discuss how the essential difference between these physical mechanisms appears in observed quantities and propose how one can clearly identify them approaching these physical mechanisms.