Long-wavelength optical properties of a plasmonic crystal composed of end-to-end nanorod dimers

We theoretically investigate the long-wavelength optical properties of a plasmonic crystal composed of end-to-end gold nanorod dimers. The strong coupling between incident light and the electron oscillations inside the nanorods gives rise to a plasmon polariton, which can be analogous to the phonon polariton in an ionic crystal. Huang-Kun-like equations are employed to explore the underlying physical mechanism for both symmetrical and asymmetrical geometries. In the long wavelength limit, the macroscopic dielectric response of the proposed structure is deduced analytically. The polariton dispersion curve shows a typical anticrossing profile in the strong coupling regime and adjacent branches are separated by a Rabi splitting. The resultant polaritonic stop band is validated by the numerical simulations.