Cavity plasmonics: large normal mode splitting of electric and magnetic particle plasmons induced by a photonic microcavity.

We couple localized plasmon modes in nanowire pairs with resonator modes of a microcavity. Depending on the position of the nanowire pair in the resonator, the electric (symmetric) or magnetic (antisymmetric) plasmon mode is coupled, manifested by a huge anticrossing in the dispersion diagram. We explain this behavior by taking the symmetry and spatial distribution of the electric fields in the resonator into account. Experimental spectra verify the predicted mode-splitting due to the resonant coupling and agree well with theory. Our work can serve as a model system for far-field plasmon-plasmon coupling and paves the way toward enhanced localized plasmon-plasmon interaction in photonically coupled three-dimensional Bragg structures.