We demonstrate the coupling of bright and dark surface lattice resonances (SLRs), which are collective Fano resonances in 2D plasmonic crystals. As a result of this coupling, a frequency stop gap in the dispersion relation of SLRs is observed. The different field symmetries of the low- and high-frequency SLR bands lead to pronounced differences in their coupling to free-space radiation. Standing waves of very narrow spectral width compared to localized surface-plasmon resonances are formed at the high-frequency band edge, while subradiant damping onsets at the low-frequency band edge, leading the resonance into darkness. We introduce a coupled-oscillator analog to the plasmonic crystal, which serves to elucidate the physics of the coupled plasmonic resonances and which is used to estimate very high quality factors for SLRs.

Phys. Rev. X

Rodriguez, S., Abass, A., Maes, B., Janssen, O. T. A., Vecchi, G., & Gómez Rivas, J. (2011). Coupling bright and dark plasmonic lattice resonances. Phys. Rev. X, 1(2, Article number: 21019), 1–7. doi:10.1103/PhysRevX.1.021019