Excitation of Multiple Fano Resonances in Plasmonic Clusters with D2h Point Group Symmetry

Fano resonances in plasmonic nanostructures exhibit sharp resonance and strong light confinement. These properties are very useful for sensing applications, which rely on plasmon line shape engineering. Fano resonances in plasmonic clusters depend on structure symmetry, and this study provides a general understanding of Fano resonances in clusters with D-2h symmetry. We show that, because of the excitation of B-3u and B-2u dark subradiant modes, four kinds of Fano resonances appear in the spectra for hexamers with D-2h symmetry. When a central particle is introduced to form a heptamer, it is shown that, aside from influence on the resonant behaviors or appearance of an additional Fano resonance for a specific polarization, several hybridized dark subradiant modes are excited for both polarizations, and up to eight kinds of Fano resonances appear in the spectra. Plasmonic clusters with D-2h symmetry are suitable for plasmon line shaping, and it is expected that these structures are useful for multiwavelength sensing applications. This study also reveals that cluster symmetry engineering is a favorable method for generating multiple Fano resonances and tuning spectral features. A similar result is obtained for clusters with other symmetries.