Hybridization of Gap Modes and Lattice Modes in a Plasmonic Resonator Array with a Metal-Insulator-Metal Structure

Plasmonic resonator arrays have attracted a great interest as a platform to enhance light-matter interaction and have been examined for their applicability to various types of optical devices, such as sensors, light emitter, and photocatalyst, to name a few. In a plasmonic resonator array, localized and propagating plasmon modes can hybridize, which is known to result in an anticrossing of the plasmon bands in the dispersion curves. However, it was so far unclear how the modal symmetry affects such a hybridization, especially when it occurs at a specific reciprocal lattice point with a high degree of symmetry, for example, the Î" point. In this work, we used momentum-resolved cathodoluminescence-scanning transmission electron microscopy to comprehensively characterize the modal hybridization at the Î" point. Our study reveals theoretically and experimentally the existence of mode symmetry selection rules that specify hybrid pairs of the lattice mode and localized mode.