Synthetic Plasmonic Nanocircuits and the Evolution of Their Correlated Spatial Arrangement and Resonance Spectrum

Optical nanocircuits, inspired by electrical nanocircuits, provide a versatile platform for tailoring and manipulating optical fields at the subwavelength scale, which is vital for developing various innovative optical nanodevices and integrated nanosystems. Plasmonic nanoparticles can be employed as promising building blocks for optical nanocircuits with unprecedentedly high integration capacity. Among various plasmonic systems, aggregated metallic nanoparticle, known as oligomers, possess great potential in constructing functional metatronic circuits. Here, the optical nanocircuits comprising special plasmonic oligomers, such as trimers with D_3h symmetry, quadrumers with D_2h symmetry, and their variants with reduced symmetry, are systematically investigated in the metatronic paradigm, both theoretically and experimentally. Our proposed circuit models, based on the displacement current in the oligomers, not only reproduce the resonance spectral details, but also retrieve many hidden physical quantities associated with their optical responses. Guided by the metatronic circuits, the spectral engineering of the oligomers with reduced geometric symmetry is predicted, and subgroup decomposition of several plasmonic quadrumers is examined. Our investigation has revealed a close correlation between the metatronic circuitry and strongly coupled plasmonic oligomers. The observed correlation of spatial arrangement and frequency response in oligomers provides a metatronic guide to modulate plasmonic responses via geometric variation.