Optical plasmonic resonances in split-ring resonator structures: an improved LC model

We systematically investigate the resonant behavior of arrays of Ag nano-structures ranging from isolated simple rods, to U-shapes, to single split ring structures. We show that the lowest order plasmonic resonance associated with a rod red shifts as we create a U and SRR into the position normally associated with a simple LC mode. A second mode red shifts and grows in intensity as we extend the arms of the U-shape, and a third mode appears in the spectra as we close the arms and form a split ring structure. We performed simulations of the structures and examine the E-field and current density. The simulations show that the current path is different for these modes. We examine the behavior of the lowest order mode in detail, discuss the effects of skin depth, and present an improved LC model to describe this resonance.