Properties of Hybridized Modes in Core–Shell Scatterers

The character of resonances in plasmonic core–shell structures is analyzed. In particular, the focus is on the behavior of the weaker (antibonding) resonance. Using the residue expansion of the polarizability, it is shown that to maximize the effect of the antibonding resonance, the ratio of the core radius to the whole sphere radius should be 0.596. The polarizability-based results are compared with full Mie scattering calculations showing fair agreement up to size parameters $x=1/3$.