Underpinning Hybridization Intuition for Complex Nanoantennas by Magnetoelectric Quadrupolar Polarizability Retrieval

A central idea in plasmonics and metamaterials is to interpret scattering resonances as resulting from hybridization of electric dipoles. Recent developments in metamaterials as well as in plasmonic Fano systems have further included magnetic dipoles and electric quadrupoles in this reasoning. We derive a method to retrieve dipole and quadrupole polarizability tensors of nano scatterers from full-wave simulations, which allows us to underpin this intuitive reasoning by quantifying the existent modes and their strengths in complex nano antennas. By application to a dolmen plasmon structure, we show how the retrieval sheds new light on plasmon induced transparency. Further, we show how to implement radiative corrections to a dipole quadrupole model applicable when scatterers are placed near a surface, sphere, or stratified medium, similar to the known correction of dipole polarizabilities by the local density of optical states. We demonstrate how this model allows us to interpret near field excitation data taken on plasmon antennas deposited on a high-index substrate.