Contribution of the electric quadrupole resonance in optical metamaterials

Optical metamaterials can exhibit negative index of refraction when both the effective permittivity and permeability are negative. The negative permeability is usually considered to be associated with a magnetic dipole resonance and the contribution from electric quadrupoles is neglected. Here, we show by simulation that the electric quadrupole contribution is actually comparable to that from magnetic dipoles. We propose an experimental scheme to determine the relative contributions from the electric dipole, magnetic dipole, and electric quadrupole of a metallic nanostructure. This can be important in the design of metamaterials.