Negative-index metamaterials from nanoapertures

We introduce an approach towards the design of metamaterials where the dielectric and magnetic activity is caused by resonances in dielectric nanocavities embedded in metal. The simplest implementation of this concept is a rectangular nanoaperture in a thin metallic stripe. We show that the electromagnetic field of the resonance eigenmodes is primarily concentrated in the dielectric medium. Even modes affect the effective permittivity, whereas odd modes evoke dispersion in the effective permeability. The negative permittivity provided by the metallic stripes allows potentially for a negative effective index near the first magnetic resonance. Advantages and disadvantages of this structure compared to metamaterials where the resonant eigenmodes are mainly localized at metallic nanoparticles are discussed.