Ensembles of plasmonic nanospheres at optical frequencies and a problem of negative index behavior

Arrays of metallic nanoparticles support individual and collective plasmonic excitations that contribute to unusual phenomena like surface enhanced Raman scattering, anomalous transparency, negative index, and subwavelength resolution in various metamaterials. We have examined the electromagnetic response of dual Kron's lattice and films containing up to three monolayers of metallic nanospheres. It appears that open cubic Kron's lattice exhibits `soft' electromagnetic response but no negative index behavior. The close-packed arrays behave similarly: there are plasmon resonances and very high transmission at certain wavelengths that are much larger than the separation between the particles, and a `soft' magnetic response, with small but positive effective index of refraction. It would be interesting to check those predictions experimentally.