Negative effective refractive index metamaterials at optical frequencies based on superlattices of noble metals and excitonic semiconductors

Super lattices of engineered spherical nanoparticles are considered as model structures exhibiting dielectric and magnetic resonances at optical frequencies. We first show that a lattice of excitonic semiconductor nanoparticles can be used to realize a magnetic medium. Then, either we form a binary superlattice combining the magnetic crystal with an electric one of metal nanospheres, or we coat the nanospheres of the magnetic crystal with a metal layer and consider a single lattice of coated nanospheres. Both these approaches are shown to represent effective routes to realization of three-dimensional (3D) isotropic negative index metamaterials in the visible.