Backward-propagating slow light in Mie resonance-based metamaterials

We show theoretically that electromagnetic radiation within Mie-based metamaterials can have a negative refractive index and, at the same time, propagate with a group velocity that is of the order of 105 slower than the vacuum one. In the infrared regime, such behaviour is achieved for metamaterials made from binary superlattices of polaritonic and plasmonic microspheres, whilst in the optical regime it is demonstrated for metal-coated semiconductor nanospheres. The results presented are based on rigorous calculations of the frequency band structure of the above metamaterials obtained by the layer multiple-scattering method.