How to make a negative index of refraction material?
For physical reasons, the frequencies of magnetic resonances in ordinary atomic and molecular systems are much lower than that of electric dipole resonances, which virtually excludes a possibility to find a naturally occurring molecular/crystalline material with simultaneously negative dielectric permittivity and magnetic permeability. Negative refractive index (NIR) must be invented and made artificially. The basic principle of electromagnetic meta-material design is a so-called “super-lattice” or a “photonic crystal”. A super-lattice is a periodic pattern in usual dielectric or metallic material, such as, periodic alternation of two different materials, with period that is much larger than the typical atomic or crystalline size, and typically comparable to or a few times smaller than the wavelength of light. Under such conditions, each of the alternating materials can be described locally with its bulk dielectric tensor, while the whole structure can be globally be described as an ef
