Optical magnetism and negative refraction in plasmonic metamaterials

In this review we describe the challenges and opportunities for creating magnetically active metamaterials in the optical part of the spectrum. The emphasis is on the sub-wavelength periodic metamaterials whose unit cell is much smaller than the optical wavelength. The conceptual differences between microwave and optical metamaterials are demonstrated. We also describe several theoretical techniques used for calculating the effective parameters of plasmonic metamaterials: the effective dielectric permittivity eff(!) and magnetic permeability µeff(!). Several examples of negative permittivity and negative permeability plasmonic metamaterials are used to illustrate the theory.