Metamaterials: What are they? What are they good for?

Our inventory of useful materials contains many natural and man made composites, such as celluose, steel, cement, etc. with unique properties resulting from macroscopic, or mesoscopic heterogeneity. In most cases, their utility can be attributed to the role of the reduced dimensionality (compared to that of their macroscopic constituents) of the heterogeneity relative to an excitation coherence length. The coherence lengths can be single particle quantum wavelengths (photon, spin, etc.) or ensemble classical statistical lengths (skin and absorption depths, diffusion length, etc.). The size of heterogeneity in most composites can be described by a distribution function, characteristic of the dominant processing rates, but inevitably broadened by thermal and other fluctuations. Recently, techniques, such as multilayer deposition, lithography, self assembly, etc. have been used to fabricate metamaterials; unique composites with artificially narrowed distributions of heterogeneity. This narrowing can be exploited to generate a wide variety of interesting new materials, such as artificial magnetodielectrics, exchange spring magnets, ferroelectric and semiconductor superlattices, photonic crystals, etc. Heterogeneity is always introduced in these composites to localize excitations. Localization can either, selectively create (or annihilate) states that did not (or did) exist in the constituent materials. This talk will discuss how the response functions of a great variety of new material composites are interpreted within the metamaterials schema. A new metamaterials synthesis strategy is also presented, in which artificially narrowed heterogeneity is introduced into materials to realize new responses precluded by physics constraints from occurring in the constituent materials.