Not Found in Nature: Metamaterials and Metasurfaces
Human-made, optical metamaterials have been touted for more than a decade for their ability to manipulate light in extraordinary ways. In theory, satellite imaging and interstellar telescopes could be dramatically smaller with metamaterial lenses one hundred times thinner than conventional ones. The core concept of metamaterials is to craft materials by using artificially designed and fabricated structural units to achieve the desired properties and functionalities. These structural units—the constituent artificial ‘atoms’ and ‘molecules’ of the metamaterial—can be tailored in shape and size, the lattice constant and interatomic interaction can be artificially tuned, and ‘defects’ can be designed and placed at desired locations. By engineering the arrangement of these nanoscale unit cells into a desired architecture or geometry, one can tune the refractive index of the metamaterial to positive, near-zero, or negative values. Thus, metamaterials can be endowed with properties and functionalities unattainable in natural materials.