The Bottom-Up Approach toward Artificial Optical Magnetism in Metastructures

The generation of artificial optical magnetism (AOM) in engineered composites has been the major concept that led to the emergence of the field of metamaterials at the turn of the millennium. Indeed, the proven possibility to manipulate the magnetic permeability of materials at microwave frequencies induced a considerable excitement in the scientific community, as it opened the way to the design of unprecedented tools and devices for the control of light propagation. Extensions to higher frequencies of IR and visible light were soon proposed and tested by downsizing the artificial structures. The fabrication of negative index materials, optical cloaks, and hyperlenses seemed within reach. Two decades later, and after considerable research efforts, the applications of AOM are still scarce and the concept seems to face a number of fundamental physical limits. We review in this chapter the state of the art of the bottom-up approach whereby nanochemistry and colloidal physics are used to engineer hybrid metastructures exhibiting AOM in visible light or near IR.