Hybrid Metastructures in the Epsilon-Near-Zero Regime

Abstract

The objects of study of this chapter are hybrid structures whose resonant behavior can be understood in terms of an exotic propagation regime called epsilon-near-zero (ENZ). We embark in the engaging challenge of investigating an apparently counterintuitive light propagation regime in which light assumes a phase velocity faster than the speed of light compensated by an approximately zero group velocity. The occurrence of such a fascinating feature is illustrated in simple, daily-use materials like silver as well as in sophisticated hybrid multilayers. These latter systems embed graphene as a flat and active technological core and have been found to be the ideal platform to design ultrafast and attojoule electro-optical modulation systems. In the end, we point the spotlight over a novel hybrid architecture called hyperbolic metamaterial. In particular, we study a deeply subwavelength (a few nanometers thick) hybrid structure involving graphene as a metal, and we show how, under the appropriate conditions of extreme anisotropy, this flat lens breaks the diffraction limit with incomparable optical resolution of λ/1660.