Advancements in high refractive index media:from quantum coherence in atomic systems to deep subwavelength coupling in metamaterials[Invited]

Refractive index enhancement is crucial in the fields of lithography,imaging,optical communications,solar devices,and many more.We present a review of advancements in the process of designing high refractive index metamaterials,starting from quantum coupling and photonic bandgap materials to metamaterials utilizing deep subwavelength coupling to achieve ever-high values of refractive index.A particular attention is given to experimentally verified schemes in engineering a high index of refraction.The understanding of the evolution of material design from intrinsic electronic states manipulation to meta-atoms design is not only fascinating but also a prerequisite to developing successful devices and applications.