Metamaterials and Transformation Optics
Metamaterials may be classified into two categories: LSPR-based and non-LSPR metamaterials. LSPR-based metamaterials such as negative index metamaterials rely upon LSPR phenomenon and hence the best performing plasmonic materials are noble metals followed by metal nitrides, further followed by TCOs (Tassin et al., 2012). Non-LSPR metamaterials rely upon effective medium behavior of composite materials and examples are cloaks, hyperbolic metamaterials, and epsilon-near-zero (ENZ) materials. As a general note, most of the metamaterial implementations of transformation optics fall into the category of non-LSPR metamaterials. Such metamaterials benefit a lot from alternative plasmonic materials because of their smaller Im{εm}.