Intersubband plasmons induced negative refraction at mid-IR frequency in hetero structured semiconductor metamaterials

In this contribution, we report on negative refraction effect occurring in layered semiconductors. The origin of this effect is attributed to the presence of intersubband plasmon resonance induced by the electronic confinement of the electrons in thick quantum wells. Relying on the effective medium theory, we analyse both the in plane and the out of plane effective optical properties of highly doped ZnO/ZnMgO semiconductor material. We theoretically show and experimentally demonstrate that thicknesses and doping levels of each layer can be carefully chosen to feature strong intersubband transitions, leading to type 1 and type 2 hyperbolic response. Understanding the optical properties of intersubband materials in the frame of hyperbolic materials would shed new light on which physical mechanisms are controlling the radiative decay of intersubband plasmon excitations. This approach could be further utilized to designing efficient mid-IR sources.