Members of the ZOTERAC consortium have recently published a new article in Physical Review Letters on the control of the optical properties of ZnO-based metamaterials by tuning the quantum resonances of the structures. This effect is illustrated using the intersubband transitions in ZnO/(Zn,Mg)O quantum wells.
The article can be accessed here.
(a) Schematic of the toy model structure. A stack along the z direction of two alternating media: layer 1, thickness l1 and a resonant permittivity ε1; layer 2, thickness l2, dispersionless with a permittivity ε2. (b) Optical phase diagram showing the sign inversion conditions for both in-plane and z components of the effective permittivity as a function of the normalized frequency ω/ωp and of the thickness ratio. 3D inset images: isofrequency surfaces plotted in k space for the different behaviors. The resonance energy is ω0 = ωp/2. For simplicity, the curves are plotted imposing ε2 = ε∞ = 1 and γ = 0. (c) Comparison between the refraction effect in (right) a conventional and in (left) a negative index material.
From Hierro et al. "Optical Phase Transition in Semiconductor Quantum Metamaterials", Phys. Rev. Lett. 123, 117401 (2019).