Role of geometry for strong coupling in active terahertz metamaterials

We discuss the influence of geometry and type of meta-atom resonance on important parameters for strong and ultrastrong light-matter coupling experiments based on localized plasmons in planar metamaterials and intersubband plasmons in quantum wells. An analytic model based on the density matrix formalism is used to extract the radiative linewidth, the achievable coupling rate, and its dependence on distance between a single quantum well and a metasurface for five different types of meta-atoms. Depending on these values, the optical response of the coupled system gives rise to different regimes ranging from the weak-coupling regime over the hybridization-induced transparency regime to the strong-coupling regime. As a result of our investigation, we show that the achievable coupling rates exhibit only a weak dependence on the actual geometry and thus the physical nature of the metamaterial resonance. In all cases, the coupling rate can be made large enough to reach the strong-coupling regime by using multiple quantum wells. DOI: 10.1103/PhysRevB.87.075324