H-Polarized Terahertz Wave Scattering from On-Substrate Graphene Strip Grating: Electromagnetically Induced Transparency

We analyze numerically the H-polarized plane wave scattering and absorption by an infinite grating of flat graphene strips lying on a dielectric substrate of finite thickness. The full-wave treatment is based on the analytical semi-inversion, performed with the aid of explicit solution of the Riemann-Hilbert Problem. The result of this procedure is a Fredholm second-kind infinite matrix equation for the Floquet harmonic amplitudes. Thus, the corresponding code is meshless and has a guaranteed convergence. Numerical results show that if the strip width and periodicity have microsize dimensions such a metasurface demonstrates complicated frequency-selective behavior. Namely, three natural mode types with different Q-factors are present: substrate modes, plasmon strip modes, and lattice modes. The latter modes do not exist if the substrate is absent and can have ultra-high Q-factors. As graphene’s conductivity depends on its chemical potential, the transparency and reflectivity of such a metasurface can be tuned in wide range. However, the tunability is spoiled at the lattice-mode resonances.