Figure 5: Extraction of the effective permittivity of the graphene HMM.
From: Realization of mid-infrared graphene hyperbolic metamaterials
(a,b) The ellipsometric angles Ψ and Δ acquired from the graphene-dielectric multilayer structure. The measurement is performed at incident angles of 47°, 57° and 67°. The blue dash lines show the fitting by homogenizing the multilayer structure into a metamaterial with the effective permittivities given by equation 1. We extract from the fitting that EF=365 meV and ℏγ=41 meV. (c) The extracted effective permittivity of the metamaterial, which exhibits an optical topological transition from elliptical to hyperbolic dispersion at 4.5 μm. When the wavelength is at 6 μm, ɛeff,|| equals 2.1+0.9i and ɛeff,⊥ equals 2.1. (d) The extracted optical conductivity of the constituent CVD graphene in the metamaterial.
