Figure 3.

Iso-frequency contour plot of the GhHC (a) at wavenumber 1600 cm⁻¹ where hBN behaves as a Type-II hyperbolic material (b) at wavenumber 800 cm⁻¹ where hBN acts as a Type-I hyperbolic material; thickness of graphene and hBN in the unit cell, d₁ = 1 nm and d₂ = 100 nm respectively, the chemical potential of graphene, μ_c = 0.5 eV. (c,d) are the zoomed-in view of the specific zone covered by the dashed lines in Fig. 3(a,b), respectively. The shaded regions indicate the bandgap in k-space where no propagating wave is allowed. (e) Iso-frequency contour plot of a graphene-dielectric multilayer hyperbolic metamaterial; thickness of graphene and dielectric in the unit cell, d₁ = 1 nm and d₂ = 100 nm respectively, permittivity of the dielectric ε_d = 2.2, the chemical potential of graphene, μ_c = 1 eV.