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Figure 2: Broadband all-angle negative refraction of hyperbolic polaritons. (a) Imaginary part of surface conductivity of graphene metasurface, created by nanostructured graphene as shown in the left region of Figure 1(a) and having an effective anisotropic surface conductivity of . The graphene metasurface supports hyperbolic plasmon polaritons when , i.e., the region highlighted by yellow. The chemical potential of graphene is eV. (b) Bandwidth of graphene metasurface having , as a function of the chemical potential. The phenomenon of all-angle negative refraction of hyperbolic polaritons can happen within this bandwidth. The constant is the universal optical surface conductivity.