Discussion of temperature-dependent epsilon-near-zero effect in graphene

In the present paper, we discuss the temperature-dependent epsilon-near-zero (ENZ) effect in graphene arising in the framework of its isotropic model. The effect was theoretically investigated in detail using a simplified model design of the slot line containing a graphene layer in which all other effects are eliminated allowing us to focus solely on the ENZ effect. With the reduction of graphene effective temperature, the ENZ effect in the near-IR wavelength range was found to become pronounced even for structures and metasurfaces for which it has been considered neglectable and has not been previously observed at room temperatures. This temperature-dependent behaviour was interpreted analytically within the approximation in which the real part of the graphene dielectric constant is considered vanishingly small in comparison with the imaginary part (this condition is always satisfied at the ENZ point in graphene). Furthermore, the results presented in the paper may be potentially helpful in the construction of an experiment designed to finally prove or disregard the applicability of the isotropic model of graphene.