Fig. 1: Existence condition of TE graphene plasmons in the negative and positive refractive-index environments.
From: Confined transverse-electric graphene plasmons in negative refractive-index systems
a Structural schematic. The monolayer graphene is located in a symmetric environment with the relative permittivity εr1 = εr2 = εr and the relative permeability μr1 = μr2 = μr. b Existence condition of TE graphene plasmons in environments with various values of εr and μr. c Surface conductivity of monolayer graphene as a function of frequency at 300 K. The emergence of TE graphene plasmons in environments with μr > 0 requires Im(σs) < 0, which exists in the frequency range of ħω/μc > 1.667. In contrast, their emergence in environments with μr < 0 requires Im(σs) > 0, existing in the range of ħω/μc < 1.667. Here we set the chemical potential μc = 0.2 eV and the relaxation time τ = 0.2 ps. G0 = e2/4ħ is the universal optical conductivity.
