Figure 2: The theoretical optical conductivity of graphene.
From: Realization of mid-infrared graphene hyperbolic metamaterials
It is plotted with EF=350 meV and ℏγ=40 meV. These numbers correspond to heavily doped CVD graphene. At the high-frequency end of the spectrum, graphene is lossy because of the interband absorption. At the low-frequency end, graphene is again lossy because of the intraband free-carrier absorption. There is a useful spectral range in between, where the imaginary part of the optical conductivity exceeds the real part. In this particular example, the useful wavelengths range from 2 to 30 μm in the mid-infrared range. The inset shows another example of lightly doped CVD graphene with EF=150 meV and ℏγ=40 meV. The useful wavelength range is smaller when the doping is lower.
