Figure 4.

Propagation constants ${\beta }_{+}$ (solid red lines) and ${\beta }_{-}$ (dashed blue lines) for SPP modes in the double-layer graphene sheets versus the interlayer distance d (a) with and (b) without taking into account the interband conductivity of graphene calculated by using the analytical solutions of Equation (12). Parameters correspond to a weak coupling regime for wavelength $2.56\mathsf{\mu }\mathrm{m}$ in Table 1.