Figure 4.

Repulsive forces with high bandwidth. (a) The spectra of the force acting on a vertical dipole at a height h=0.1λ above an Au/nanoporous polymer (n = 1.05) semi-infinite stack metamaterial with f_Au = 0.02 = 1/50 for different unit cell sizes and for the equivalent homogeneous anisotropic effective medium. The thickness of gold and polymer slabs (in nm) is annotated for each plot. (b) The spectra of 2D sheet conductivity of a single sheet of graphene using the Kubo formula^60,61, modelled with a scattering rate Γ=1.29 meV and chemical potential μ_c=1 eV. Regions of positive imaginary part of conductivity result in negative equivalent permittivity. (c) The spectra of the force acting on a dipole at a height h=0.1λ above a graphene/nanoporous polymer (n = 1.05) semi-infinite stack metamaterial for t_{unit cell} = 15 nm and the effective medium approximation. The forces are calculated using Equation (1).