Figure 3

(a) The confinement factor and (b) the quality factor for single-layer graphene (red), single- atomic-layer gold (thickness t=0.29 nm, blue), 20-nm gold film (thin gold, cyan) and 10 layers of stacked graphene with an interlayer spacing of 2 nm (multilayer graphene, magenta). (c) The ratio of the magnetic polarizability density of graphene to that of gold, . Red corresponds to the ratio of monolayers of the two materials, while magenta refers to the ratio of stacked graphene to thin gold. The solid regions spanned by graphene correspond to a Fermi energy range of 0.5–1 eV. The loss thresholds associated with optical phonons in graphene at energies >0.2 eV and with interband transitions in gold at energies greater than 2.5 eV are indicated by the vertical dotted lines. The quality factor in (b) is independent of the thickness. Gold is described based on its measured permittivity.²⁵