Figure 9: Dyakonov plasmonics: schematic showing (a) isofrequency curve of conventional plasmons on an isotropic gold film. The circular isofrequency curve corresponds to the fact that plasmons can propagate in all directions (blue arrows). (b) Isofrequency curve becomes hyperbolic when an anisotropic slab is placed on top of the gold film. This occurs in the range of frequencies when conventional plasmons which occur along the high-symmetry directions are allowed in one direction (blue arrow) but are not allowed in the perpendicular direction (red arrow).