Far-infrared graphene plasmonic crystals for plasmonic band engineering.

We introduce far-infrared graphene plasmonic crystals. Periodic structural perturbation-in a proof-of-concept form of hexagonal lattice of apertures-of a continuous graphene medium alters delocalized plasmonic dynamics, creating plasmonic bands in a manner akin to photonic crystals. Fourier transform infrared spectroscopy demonstrates band formation, where far-infrared irradiation excites a unique set of plasmonic bands selected by phase matching and symmetry-based selection rules. This band engineering may lead to a new class of graphene plasmonic devices.