Toward Broadband Plasmonics: Tuning Dispersion in Rhombic Plasmonic Crystals

urface plasmon polaritons (SPPs) are collective charge oscillations coupled to light that propagate along a metal-dielectric interface. One strategy to achieve efficient SPP excitation is to pattern the metal surface; then, the momentum mis-match between SPPs and free-space light can be bridged by Bragg vectors inherent in the periodic nanostructures.1,2 The in-tense, localized electromagnetic (EM) fields associated with SPPs can be used to ma-nipulate and enhance light-matter interac-tions at subwavelength scales.3 Hence, peri-odic metallic nanostructures (so-called plasmonic crystals in two dimensions (2D)4