Interface and Bulk Standing Waves Drive the Coupling of Plasmonic Nanostar Antennas

Finite element simulations of the optical behavior of gold nanostars in water reveal a new view of collective electron cloud oscillations, where localized surface plasmon resonances coexist with coherent delocalized interface waves, i.e., propagating surface plasmons. Gold nanostar spikes long enough to allow propagating polaritons and short enough to resonate with the spherical core serve as the substrate for the observed overlap between propagating modes and localized hot spots. Transverse plane plots reveal bulk polaritons coupled to surface ones. In light of these observations, we explore the mechanisms that drive plasmonic coupling in nanostars from the single spike level to multispiked and multiparticle systems.