On the nature of the bonding and antibonding metallic film and nanoshell plasmons

Metallic films and nanoshells exhibit bonding and antibonding plasmon resonances formed by hybridization of plasmon resonances associated with the two surfaces confining the metal. For both structures the lower energy bonding plasmon resonance is characterized by a symmetric alignment of the charge densities. In this Letter we present a physically intuitive explanation for why the repulsive symmetric charge alignment results in a low energy bonding plasmon. We also show that the plasmon dispersion for a planar thin film can be obtained from the plasmon resonances of a metallic nanoshell in the limit of infinite radius.