Excitation of Localized Plasmons in Metal Nanoshell and Nanotube with Dielectric Cores

Metal nanoshells and nanotubes with dielectric cores are useful structures to change the surface plasmon frequencies in the wide range. Here, our localized plasmon theory derived in the random phase approximation at high frequency condition is applied to investigate the localized plasmon excitations for metal nanoshells and nanotubes with dielectric cores, which are embedded in dielectrics. Assuming that local dielectric functions for metals and dielectrics have step function shapes at the metal and dielectric interfaces in the quasi-static approximation, analytical formulas can be derived for the localized plasmon excitation. It is found that the bonding and antibonding localized surface plasmons are excited when the nanoshell and nanotube have finite thicknesses and that the surface plasmon frequencies can be controlled in the wide range by changing the ratio of the inner radius to the outer one of the nanoshell and nanotube. The localized surface plasmons, however, are not excited in the zero-thickness limit, i.e., two-dimensional shell where only the lights are emitted from the interfaces of dielectric cores and surrounding dielectrics.