Theory for terahertz plasmons of metallic nanowires with sub-skin-depth diameters.

We investigate the propagation properties of terahertz plasmon of a metallic nanowire with sub-skin-depth diameter. By taking the small radius and the huge relative permittivity into account, we establish an approximate analytical description for this kind of surface plasmon. It is shown that the main propagation properties are closely related to the product of the radius of the metallic nanowire and the complex wave number of the metal. In addition, when the radius of the metal wire is smaller than the skin-depth, the size of the modal field is simply proportional to the radius of the metal wire. We also carefully verify these analytical predictions with rigorous numerical simulations.