A theoretical study of terahertz surface plasmons on a cylindrical metal wire

This study addresses some theoretical issues of interest to surface plasmon propagation along a metal-wire waveguide at terahertz (THz) frequencies. The conductor is characterized by a shallow field penetration depth at microwave frequencies and the transparency to frequencies above the ultraviolet. Falling between these two regimes, THz surface plasmons are thus particularly sensitive to the electron dynamics in the metal wire. Also, with evanescent fields both inside and outside, surface plasmons are known to be loosely bound to the metal wire, which further complicates the behavior of surface plasmons. These issues are examined here in a comparative study under AC- and DC-conductivity models. Depending on the wire radius, the frequency dependence of the conductivity has either a very significant effect on the Ohmic loss or no effect at all, while an opposite trend is found for the wave attenuation rate. Extensive data on the wave attenuation constant is also presented and interpreted. The results show details of its frequency scaling as well as a sensitive dependence on the wire radius. The low-loss advantage is clear for a large radius (millimeters and above), while degrading rapidly toward sub-skin-depth radius. Published by AIP Publishing.