TEM-like optical mode of a coaxial nanowaveguide.

We study propagation of electromagnetic waves in a nanocoaxial waveguide for frequencies around and below the surface plasmon frequency. We show, that for frequencies sufficiently lower than the surface plasmon frequency, the waveguide supports a plasmon polariton mode that resembles, and indeed reduces to the conventional TEM mode of the conventional coaxial transmission line, known in the radiotechnology.