Plasmon polaritons in slot waveguides: Simple model calculations and a full nonlocal quantum mechanical treatment

We study the propagation of electromagnetic waves in a slot waveguide made of a simple (Al) as well as a complex (Ag) metal for frequencies around and below the surface plasmon frequency. Simple model calculations are compared with the full, nonlocal, quantum mechanical treatment based on Feibelman's d-function formalism. We show that for frequencies sufficiently lower than the surface plasmon frequency, but still in the infrared or visible range, the waveguide supports a plasmon polariton mode that resembles, and indeed reduces to, the conventional TEM mode of the conventional slot transmission line, known in the radiotechnology. This opens up the possibility of employing ideas of the radiotechnology in the visible range.