Manipulating transverse magnetic modes in waveguide using thin plasmonic materials

Transverse magnetic modes propagate freely for any frequency in a parallel plated waveguide. Here, it is shown that when two thin plasmonic materials are attached to the metal walls of the waveguide, a bandgap emerges due to the excited surface plasmon polaritons. As the plasmonic materials become thin enough, a critical thickness is observed. For any width larger than such a value, the bandgap is fixed, otherwise a tunable bandgap can be achieved (different widths induce different bandgaps). For application, such a tunable bandgap system can be utilized to design a band-stop filter for terahertz frequencies with a high quality factor.