Exceptional compound plasmon–polariton waves guided by a metal film embedded in a uniaxial dielectric material

The canonical boundary-value problem for the propagation of compound plasmon–polariton (CPP) waves, guided by a symmetric structure comprising a metal film embedded in a uniaxial dielectric material, was formulated and solved. In addition to unexceptional CPP waves whose field strength, in the dielectric material, decays exponentially with distance from the nearest dielectric/metal interface, this structure can also guide exceptional CPP waves whose fields, in the dielectric material, decay as the product of a linear function and an exponential function of distance from the nearest dielectric/metal interface. An explicit solution for exceptional CPP-wave propagation was derived and spatial field profiles for exceptional CPP waves were computed. At most, two exceptional CPP waves were found to propagate in two different directions within each quadrant of the interfacial plane.