Plasma waves in anisotropic superconducting films below and above the plasma frequency

We consider wave propagation inside an anisotropic superconducting film sandwiched between two semi-infinite nonconducting bounding dieletric media such that along the c axis, perpendicular to the surfaces, there is a plasma frequency {omega}{sub p} below the superconducting gap. Propagation is assumed to be parallel to the surfaces in the dielectric media, where amplitudes decay exponentially. Below {omega}{sub p}, the amplitude also evanesces inside the film, and we retrieve the experimentally measured lower dispersion relation branch, {omega}{proportional_to}{radical}({beta}), and the recently proposed higher frequency branch, {omega}{proportional_to}1/{radical}({beta}). Above {omega}{sub p}, propagation is of the guided wave type, i.e.; a dispersive plane wave confined inside the film that reflects into the dielectric interfaces, and the modes are approximately described by {omega}{approx}{omega}{sub p}{radical}(1+({beta}/{beta}{sub 0}){sup 2}), where {beta}{sub 0} is discussed here. {copyright} {ital 1997} {ital The American Physical Society}