Thickness-dependent effective surface resistances of nearly ferroelectric superconductors

The effective surface resistance of nearly ferroelectric superconducting film in the dielectriclike response is theoretically investigated based on the electrodynamics of the nearly ferroelectric superconductors. We calculate the intrinsic film surface resistance for isolated thin film and the effective surface resistance for a superconductor/dielectric layered structure. It is found that the thickness-dependent surface resistance has two different behaviors separated by a critical film thickness being equal to the London penetration length. That is, a nonresonant dependence is seen when the film thickness is less than the London penetration length, and an anomalously resonant behavior is found when the film thickness is larger than the London penetration length. The nonresonant dependence is similar to that of a cuprate superconductor and it further is characterized by some other critical thicknesses. As for the anomalous resonant region it is seen only in a nearly ferroelectric superconductor.