Phenomenological model of the microwave surface impedance of high-Tc superconducting films

A modified phenomenological model of the microwave surface impedance is proposed. The model is based on the experimental data of measurements of the microwave characteristics of high-temperature superconducting (HTS) films. Numerous experimental results are analysed. The model description of the HTS single crystals and the HTS epitaxial films are compared. It is shown that these two objects are of different physical nature and should be described by different models. The phenomenological model of the HTS film surface impedance based on the modified two-fluid model takes into account specific features of the HTS films. The model of the real and imaginary parts of the surface impedance uses the model parameter gamma, which is responsible for the superconducting and normal charge carrier density. This parameter is used for a description of the temperature dependence of the London penetration depth lambda(L)(T) including lambda(L)(0). The relaxation time model also uses the gamma parameter in combination with the residual resistance parameter alpha. One can conclude that the parameter gamma is the main characteristic of the model and can be considered as a figure of merit of the HTS film microwave properties.