Application of a phenomenological model for the surface impedance in high temperature superconducting films

Abstract

We report the application of a phenomenological model for the microwave surface impedance in high temperature superconducting films. This model is based on the modified two-fluid model, in which the real and imaginary parts of the surface impedance use the modelling parameter γ. This is responsible for the superconducting and normal charge carrier density and is used for the description of the temperature dependence of the London penetration depth λ L (T) including λ L (0). The relaxation time model also uses the γ parameter in combination with the residual resistance parameter α. The parameter δ 1 << 1 provides a finite value of the relaxation time at T = 0. The normal conductivity is described by the metals conduction model and the phenomenological description of the normal conductivity contains four parameters: δ 1 , γ, α, and δ 2 . The parameter δ 2 << 1 is responsible for the non-pairing part of the charge carrier at T = 0. Temperature dependence of σ n (T) is a result of the competition between the increase of the relaxation time and the decrease of the normal charge-carrier density. We applied this model to analyze experimental results of MgB 2 , YBa 2 Cu 3 O 7-δ and GdBa 2 Cu 3 O 7-δ superconducting material.