A phenomenological description for unusual surface impedance behaviors of high-T-c thin film in weak DC magnetic field

A phenomenological description is presented in this paper for unusual surfa ce impedance (Z(s)) behaviour of high-T-c thin film in weak DC magnetic fie ld (B-DC) Unusual Z(s), surface impedance behaviour of YBCO thin film, name ly, Z(s) decreases with B-DC, is observed with microstrip technique at 77 K . In our description, the exponential dependence of the increase of superco nducting electron density on B-DC is assumed to explain unusual Z(s) behavi our. Combined with the two-fluid model (TFM) and the coupled-grain model, t he field dependence of Z(s) is computed. Results based on this model agreed with the experimental results qualitatively. (C) 1999 Elsevier Science B.V . All rights reserved.