J. Phys. I France
Volume 6, Numéro 12, December 1996
Page(s) 2275 - 2290
DOI: 10.1051/jp1:1996217
J. Phys. I France 6 (1996) 2275-2290

Comparative Description of the Microwave Surface Impedance of Nb, BaKBiO, and YBaCuO

A.A. Golubov1, M.R. Trunin1, A.A. Zhukov1, O.V. Dolgov2 and S.V. Shulga3

1  Institute of Solid State Physics, 142432 Chernogolovka, Moscow district, Russia
2  P.N. Lebedev Physical Institute, Moscow, Russia
3  Institute of Spectroscopy, Troitsk, Russia

(Received 23 April 1996, accepted 3 June 1996)

Measurements of microwave impedance versus temperature, $Z_{\rm s}(T)$, in Nb, Ba 0.6K 0.4BiO 3, and YBa 2Cu 3O $_{7-\delta}$ are given. The measurements were made by the "hot finger" cavity perturbation technique. The electromagnetic properties of Nb are in a good quantitative agreement with the isotropic s-wave BCS theory. This model can also describe the experimental $Z_{\rm s}(T)$ curves in Ba 0.6K 0.4BiO 3 crystals if the nonhomogeneous broadening of the superconducting transition is properly taken into account. The behavior of the microwave impedance of YBa 2Cu 3O $_{7-\delta}$ disagrees with the isotropic BCS theory. This suggests a strong anisotropy of the order parameter in this compound. Since the controversy between s- and d-wave descriptions of YBa 2Cu 3O $_{7-\delta}$ properties has not been resolved yet, we have checked a simpler strongly anisotropic s-wave model. Calculations by this model have been compared to measurements on YBa 2Cu 3O $_{7-\delta}$. With due account of the strong-coupling effects, two-band anisotropy, and impurity scattering in YBa 2Cu 3O $_{7-\delta}$, the agreement between the generalized BCS model and experimental data is surprisingly good.

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