J. Phys. I France 6 (1996) 2275-2290
Comparative Description of the Microwave Surface Impedance of Nb, BaKBiO, and YBaCuOA.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, , in Nb, Ba 0.6K 0.4BiO 3, and YBa 2Cu 3O 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 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 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 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 . With due account of the strong-coupling effects, two-band anisotropy, and impurity scattering in YBa 2Cu 3O , the agreement between the generalized BCS model and experimental data is surprisingly good.
© Les Editions de Physique 1996