Intensity of the microwave absorption in high-temperature superconductors

Abstract

Absorption of microwaves vs. magnetic field near zero field by high-temperature superconductors shows a large number of equally spaced lines in the superconducting state. The intensity of these lines vs. magnetic field is similar to that of Josephson currents which are induced in such oxide superconductors. There is a strong temperature dependence of the intensity with a peak somewhat below the superconducting transition temperature, T_c. The lines and microwave absorption completely vanish above T_c. The intensity of these low-field lines has been examined in four different samples, YBa₂Cu₃O₇, YBa₂Cu₃O₇–Ag, BiSrCaCu₂O_y and Bi_1.6Pb_0.4Sr₄Ca₂Cu₃O_y. In each case the intensity as a function of temperature shows a shallow minimum well below T_c. The temperature, T₀, at which this shallow occurs was determined. A discussion of the liquid-like behaviour related to the flux liquid is given. Motional narrowing of the lines was detected.