Anomalous microwave absorption (X-band) in a Y-Ba-Cu-O system

Microwave absorption measurements, carried out in the temperature range 77 K - 105 K on samples of the Y-Ba-Cu-O system prepared by a special heat treatment, emphasize two types of zero-magnetic field signals with opposite phases changing one type to another. The signal associated to the superconducting state (S-signal) appears as following to an initial real microwave (or plus optical) absorption (A-signal) in the sample, what suggests the induced character of the superconducting state. A value of (9.4±0.3) 10-2 eV for the activation energy of the A-S dynamical transition process was estimated. The temperature and microwave power dependences of the S-signal and its presence at a temperature much higher than usual Tc (123 phase), connected to the resistive transition (above 200 K), registered in AC, support the presence in these samples of a superconducting phase (or of structure able to generate, in given conditions, a superconducting state) of a very high critical temperature. (Author)