Microwave absorption studies in new high-Tcsuperconducting oxide systems: Tl-Ba-Ca-Cu-O and Bi-Ca-Sr-Cu-O

Abstract
Microwave absorption studies of the new high-Tc superconducting systems Tl-Ba-Ca-Cu-O (Tc( rho =0)=118 K) and Bi-Ca-Sr-Cu-O (Tc( rho =0)=84 K) were conducted using an X-band EPR spectrometer. The main features observed were (i) a sharp change in the leakage current at Tc; (ii) intense low-field (c; and (iii) a largely field-independent absorption, the intensity of which was found to increase with increasing external magnetic field strength up to 10 kG. The dependence of the intensity on magnetic field is explained in terms of magnetic-field-induced decoupling of grains and field, and temperature-dependent lambda MW/ lambda , where lambda MW is the microwave penetration depth and lambda is the London penetration depth.