Abstract
We have investigated critical current related properties of high-T-c thin films such as the temperature dependence of the critical current density J(c)(T), the normalized relaxation rate of the current from the critical level S(T), the dependence of the effective energy barrier against vortex motion on the current density U-eff(J) and the temperature dependence of the superfluid density n(s)(T) proportional to lambda(ab)(-2)(T). The measurements of the critical current J(c) have been performed on YBCO and TlBCCO ring-shaped films. The magnitude of J(c) and its relaxation have been obtained from the magnetic self-field of the persistent current circulating in a ring at the critical level. We found that the nanoscopic phase separation in the a-b planes of high-T-c thin films is responsible for the changes in J(c)(T), S(T), U-eff (J) and n(s)(T).