Universal relationship between critical currents and nanoscopic phase separation in high-T-c thin films

We have investigated critical current related properties of high-T-c thin f ilms 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 supe rfluid 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-sh aped films. The magnitude of J(c) and its relaxation have been obtained fro m the magnetic self-field of the persistent current circulating in a ring a t 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).