Fast vortex motion and filamentary phase separation in YBCO and TlBCCO thin films

摘要

We found a correlation between the temperature dependence of the normalized magnetic relaxation rate S(T) = d In J/d In t, and the filamentary phase separation in the a-b planes of high T-c thin films, i.e., the ratio of the amount of an underdoped phase to that of an optimally doped one. These phases are characterized by different temperature dependences of the critical current density J(c)(T). J(c)(T) of the underdoped component is that of the Ginzburg-Landau (CL) one [with J(c)(T) proportional to (T-c - T)(3/2)]. For the phase closer to the optimum doping, J(c)(T) is described by the Ambegaokar-Baratoff (AB) behaviour at low temperatures with a crossover to the GL one above 0.8T(c), which is indicative of the presence of the Josephson nanostructures in the a-b planes. The results revealed that when the amount of the underdoped GL-like phase increases above a certain threshold value, a peak appears in S(T) at a temperature of 20-30 K and its height gradually increases with the magnitude of the critical current flowing through this phase. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 15]