Transport relaxation phenomena in superconducting Y_(1)Ba_(2)Cu_(3)O_(7-δ)

摘要

Transport relaxation measurements (V-t) were carried out in bulk superconducting Y_(1)Ba_(2)Cu_(2)O_(7-δ) ceramic samples as a function of driving current (I), temperature (T), and external magnetic field (H). The evolution of the V-t curve strongly depends on I, T, and H. The V-t characteristics exhibit several features revealing the details of the evolution of the penetrated state associated with different flow patterns. Analysis of the V-t data showed that the relaxation process originates mainly from the intergranular region. The results provide direct evidence for the relaxation of vortices which are of Josephson-type. From the magnetic field dependence of the V-t curves, we found that there is a transition evolving from the Josephson vortices to the Abrikosov ones. We showed that both the driving current and external magnetic field have determining effects on the shape of the V-t curve and anneal the dynamical states by serving as an effective temperature.