Fluctuation conductivity and critical currents in YBCO films

A comparative analysis of the results obtained in measurements of the fluctuation conductivity and of the critical current density j(c)(T) in YBa2Cu3O7-y films containing various numbers of defects is carried out for the first time. It is found that the value and temperature dependence of the fluctuation conductivity are interrelated with the values and temperature dependences of the critical current and resistivity of the samples. It follows from measurements of the fluctuation conductivity that the variation of these temperature dependences is directly related to the variation of the number of defects and, hence, the number of pinning centers in the films studied. It is shown that in films containing practically no defects the j(c)(T) curve completely follows a model giving j(c)(T) in high-T-c superconductors with low-angle grain boundaries between crystallization blocks. On the other hand, if the sample has a specific defect structure that is formed under certain conditions in c-oriented epitaxial high-T-c superconducting films, one observes a sharp increase in j(c) and in the slope of the j(c)(T) curve. (C) 2003 American Institute of Physics.