High current carrying networks of Josephson junctions in YBCO films

High-quality YBCO films present a characteristic plateau in the logarithmic plot of the critical currents versus field. This plateau can be attributed in the high-current regime to networks of defects having different sizes and distributions. In addition to the intrinsic defects, we created columnar defects across YBCO films by irradiating sets of samples with 0.25 GeV Au ions at different doses. In this paper we show that the width of the plateau is related to the distribution of defects along the grain boundaries. This distribution can be changed by means of ion irradiation. The experimental results are compared with theoretical models both in the low- and in the high-temperature regime. In the low-temperature regime, a model based on Josephson junction arrays fits optimally the experimental J(c)(B) data. On the contrary, in the high-temperature regime the film behaves almost as a continuum, where the columnar defects emerge as the only effective pins. In this case we refer to a Bose-glass picture.