Crossover effects for critical currents within Landau-Ginzburg phenomenology incorporating Josephson weak links in superconducting thin films of YBaCu2O7-delta

Following a number of investigations into the nature of critical currents i n superconducting thin films of YBaCu2O7-delta (YBCO), we provide a theoret ical analysis of the possible origins of crossover effects. The framework w ithin which our analysis is based involves local condensates described by t he Landau-Ginzburg (LG) model and coupled to their neighbors via Josephson weak links. Within the LG phenomenology critical current behavior depends o n the presence and strength of the various expansion coefficients. We show that the corresponding critical exponent for j(c) varies between 3/2 and 1. We then incorporate the oxygen deficiency effect, which scales the critica l temperature as well as other model parameters. In the last part of the pa per we investigate the effect of weak links on the critical current's expon ent and again show that the latter may vary between the LG and Ambegaokar-B aratoff regimes of 3/2 and 1, respectively. Combining this analysis with an appropriate choice of model parameters we obtain excellent agreement with the recent experimental data of Darhmaoui and Jung [Phys. Rev. B 53, 14 621 (1996)]. [S0163-1829(99)00838-3].