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

Abstract

Following a number of investigations into the nature of critical currents in superconducting thin films of YBaCu2O7−δ (YBCO), we provide a theoretical analysis of the possible origins of crossover effects. The framework within which our analysis is based involves local condensates described by the Landau-Ginzburg (LG) model and coupled to their neighbors via Josephson weak links. Within the LG phenomenology critical current behavior depends on the presence and strength of the various expansion coefficients. We show that the corresponding critical exponent for jc varies between 32 and 1. We then incorporate the oxygen deficiency effect, which scales the critical temperature as well as other model parameters. In the last part of the paper we investigate the effect of weak links on the critical current’s exponent and again show that the latter may vary between the LG and Ambegaokar-Baratoff regimes of 32 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)].

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