Transport properties of high-temperature grain boundary Josephson junctions

Mechanisms of charge transport across high-critical temperature grain boundary junctions (GBJs) have been analyzed in the framework of an existing phenomenological model. In this model, the microscopic parameters describing the electric transport of GBJs are also used for the description of noise characteristics. Indeed, the same microscopic origin is assumed for both phenomena. Theoretical behaviors have been compared with data available in the literature. The scaling of the characteristic voltages V-c with the critical current density has been successfully accounted for. The dependence of transport parameters on the substrate misorientation angle has been derived. The consistency between experimental data, obtained directly by the current-voltage characteristics, and transport parameters derived by noise measurements confirms that the microscopic origin of electrical transport and noise may be the same. The performed study supports a description of the grain boundary as an array of superconductive channels, separated by non-superconductive regions, these ones allowing the transport of quasiparticle only. The analysis also suggests that the "d-wave" symmetry of the order parameter has relevant effect only on samples characterized by large angles, i.e. in the case of asymmetric 45degrees GBJs. (C) 2001 Elsevier Science B.V. All rights reserved.