The resistance of a granular high-T-c superconductor cooled below the transition temperature T-co and submitted to a magnetic held is found to depend on the angle between the external field H and the macroscopic current density j. To explain this effect a simple model is proposed, in which the flux exclusion by the superconducting grains makes the local magnetic field in the intergrain regions strongly inhomogeneous. The probability for a weak link to be submitted to a local field of intensity HI is supposed to be dependent on the angle theta between the normal n to the weak link surface and the external field H. This creates a structural anisotropy in the distribution of weak links undergoing the resistive transition under the effect of magnetic field and current. A theoretical expression is then obtained for the ratio eta of the resistivity rho(perpendicular to) in a direction perpendicular to the applied magnetic field H to the resistivity pit in a direction parallel to H. On the basis of the assumption that the resistive transition of the weak links depends only on the moduli of H-I and j, the resistivity can be described as a tensor of order 2, completely determined by rho(parallel to) and rho(perpendicular to). The theoretical predictions of the model are compared with the results of experimental measurements on a bulk specimen of granular superconductor. [References: 9]
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