Anisotropy of the electrical resistance in high-T-c granular superconductors under magnetic field

The electrical resistance of granular high-T-c superconductors submitted to a magnetic field and crossed by a supercritical current strongly depends o n the angle between magnetic field and current density. In monocrystalline samples, this effect may be simply explained in terms of the angle-dependen t coupling between fluxoids and current. In the case of polycrystalline sup erconductors, an alternative explanation is needed to take into account the effect of the granular structure. In this paper, we propose a quantitative model in which the resistance is mainly determined by the resistive transi tion of weak links. The electrical anisotropy is related to the inhomogeneo us distribution of local magnetic field intensities and local current densi ties in the weak links, due to the magnetic screening effect of the superco nducting grains and to the angular distribution of weak links surfaces. The theoretical results of this model are compared to the experimental ones ob tained on a YBCO specimen under different physical conditions.