On the importance of grain boundaries in high-Tc films: simulation results

The importance of the distribution and ``weakness'' of grain boundary junctions in the magnetic field dependence of the transport critical current in HTc films is assessed through simulations. The system is studied with the applied field either parallel or perpendicular to the c axis of the sample. For realistic sample parameters, it is demonstrated that the presence of ``high'' misorientation angles between grains depresses the zero - field critical current density in both orientations, and provokes a transition from pinning-mediated to Fraunhoffer-like field dependencies of the critical current density. Our results also suggest that there is a threshold misorientation angle above which the critical current density remains constant.