Critical current in YBa2Cu3O7 ceramics

Measurements of critical currents using a four-point direct current (dc) and an alternating magnetic field method have been performed on several superconducting YBa2Cu3O7 ceramics at 77 K. In the presence of a constant magnetic field, the critical currents obtained with the alternating field method are several orders of magnitude larger than the critical currents measured by the dc method. Also, the authors observed a minimum in the dc critical current as a function of applied transverse magnetic field. Several authors have suggested that these ceramics behave as individual superconducting grains coupled by Josephson junctions. In this paper, they explain the two observations above suing that model