What is the origin of glassy behavior in the high-T(sub c) oxides

The anomalous low-field magnetic properties of the high-T(sub c) oxide crystals have been interpreted alternatively in terms of a superconductive glass state or, more recently, giant flux creep. The glass picture as proposed assumes the occurrence of intragranular Josephson junctions on a length scale small compared to the penetration depth, and has been used to explain the properties of both single-crystal and ceramic samples. The flux creep picture deals only with pinning forces and ignores weak links, and thus far has been applied only to single crystals. We show here that neither of these models adequately describes the behavior of ceramic materials. A physically accurate picture of such materials must take into account intergranular Josephson junctions and resultant grain decoupling at low magnetic fields.