Short-coherence-length superconductors

The new high-T
c
oxides present some anomalous electromagnetic properties, such as low critical current densities, a reversible behavior of the magnetization at fields much lower than H
c2
, and internal Josephson effects, that distinguish them from the conventional low-T
c
metals and alloys. These anomalous properties were first observed in bulk-sintered samples and were often ascribed to the poor connectivity of these ceramics. More recently, a qualitatively similar behavior has been observed in single crystals and oriented films. The fundamental role of the short coherence length in determining the behavior of the high-T
c
oxides is discussed. We show that the short coherence lengths at the local depressions of the order parameter at crystallographic defects lead to reduced critical currents and cause glassy behavior in the vicinity of T
c
.