JOSEPHSON COUPLING, INPLANE PINNING, AND VORTEX DIMENSIONALITY IN BI2SR2CACU2O8+DELTA

The c-axis I-V characteristics of an oxygen overdoped Bi2Sr2CaCu2O8+δ single crystal have been measured to determine the current density Jcc(T) across the CuO2 planes. In zero field, close to Tc, they show large capacitance resistively shunted junction behavior, a signature of phase locking of the Josephson junctions. In the quasi-force-free configuration with an applied field of 2T, the zero-field-cooled Jcc(T) has a nonmonotonic behavior, its decrease at intermediate temperatures coinciding with a change in the form of the I-V curve. History effects are also observed. These features can be explained in terms of both disorder in the in-plane pinning of flux pancakes and a change in the Josephson coupling as the temperature is lowered. © 1995 The American Physical Society.