FIELD PENETRATION AND SURFACE BARRIERS IN SUPERCONDUCTING BI2SR2CACU2O8+DELTA WHISKERS

We have used an array of Hall probes to investigate the spatial depend ence of the local magnetic induction of individual superconducting Bi2 Sr2CaCu2O8+delta whiskers. At low temperatures (less than or equal to 50 K) the exponential temperature dependence of the field of first flu x penetration, H-P(T), is consistent with recent theories of flux pene tration by two-dimensional pancake vortices. A power-law dependence at higher temperatures suggests that flux penetrates as three-dimensiona l lines nearer T-c. We also show directly that at high temperatures th e flux distribution is dominated by a surface barrier, whereas at low temperatures bulk pinning appears to dominate.