Field penetration and surface barriers in superconducting Bi2Sr2CaCu2O8+delta whiskers

We have used an array of Hall probes to investigate the spatial dependence of the local magnetic induction of individual superconducting Bi2Sr2CaCu2O8+delta whiskers. At low temperatures (less than or equal to 50 K) the exponential temperature dependence of the field of first flux penetration, H-P(T), is consistent with recent theories of flux penetration by two-dimensional pancake vortices. A power-law dependence at higher temperatures suggests that flux penetrates as three-dimensional lines nearer T-c. We also show directly that at high temperatures the flux distribution is dominated by a surface barrier, whereas at low temperatures bulk pinning appears to dominate.