Ms. James et al., FIELD PENETRATION AND SURFACE BARRIERS IN SUPERCONDUCTING BI2SR2CACU2O8+DELTA WHISKERS, Physical review. B, Condensed matter, 56(10), 1997, pp. 5771-5773
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.