GEOMETRICAL AND DISTRIBUTED SURFACE BARRIERS IN BI2SR2CACU2O8

The local ac magnetic response in Bi2Sr2CaCu2O8 crystals of platelet a nd prism shapes has been measured using microscopic arrays of Hall sen sors. At elevated temperatures the ac response in platelet samples is governed by the geometrical barrier whereas a distributed Bean-Livings ton surface barrier is dominant for the prism-shaped sample. In the lo cal measurements these two barriers display qualitatively different be havior and can be individually studied. Models for the local ac respon se are derived for the two cases and good agreement with experiment is obtained. (C) 1997 Elsevier Science B.V.