Magnetic field penetration in YBa2Cu3O7-delta single crystals under conditions of a reduced surface barrier

Using a magneto-optic technique, we have studied field penetration in a sam ple consisting of several YBCO single crystals merged together on their bas al plane. The bending of field stream lines around crystal edges in such a geometry creates an orientation of the local applied field that is nearly p erpendicular to the sample surface and thus results in an almost surface-ba rrier-free field penetration. The penetration field was measured under cond itions of a fully developed and a reduced surface barrier, and the values o btained were compared in these two cases. The results obtained show that th e surface barrier causes a substantial delay of field penetration in YBCO s ingle crystals over the whole temperature range.