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

Using a magneto-optic technique, we have studied field penetration in a sample consisting of several YBCO single crystals merged together on their basal 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 perpendicular to the sample surface and thus results in an almost surface-barrier-free field penetration. The penetration field was measured under conditions of a fully developed and a reduced surface barrier, and the values obtained were compared in these two cases. The results obtained show that the surface barrier causes a substantial delay of field penetration in YBCO single crystals over the whole temperature range. (author)