SURFACE-SENSITIVE PARAMAGNETIC MEISSNER EFFECT IN YBA2CU3OX SINGLE-CRYSTALS

It is demonstrated that the paramagnetic Meissner effect observed in s ome of our YBa2Cu3Ox single crystals is associated with an anomalous s urface layer. This surface layer, which has a superconducting transiti on temperature slightly higher than the bulk, develops when the crysta ls are annealed below 400 degrees C. When the layer is mechanically re moved, the paramagnetic Meissner effect disappears and the crystals be have as normal. Our results demonstrate that the Meissner effect can b e masked by unusual properties of a thin surface layer. Thus the measu red field-cooled magnetization may not represent the bulk Meissner eff ect.