UNUSUAL RESISTIVITY BROADENING IN THE MIXED-STATE OF NDBA2CU3O7-DELTACRYSTALS GROWN BY A CRYSTAL-PULLING TECHNIQUE

In order to clarify the origin of a strong peak effect in the magnetiz ation curve of NdBa2Cu3O7 - delta crystals, we investigated the superc onductivity transition behavior of the in-plane resistivity in static magnetic fields up to 8 T. Comparing the results for the samples exhib iting and not exhibiting the peak effect, we found that the former (pe ak effect sample) shows lower resistivity above the vortex melting tem perature. This implies that the pinning force is effective in the vort ex liquid state. We also found that the normal state resistivity behav iors of some samples were unusual, indicating inhomogeneous current fl ow. These results suggest an existence of sheet-like pinning centers p erpendicular to the conduction planes. (C) 1998 Elsevier Science B.V. All rights reserved.