Superconductivity Research Laboratory, International Superconductivity Technology Center, 1-10-13, Shinonome, Koto-ku, Tokyo 135, Japan
Abstract:
In order to clarify the origin of a strong peak effect in the magnetization curve of NdBa2Cu3O7?δ crystals, we investigated the superconductivity transition behavior of the in-plane resistivity in static magnetic fields up to 8 T. Comparing the results for the samples exhibiting and not exhibiting the peak effect, we found that the former (peak effect sample) shows lower resistivity above the vortex melting temperature. This implies that the pinning force is effective in the vortex liquid state. We also found that the normal state resistivity behaviors of some samples were unusual, indicating inhomogeneous current flow. These results suggest an existence of sheet-like pinning centers perpendicular to the conduction planes.