Vortex-line shape and second peak effect in high-Tc superconductors

The origin of the second peak effect in melt-textured YBa2Cu3O7-δ was investigated using the sweeping rate dependence of magnetic hysteresis loops. An anomalous change of the vortex-line shape was found around the second peak position. This phenomenon was ascribed to the competition between elastic energy Eel and pinning energy Epin of the flux system. By comparing it with the results of crystal samples such as YBCO, NCCO and Pb-doped BSCCO, we concluded that this characteristic is uniform for these high-Tc superconductors and should be responsible for the widely observed second peak effect in magnetization measurements.