Enhancement of critical current density under low magnetic fields around 70 K in Bi2Sr2CaCu2Oy superconducting whiskers

Electrical transport measurements for Bi2Sr2CaCu2Oy whiskers with a single-step superconducting transition were carried out at high temperature ranging from 70 to 77 K below the superconducting transition temperature (= 81.5-82.5 K) to investigate critical current density (J(c)) under magnetic fields along the crystal c axis. The J(c) parallel to the crystal a axis, which was estimated from the V-I curves, enhances under several ten oersteds, and then decreases with increasing the magnetic field. This peak effect in the low-field regime at high temperature has temperature dependence in contrast to the case of matching effects.