THE PINNING POTENTIAL NEAR THE IRREVERSIBILITY TEMPERATURE IN HIGH-T-C OXIDE SUPERCONDUCTORS

Temperature and magnetic field dependences of the critical current den sity J(c) and the averaged pinning potential U-p were measured in orde r to understand the mechanism of the irreversibility line in high-T-c oxide superconductors by the use of an ac inductive method. The flux m otion in the pinning potential well in the vicinity of the irreversibi lity temperature T-irr was also investigated. As the temperature incre ases to TirrUp decreases nearly equal to the thermal activation energy k(B)T(irr). This result suggests that the irreversibility line is the thermally induced depinning line.