AN INVESTIGATION OF THE IRREVERSIBILITY LINE IN BI2SR2CACU2O8 SINGLE-CRYSTALS

Measurements of the irreversibility line for a BSCCO single crystal have been made using resistivity, AC susceptibility (ACS), and DC magnetisation. The ACS results were calibrated by measuring a square of silver with similar dimensions. The results are in agreement with previous work which interpreted the AC susceptibility in terms of a skin-depth effect rather than a phase transition. However,discrepancies appear at high fields and a number of explanations are postulated. The behaviour of the resistivity can be divided into two regimes. The low-resistance regime is explained well by the thermally activated flux flow (TAFF) model. At high resistivities the pinning centres are ineffective and flux-flow resistivity should be dominant. However, the Bardeen-Stephen model does not work, but an alternative explanation based on fluctuations fits well.