Relationship among flux depinning, irreversibility and phase transition in a disordered HTS material

The influence of flux pinning on the vortex glass-liquid (GL) phase transition and irreversibility in HTSs has been examined on the basis of systematic measurements of electric field ( E ) versus current density ( J ) curves in a YBCO thin film. It has been shown that the GL transition is identical to the thermal depinning determined by the minimum value of the macroscopic pinning strength. The isothermal scaling of the E - J characteristics is directly related to the nature of the pinning. The irreversibility line can be described as an iso- J line governed by the statistical pin distribution. If we determine the criteria for the irreversibility line, we can describe the irreversibility line based on the depinning line. The essential physical quantity, therefore, can be attributed to the flux depinning.