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

The influence of flux pinning on the vortex glass-liquid (GL) phase transit ion and irreversibility in HTSs has been examined on the basis of systemati c 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 t he thermal depinning determined by the minimum value of the macroscopic pin ning strength. The isothermal scaling of the E-J characteristics is directl y related to the nature of the pinning. The irreversibility line can be des cribed as an iso-J line governed by the statistical pin distribution. If we determine the criteria for the irreversibility line, we can describe the i rreversibility line based on the depinning line. The essential physical qua ntity, therefore, can be attributed to the flux depinning.