The irreversibility line for a melt-textured YBa2Cu30 7_ ~ (YBCO) sample was determined in two orientations of the field H relative to the sample &axis. In both orientations we obtain good fits using a melting equation with quantum correction to describe the Abrikosov lattice melting. The scaling analysis based on a fluctuation theory for 3D systems was applied to our magnetization data allowing the determination to be made of the mean-field critical temperature. Our results are similar to those found in the literature for very clean untwinned samples. We suggest that the Abrikosov lattice melting is weakly affected by quenched disorder, at least in the relatively low fields (H < 50 kOe) and high temperatures (T/T c > 0.8) probed in this work. * Corresponding author.
pinning strength can be found in a collective fluxcreep model [7]. In a more conventional approach the IL is identified with a depinning line, whose solution comes from an equation describing the constant diffusivity, Do(H, T), of the flux lines [8]. Finally, the interpretation of the IL as the melting transition line of the Abrikosov lattice [9-12] has received enough confirmation, and nowadays the melting hypothesis seems to be a well established matter [13][14][15]. The basic idea is that the Abrikosov lattice becomes unstable and melts, when the mean displacement amplitude of the flux lines, (u2) 1/2, reaches an appreciable fraction of the lattice parameter, a 0. This latter condition is usually expressed in terms of the Lindemann criterion, (u2) 1/2= CLaO, with the Lindemann number c L varying between 0.1 and 0.3.
Recently, Blatter et al. [14] discussed the relevance of quantum fluctuations that, combined with thermal fluctuations [11], produce an effective mean