Comment on “Study of the multicritical point in the vortex phase diagram(H∥c)of a weakly pinned crystal ofYBa2Cu3O7−δ”

Abstract

The continuity between the thermally driven first-order vortex lattice melting observed at high temperatures and the disorder-driven transition appearing in the low-temperature region of the vortex phase diagram of ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ (YBCO) is still controversial. Pal et al. have reported a rich vortex phase diagram for relatively clean YBCO crystals, in which, in qualitative agreement with a recent theoretical proposal, the end point of the vortex lattice melting is located well above the disorder-driven transition line. However, the results presented by Pal et al. suggest the existence of domains of different quenched disorder degree in the investigated crystal, and in these conditions the global magnetic measurements cannot lead to definite conclusions about the vortex phase diagram of high-temperature superconductors.