Transition between flux liquid and flux solid in high-Tcsuperconductors

We have studied flux melting near the ${\mathit{H}}_{\mathit{c}1}$ line in T-Ba-Cu-O using a variational Monte Carlo method. The existence of a flux-liquid phase has been observed and the transition line between flux liquid and flux solid in the H-T phase diagram has been determined. The width of the liquid phase increases with temperature as ${\mathit{T}}^2$ at low temperatures, as predicted by Nelson, and faster than ${\mathit{T}}^2$ at higher temperatures, eventually crossing over to the high-field melting curve.