2-DIMENSIONAL DENSITY-FUNCTIONAL APPROACH TO THE ABRIKOSOV VORTEX LATTICE MELTING

We present a theoretical study of the melting of the Abrikosov vortex lattice in the mixed state of high-T-c superconductors. We start from the Ginzburg-Landau theory which provides, in a wide region of the mix ed state, the surface density of the vortex lattice in terms of the ex ternal magnetic field and the temperature. The interaction between vor tex lines is modeled by means of a painwise potential built up as a su m of a hard-core contribution plus a repulsive long-range tail. The fo e energy of the vortex system is evaluated by means of a density-funct ional theory which carries out a nonlocal treatment of the repulsive c ores of the vortices. We present results for a Ginzburg-Landau suscept ibility kappa=72 as appropriate for YBa2Cu3O7-y (YBCO). The competitio n between the entropic term due to excluded volume effects and the rep ulsive vortex-vortex interactions determines, in our model, the coexis tence of both a solid and a fluid phase. The corresponding melting tra nsition exhibits a reentrant behavior, in agreement with previous theo retical works and has a very weak first-order character.