MONTE-CARLO SIMULATION ON THE FIRST-ORDER MELTING TRANSITION OF HIGH-T-C SUPERCONDUCTORS IN B-PARALLEL-TO(C)OVER-CAP

The first-order melting transition of the vortex-line lattice of high- T-c superconductors in B parallel to (c) over cap is investigated by M onte Carlo simulation based on the three-dimensional uniformly frustra ted, anisotropic XY model. A delta-function peak in the specific heat is observed at the melting point T-m associated with a latent heat, wh ere the triangular vortex-line lattice melts. A jump in the helicity m odulus along the c axis is observed at the melting point from zero to 16 pi(3)lambda(ab)(2)(T-m)Y-c(T-m)Gamma(2)/(d phi(0)(2)) similar or eq ual to 0.6 with Gamma the anisotropy constant in the present model. Th erefore, the system is superconducting only below T-m and along the c axis. There is, however, short-range correlation between Vortices both along the c axis and in the ab plane, and therefore the system behave s as a liquid of vortex lines, in the Vicinity above the melting point for the anisotropy constants studied. The simulation gives estimates on the jumps of entropy and magnetic induction on the melting in good agreement with the experimental observation on a YBa2Cu3O7-delta singl e crystal. Although the agreement is not as good as with the YBa7Cu3O7 -delta sample, the simulation results are comparable with the experime ntal observation on a Bi2Sr2CaCu2O8 sample. The simulated melting line in the B-T diagram is fitted very well by B-m=0.132 x{d phi(0)(2)/[16 pi(3)lambda(ab)(2)(T-m)k(B)T(m)]}(2), which coincides with the meltin g theory based on a continuum description of the vortex-line lattice c ombined with the Lindemann criterion taking c(L)= 0.18.