Simulation for the first-order vortex-lattice melting transition in high-T-c superconductors

Monte Carlo simulations are performed to investigate vortex states in high-T-c, superconductors. Latent heat and delta-function like divergence in the specific heat are observed as the vortex-line lattice is melt into a liquid of pancake vortex. As the anisotropy is reduced, another transition between the liquid of vortex line and that of pancake vortex is found associated with large thermal fluctuations and a weak latent heat. In relation to the vortex line liquid in systems with columnar defects, the results for smaller anisotropy are discussed. A crossover to a pancake vortex gasphase at an even higher temperature is observed as the trajectory of the mean-field phase boundary H-c2.