Flux-line entanglement as the mechanism of melting transition in high-temperature superconductors in a magnetic field

The mechanism of the flux-line-lattice (FLL) melting in anisotropic high-T- c, superconductors in B parallel to (c) over cap is clarified by Monte Carl o simulations of the three-dimensional frustrated XY model. The percentage of entangled flux lines abruptly changes at the melting temperature T-m, wh ile no sharp change can be found in the number and size distribution of vor tex loops around T-m. Therefore, the origin of this melting transition is t he entanglement of flux lines. Scaling behaviors of physical quantities are consistent with the above mechanism of the FLL melting. The Lindemann numb er is also evaluated without any phenomenological arguments. [S0163-1829(99 )50818-7].