Inter-layer phase difference and flux-line entanglement at first-order melting transition of high-T-c vortex systems

The mechanism of the flux-line-lattice melting in high-T-c superconductors is investigated numerically. The percentage of entangled flux lines abruptl y increases at the melting temperature T-m, which indicates that this excit ation is the origin of the melting transition. The one-dimensional size dep endence of T-m ensures this picture. The inter-layer phase difference sharp ly jumps at T-m, which is consistent with the Josephson plasma resonance ex periment. This jump is scaled by the anisotropy constant and the flux-line density for a wide range of parameters. For extremely large anisotropy, thi s jump saturates and becomes as large as those observed experimentally.