Flux-line entanglement as the mechanism of FLL-melting transition in anisotropic HTSC

The mechanism of the flux-line-lattice (FLL) melting in anisotropic high-Tc superconductors in B parallel cflx c is clarified by Monte Carlo simulations of the 3D frustrated XY model. The percentage of entangled flux lines abruptly changes at the melting temperature Tm, while no sharp change can be found in the number and size distribution of vortex loops around Tm. Therefore, the origin of this melting transition is the entanglement of flux lines. Scaling behaviors of the melting temperature Tm are consistent with this one-dimensional character of the entanglement mechanism of the FLL melting. That is, Tm does not depend on the system size in the ab plane, while it is scaled by the system size along the c axis, Lc, as Tm(Lc) minus Tm(∞) ∝ Lc-d, d = 1