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

TL;DR

This study uses Monte Carlo simulations of the 3D frustrated XY model to reveal that flux-line entanglement drives the melting transition of the flux-line lattice in high-temperature superconductors under a magnetic field.

Contribution

It demonstrates that flux-line entanglement, rather than vortex loop distributions, is the key mechanism for FLL melting, supported by scaling behaviors and Lindemann number evaluation.

Findings

Abrupt increase in flux-line entanglement at melting temperature

No sharp change in vortex loop distribution at T_m

Scaling behaviors support entanglement-driven melting mechanism

Abstract

The mechanism of the flux-line-lattice (FLL) melting in anisotropic high-T_c superconductors in ${\bf B}\parallel {\bf \hat{c}}$ is clarified by Monte Carlo simulations of the 3D frustrated XY model. The percentage of entangled flux lines abruptly changes at the melting temperature T_m, while no sharp change can be found in the number and size distribution of vortex loops around T_m. Therefore, the origin of this melting transition is the entanglement of flux lines. Scaling behaviors of physical quantities are consistent with the above mechanism of the FLL melting. The Lindemann number is also evaluated without any phenomenological arguments.