Phase diagram of vortices in high-Tc superconductors from lattice defect model with pinning

Abstract

The theory presented is based on a simple Hamiltonian for a vortex lattice in a weak impurity background which includes linear elasticity and plasticity, the latter in the form of integer valued fields accounting for defects. Within a quadratic approximation in the impurity potential, we find a first-order Bragg-glass, vortex-glass transition line showing a reentrant behavior for superconductors with a melting line near Hc2. Going beyond the quadratic approximation by using the variational approach of Mézard and Parisi established for random manifolds, we obtain a phase diagram containing either a first-order or a third-order glass transition line depending on the form of the disorder potential. Disorder potentials resulting in a unified glass transition line of a third-order part (high magnetic fields) and a first-order part (low magnetic fields) are possible. The glass transition line separates the vortex glass and the vortex liquid. Furthermore, we find a unified first-order line consisting of the melting transition between the Bragg glass and the vortex liquid phase as well as a disorder induced first-order line between the Bragg glass and the vortex glass phase. The reentrant behavior of this line within the quadratic approach mentioned above vanished. We calculate the entropy and magnetic induction jumps over the first-order line.

Source-reported materials — not catalogue approval

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