Phase Transitions of the Flux Line Lattice in High-Temperature Superconductors with Weak Columnar and Point Disorder

TL;DR

This paper investigates how weak point and columnar disorder influence phase transitions in the vortex lattice of high-temperature superconductors, revealing opposite effects on the melting line and the role of replica symmetry breaking in vortex glass formation.

Contribution

It introduces a simplified cage model to analyze the combined effects of thermal fluctuations and quenched disorder on vortex-lattice phase transitions.

Findings

Point disorder shifts the melting line differently than columnar disorder.

Replica symmetry breaking occurs at the vortex glass transition at low temperatures.

Point and columnar disorder have opposite effects on the vortex lattice phase diagram.

Abstract

We study the effects of weak point and columnar disorder on the vortex-lattice phase transitions in high temperature superconductors. The combined effect of thermal fluctuations and of quenched disorder is investigated using a simplified cage model. For point disorder we use the mapping to a directed polymer in a disordered medium in 2+1 dimensions. For columnar disorder the problem is mapped into a quantum particle in a harmonic + random potential. We use the variational approximation to show that point and columnar disorder have an opposite effect on the position of the melting line as is observed experimentally. For point disorder, replica symmetry breaking plays a role at the transition into a vortex glass at low temperatures.