Origin of Weak-Link Behavior of Grain Boundaries in Superconducting Cuprates and Pnictides

TL;DR

This paper investigates the weak-link behavior of grain boundaries in high-temperature superconductors, proposing a bond contraction pairing model that links atomic displacements to critical current reduction and vortex pinning.

Contribution

It introduces a bond contraction pairing model explaining how atomic bond deformations at grain boundaries affect superconductivity in cuprates and pnictides.

Findings

Reduced critical current at low angle grain boundaries is due to tensile deformation from dislocations.

Interface misfit dislocations can enhance vortex pinning, contrary to creating dead layers.

The model links atomic-scale bond contractions to macroscopic superconducting properties.

Abstract

Superconducting cuprates and pnictides composed of CuO2 or AsFe planes respectively with intercalated insulating layers, are at the crossroads of three families of crystalline solids: metals, doped Mott insulators, and ferroelectrics. In the latter atomic displacements play a key role. Both the metallic and the doped insulator approaches to high temperature superconductivity are essentially electronic ones and do not directly involve the lattice. By contrast, in a recently proposed Bond Contraction Pairing (BCP) model, contraction of in-plane Cu-O (or As-Fe) bonds plays an essential role in the pairing mechanism. Here we apply it to low angle grain boundaries and show that their reduced critical current is due to tensile deformation generated by dislocations. The model also explains why interface misfit dislocations, which can result in a dead layer in the case of ferro-electrics, may improve vortex pinning in the cuprates.