Unique defect structure and advantageous vortex pinning properties in superconducting CaKFe4As4

TL;DR

This study uncovers unique defect structures in CaKFe4As4 that lead to exceptional vortex pinning and high critical current densities, advancing its potential for high-field superconducting applications.

Contribution

It reveals the inherent nanoscale intergrowth defect structures in CaKFe4As4 and explains their role in enhancing vortex pinning and critical current density.

Findings

Nanoscale intergrowths of CaFe2As2 are present in CaKFe4As4.

CaKFe4As4 exhibits high anisotropic Jc properties.

Pinning mechanism is significantly enhanced with temperature.

Abstract

The lossless current-carrying capacity of a superconductor is limited by its critical current density (Jc). A key to enhance Jc towards real-life applications is engineering defect structures to optimize the pinning landscape. For iron-based superconductors (IBSs) considered as candidate materials for high-field applications, high Jc values have been achieved by various techniques to introduce artificial pinning centres. Here we report extraordinary vortex pinning properties in CaKFe4As4 (CaK1144) arising from the inherent defect structure. Scanning transmission electron microscopy revealed the existence of nanoscale intergrowths of the CaFe2As2 phase, which is unique to CaK1144 formed as a line compound. The Jc properties in CaK1144 are found to be distinct from other IBSs characterized by a significant anisotropy with respect to the magnetic field orientation as well as a remarkable pinning mechanism significantly enhanced with increasing temperature. We propose a comprehensive explanation of the Jc properties based on the unique intergrowths acting as pinning centres.