Large and significantly anisotropic critical current density induced by planar defects in CaKFe4As4 single crystals

TL;DR

This study investigates the anisotropic critical current densities in CaKFe4As4 single crystals, revealing the influence of unique planar defects on superconducting properties and critical current behavior.

Contribution

It reports the discovery of planar defects in CaKFe4As4 and their correlation with highly anisotropic critical current densities, a novel finding in iron-based superconductors.

Findings

Observation of fish-tail-like peaks in M-H loops for H//c

Detection of a dip structure in M-H loops for H//ab

Successful evaluation of anisotropic in-plane and out-of-plane Jc

Abstract

Three independent components of critical current density, one for the H//c axis and the other two for the H//ab plane, have been studied in CaKFe4As4 single crystals. When the magnetic field is applied along the c axis, we observed fish-tail-like peaks in the M-H hysteresis loop, and the magnetization at higher temperatures exceeds that at lower temperatures at high fields. When the field is applied parallel to the ab plane, a dip structure is observed in the M-H hysteresis loop near the self-field. In addition, for the H//ab plane, we succeeded in separately evaluating the large and significantly anisotropic in-plane and out-of-plane Jc. Transmission electron microscopy revealed the presence of planar defects parallel to the ab plane in CaKFe4As4, which have not been observed in any other iron-based superconductors. We discuss the possible relationship between the anomalous Jc behavior and the planar defects.