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 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 iron-based superconductors 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.
Highlights
The crystal structure of the CaK1144 matrix and the unique defect structure can be directly observed by high-resolution scanning transmission electron microscopy (STEM) experiments
Regarding H // c, the H and T dependence of Jc for H // c (JcH//c) of CaK1144 is visualized in the form of a npj Quantum Materials (2019) 27
It is found that the peak in JcH//c–T (Tp) is almost H-independent, suggestive of a unique origin of the enhanced pinning with increasing T
Summary
Loss-free electrical transport is a unique property of superconductors that is utilized in various superconductivity applications. How to design and introduce defects is one of the key issues towards real-life applications. Various techniques have been developed to control defect structures, through the research on high-transitiontemperature (high-Tc) cuprate superconductor YBa2Cu3O7 (YBCO) thin films.[2–5]. Controlled artificial defects can be created by particle irradiation,[10–12] this technique needs complex and dedicated facilities. Various techniques have been exploited to introduce artificial defects in iron-based superconductors (IBSs) since their discovery.[13,14]. As in the case of YBCO, Jc has been enhanced for AEFe2As2-based (AE: alkaline-earth element) superconductors, the so-called 122 materials, by particle irradiation,[15] addition of BaZrO3,16,17 fabrication of superlattices,[18] and introduction of stacking faults.[19,20]. By devising the fabrication process, a significant progress has been achieved in improving Jc of bulks and thin films so far, while further Jc enhancement is required towards real-life applications Various techniques have been exploited to introduce artificial defects in iron-based superconductors (IBSs) since their discovery.[13,14] As in the case of YBCO, Jc has been enhanced for AEFe2As2-based (AE: alkaline-earth element) superconductors, the so-called 122 materials, by particle irradiation,[15] addition of BaZrO3,16,17 fabrication of superlattices,[18] and introduction of stacking faults.[19,20] By devising the fabrication process, a significant progress has been achieved in improving Jc of bulks and thin films so far, while further Jc enhancement is required towards real-life applications
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