Effects of Point Defects Introduced by Co-doping and Proton Irradiation in CaKFe4As4

Abstract

Introduction of point defects into superconductors through proton irradiation enhances their critical current density (J _c). Similarly, chemical doping can also produce point defects, leading to the enhancement of J _c. Iron-based superconductors (IBSs) have been investigated as promising materials for practical applications because of their large J _c at high magnetic fields and temperatures. Recently, another promising IBS CaKFe₄As₄ (1144-type) was found, and attracts much interest due to its characteristic feature such as stoichiometric superconductivity and the presence of novel planar defects. We have grown single crystals of Co-doped CaKFe₄As₄ and clarified the effect of chemically-introduced point defects on J _c. We also introduced point defects through 3 MeV proton irradiation, and compared the effect of point defects to J _c.