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

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).