Effects of swift-particle irradiation on CaKFe₄As₄ single crystals

CaKFe₄As₄ is a newly found iron-based superconductor with T_c~36 K, which has a similar crystal structure to BaFe₂As₂ with ordered Ca and K layers. We study effects of artificial defects created by heavy-ion irradiation on the critical current (J_c) in CaKFe₄As₄ single crystals that are irradiated by 800 MeV Xe ions up to the matching field (B_Φ) of 64 T. At 2 K, the self-field J_c for the pristine crystal is over ~1.5 MA/cm². However, it is reduced by a factor of ten at 50 kOe. We occasionally observe non-monotonic temperature dependence of J_c at high fields, which could be explained by the presence of field-induced pinning centers. J_c is enhanced monotonically with increasing B_Φ, and it reaches over 10 MA/cm² at 2 K and B_Φ = 16 T. The general behavior of J_c-B_Φ in CaKFe₄As₄ is similar to that in Xe-irradiated (Ba,K)Fe₂As₂.