Unusually high critical current of clean P-doped BaFe₂As₂ single crystalline thin film Available to Purchase

Microstructurally clean, isovalently P-doped BaFe₂As₂ (Ba-122) single crystalline thin films have been prepared on MgO (001) substrates by molecular beam epitaxy. These films show a superconducting transition temperature (T_c) of over 30 K although P content is around 0.22, which is lower than the optimal one for single crystals (i.e., 0.33). The enhanced T_c at this doping level is attributed to the in-plane tensile strain. The strained film shows high transport self-field critical current densities (J_c) of over 6 MA/cm² at 4.2 K, which are among the highest for Fe based superconductors (FeSCs). In-field J_c exceeds 0.1 MA/cm² at $μ0H=35 T$ for $H‖ab$ and $μ0H=18 T$ for $H‖c$ at 4.2 K, respectively, in spite of moderate upper critical fields compared to other FeSCs with similar T_c. Structural investigations reveal no defects or misoriented grains pointing to strong pinning centers. We relate this unexpected high J_c to a strong enhancement of the vortex core energy at optimal T_c, driven by in-plane strain and doping. These unusually high J_c make P-doped Ba-122 very favorable for high-field magnet applications.