Unusually High Critical Current Of Clean P-Doped Bafe2as2 Single Crystalline Thin Film

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/cm(2) at 4.2 K, which are among the highest for Fe based superconductors (FeSCs). In-field J(c) exceeds 0.1 MA/cm(2) at mu H-0 = 35 T for H parallel to ab and mu H-0 = 18 T for H parallel to 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. (C) 2015 AIP Publishing LLC.