Template engineering of co-doped BaFE₂As₂single-crystal thin films

Understanding new superconductors requires high-quality epitaxial thin films to explore intrinsic electromagneti properties and evaluate device applications1–9. So far, superconducting properties of ferropnictide thin films seem compromised by imperfect epitaxial growth and poor connectivity of the superconducting phase10–14. Here we report new template engineering using single-crystal intermediate layers of (001) SrTiO3 and BaTiO3 grown on various perovskite substrates thatenables genuine epitaxial films of Co-doped BaFe2As2 with a high transition temperature (T_c,ρ=0 of 21.5 K, where ρ = resistivity), a small transition width (δT_c= 1.3 K), a superior critical current density J_cof 4.5 MA cm⁻²(4.2 K) and strong c-axis flux pinning. Implementing SrTiO₃or BaTiO₃templates to match the alkaline-earth layer in the Ba-122 withthe alkaline-earth/oxygen layer in the templates opens new avenues for epitaxial growth of ferropnictides on multifunctional single-crystal substrates. Beyond superconductors, it provides a framework for growing heteroepitaxial intermetallic compounds on various substrates by matching interfacial layers between templates and thin-film overlayers.