Abstract
Understanding new superconductors requires high-quality epitaxial thin films to explore intrinsic electromagnetic properties and evaluate device applications1,2,3,4,5,6,7,8,9. So far, superconducting properties of ferropnictide thin films seem compromised by imperfect epitaxial growth and poor connectivity of the superconducting phase10,11,12,13,14. Here we report new template engineering using single-crystal intermediate layers of (001) SrTiO3 and BaTiO3 grown on various perovskite substrates that enables genuine epitaxial films of Co-doped BaFe2As2 with a high transition temperature (Tc,ρ=0 of 21.5 K, where ρ=resistivity), a small transition width (ΔTc=1.3 K), a superior critical current density Jc of 4.5 MA cm−2 (4.2 K) and strong c-axis flux pinning. Implementing SrTiO3 or BaTiO3 templates to match the alkaline-earth layer in the Ba-122 with the 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.
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Acknowledgements
We are grateful to J. Fournelle, M. Putti, A. Xu, F. Kametani, A. Gurevich, P. Li and V. Griffin for discussions and experimental help. Work at the University of Wisconsin was supported by funding from the DOE Office of Basic Energy Sciences under award number DE-FG02-06ER46327, and that at the NHMFL was supported under NSF Cooperative Agreement DMR-0084173, by the State of Florida and by AFOSR under grant FA9550-06-1-0474. A.Y. is supported by a fellowship of the Japan Society for the Promotion of Science. All TEM work was carried out at the University of Michigan and was supported by the Department of Energy under grant DE-FG02-07ER46416.
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S.L. fabricated Ba-122 thin-film samples and prepared the manuscript. J.J. carried out electromagnetic characterization and prepared the manuscript. J.D.W. fabricated Ba-122 pulsed laser deposition targets for thin-film deposition. C.W.B., H.W.J., C.M.F. and J.W.P. fabricated thin-film templates on single-crystal substrates. C.T., A.P., D.A. and A.Y. carried out electromagnetic characterizations. S.H.B. and C.W.B. analysed epitaxial arrangement by X-ray diffraction. Y.Z. and C.T.N. carried out TEM measurements. C.B.E., D.C.L., E.E.H. and X.Q.P. supervised the experiments and contributed to manuscript preparation. C.B.E. designed and directed the research. All authors discussed the results and implications and commented on the manuscript at all stages.
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Lee, S., Jiang, J., Zhang, Y. et al. Template engineering of Co-doped BaFe2As2 single-crystal thin films. Nature Mater 9, 397–402 (2010). https://doi.org/10.1038/nmat2721
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DOI: https://doi.org/10.1038/nmat2721
