Jong-Hoon Kang1 Jong-Woo Kim2 Phillip Ryan2 Lu Guo1 Chirs Sundahl1 Jonathon Schad1 Y.G. Collantes3 Hellstrom Eric3 David Larbalestier3 Chang-Beom Eom1

1, University of Wisconsin, Madison, Wisconsin, United States
2, Argonne National Laboratory, Argonne, Illinois, United States
3, University of Florida, Tallahassee, Florida, United States

Significant progress has been made in fabricating high-quality epitaxial thin films of iron-based superconductors. Strain engineering offers the possibility of tailoring the structural distortions at the atomic scale and enhancing superconducting properties. Here, we report that tetrahedral geometry driven by thin film strain leads to a significant enhancement of the superconducting transition temperature (Tc) of optimal Co-doped epitaxial BaFe2As2 thin films above the value of the bulk single crystals. We have found that the As-Fe-As bond angles were strongly modified by both epitaxial and thermal strains caused by the temperature-dependent lattice mismatch between BaFe2As2 thin films and the substrates. Synchrotron x-ray diffraction and resonant scattering demonstrate that the As-Fe-As bond angle and Tc are systematically tuned by in-plain strain and reach maximum Tc at the optimum bond angle of 109.5o. Strain engineering can provide a path toward tailoring superconducting properties and understanding superconductivity in other Fe-based superconducting thin films such as monolayer FeSe.

This work has been done in collaboration with J. H. Kang, P. J. Ryan, J. W. Lee, J. W. Kim, Y. Choi, J. Jiang, E. E. Hellstrom, D. C. Larbalestier.

** This was supported by the DOE Office of Basic Energy Sciences under award number DE-FG02-06ER46327.