Local Atomic Configuration Control of Superconductivity in BaFe₂As₂ Pnictide

Doped Fe-based superconductors show broken-symmetry phases coexisting with superconductivity, and determined by structural distortions of the local tetrahedral geometry. The tetragonal-to-orthorhombic phase transition of the parent materials however make these structural deformations too complex to be predictably controlled by chemical doping or hydrostatic pressure in bulk systems. We demonstrate a systematic approach to manipulate the local structural configurations in epitaxial thin films of the nominally non-superconducting parent material BaFe₂As₂by controlling two independent structural factors: orthorhombicity (in-plane anisotropy) and tetragonality (out-of-plane/in-plane balance). We generate and tune superconductivity without chemical doping by using these to control the local tetrahedral coordination in designed thin film heterostructures with substrate clamping and bi-axial strain. We further show that this allows control the structural phase transition, associated magnetism, and superconductivity in the parent material BaFe₂As₂. This approach will advance the development of tunable thin film superconductors in reduced dimension.<br/>This work has been done in collaboration with J. H. Kang, P. J. Ryan, J.W. Kim, J. Schad, J. P. Podkaminer, N. Campbell, J. Suttle, T. H. Kim, L. Luo, D. Cheng, Y. G. Collantes, E. E. Hellstrom, J. Wang, R. McDermott, M. S. Rzchowski.<br/>This work was supported by the US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, (DE-FG02-06ER46327).