K-Doped BaFe₂As₂ / BaFe₂As₂ Bilayer for Bi-Crystal Experiments

Bilayer composed of parent and doped compounds creates a clean and sharp interface due to the chemically inert each layer. Herein, we report on the sharp interface between K-doped BaFe₂As₂ (Ba122) and the parent compound Ba122 grown by molecular beam epitaxy. Structural and microstructural analysis revealed that K did not diffuse into the parent Ba122. The bilayer K-doped Ba122/Ba122 exhibited a high superconducting transition temperature <i>T</i>_c of 40 K, which is higher than K-doped Ba122 grown on CaF₂(001) (<i>T</i>_c~33 K) [1-2] due to the suppression of strain. We also demonstrate that K-doped Ba122/Ba122 is grown on symmetric [001]-tilt MgO bi-crystal substrates having different misorientation angles <i>θ</i>_GB. We will discuss the microstructure and superconducting properties of the bilayer K-doped Ba122/Ba122.<br/>This work was supported by JST CREST Grant Number JPMJCR18J4. A portion of work was performed at the National Magnetic Field Laboratory, which was supported by National Science Foundation Cooperative Agreement No. DMR-1644779, US Department of Energy Office of High Energy Physics under the grant number DE-SC0018750, and the State of Florida. This work was also partly supported by Advanced Characterization Platform of the Nanotechnology Platform Japan sponsored by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.<br/>[1] D. Qin, K. Iida, T. Hatano, H. Saito, Y. Ma, C. Wang, S. Hata, M. Naito, A. Yamamoto, <i>Phys. </i><i>Rev. Mater</i>. <b>5</b>, 014801 (2021).<br/>[2] K. Iida, D. Qin, C. Tarantini, T. Hatano, C. Wang, Z. Guo, H. Gao, H. Saito, S. Hata, M. Naito, A. Yamamoto, <i>NPG. Asia Mater</i>. <b>13</b>, 68 (2021).