K-doped Ba122 epitaxial thin film on MgO substrate by buffer engineering

Abstract Molecular beam epitaxy of K-doped Ba122 (Ba 1− x K x Fe 2 As 2 ) superconductor was realized on an MgO substrate. Microstructural observation revealed that the undoped Ba122 served as a perfect buffer layer for epitaxial growth of the K-doped Ba122. The film exhibited a high critical temperature of 39.8 K and a high critical current density of 3.9 MA cm −2 at 4 K. The successful growth of epitaxial thin film will enable artificial single grain boundary on oxide bicrystal substrates and reveal the grain boundary transport nature of K-doped Ba122.