Atomically-flat, chemically-stable, superconducting epitaxial thin film of iron-based superconductor, cobalt-doped BaFe2As2

The epitaxial growth of Fe-based superconductors such as Co-doped SrFe2As2 (SrFe2As2:Co) was reported recently, but has still insufficient properties for a device application because they have rough surfaces and are decomposed by reactions with water vapor in an ambient atmosphere. This paper reports that epitaxial films of Co-doped BaFe2As2 grown at 700 ∘C show the onset superconducting transition temperature of ∼20 K. The transition is sharper than those observed on the SrFe2As2:Co films, which would originate from their improved crystallinity. These films also have atomically-flat surfaces with step-and-terrace structures and exhibit chemical stability against exposure to water vapor.