Cleavage surfaces of the BaFe2−xCoxAs2 and FeySe1−xTex superconductors: A combined STM plus LEED study

Abstract

We elucidate the termination surface of cleaved single crystals of the ${\text{BaFe}}_{2-x}{\text{Co}}_x{\text{As}}_2$ and ${\text{Fe}}_y{\text{Se}}_{1-x}{\text{Te}}_x$ families of the high-temperature iron-based superconductors. By combining scanning tunneling microscopic data with low-energy electron diffraction we prove that the termination layer of the ${\text{BaFe}}_2{\text{As}}_2$ systems is a remnant of the Ba layer, which exhibits a complex diversity of ordered and disordered structures. The observed surface topographies and their accompanying superstructure reflections in electron diffraction depend on the cleavage temperature. In stark contrast, ${\text{Fe}}_y{\text{Se}}_{1-x}{\text{Te}}_x$ possesses only a single termination structure—that of the tetragonally ordered ${\text{Se}}_{1-x}{\text{Te}}_x$ layer.