Atomic and electronic structures of ternary iron arsenides AFe₂As₂(001) surfaces (A=Ba, Sr, or Ca)

الأصل · EN

By the first-principles electronic structure calculations, we find that energetically the most favorable cleaved AFe₂As₂(001) surface (A=Ba, Sr, or Ca) is A-terminated with a (√2× √2)R45∘ or (1× 2) order. The (1× 2) ordered structure yields a (1× 2) dimerized STM image, in agreement with the experimental observation. The A atoms are found to diffuse on the surface with a small energy barrier so that the cleaving process may destroy the A atoms ordering. At the very low temperatures this may result in an As-terminated surface with the A atoms in randomly assembling. The As-terminated BaFe₂As₂ surface in orthorhombic phase is (√2×√2)R45∘ buckled, giving rise to a switchable (√2× √2)R45∘ STM pattern upon varying the applied bias. No any reconstruction is found for the other As-terminated surfaces. There are surface states crossing or nearby the Fermi energy in the As-terminated and (1× 2) A-terminated surfaces. A unified physical picture is thus established to help understand the cleaved AFe₂As₂(001) surfaces.