Probing antiferromagnetic order of iron-based superconductors through the surface*

Understanding the surface structural and electronic properties of iron-based superconductors (FeSCs) is of great significance, as it can reveal the bulk superconducting properties. Previous study reveals a state near 0.2eV below Fermi level on √2×√2 or 2×1 reconstructed surface of Ba(Fe1-xCox)2As2, which is identified as a surface state by ARPES and DFT calculations. This state has also been observed on the surfaces of other 122 FeSCs with different doping levels, alkaline earth metal elements, and surface reconstructions. Its common presence suggests an origin other than simple surface state. Here, we systematically investigated low-temperature cleaved parent and slightly doped BaFe2As2 superconductors by scanning tunneling microscopy/spectroscopy (STM/S). We observed the same state on all √2×√2, 2×1 and even mixed surfaces. However, it vanishes when heating the sample above the Neel temperature (TN), and recovers after cooling down below TN, suggesting it is related to the bulk antiferromagnetic order.