Existence, character and origin of surface-related bands in the high temperature iron pnictide superconductor BaFe_2-xCo_xAs₂

Low energy electron diffraction (LEED) experiments, LEED simulations, and finite slab density functional calculations are combined to study the cleavage surface of Co doped BaFe2-xCoxAs2 (x=0.1,0.17). We demonstrate that the energy dependence of the LEED data can only be understood from a terminating 1/2 Ba layer accompanied by distortions of the underlying As-Fe2-As block. As a result, surface-related Fe 3d states are present in the electronic structure, which we identify in angle resolved photoemission spectroscopy (ARPES) experiments. The close proximity of the surface-related states to the bulk bands inevitably leads to broadening of the ARPES signals, which excludes the use of the BaFe2-xCoxAs2 system for accurate determination of self-energies using ARPES.