Existence, character and origin of surface-related bands in the high temperature iron pnictide superconductor BaFe_{2-x}Co_{x}As_{2}

TL;DR

This study combines experimental and computational methods to analyze the surface structure of Co-doped BaFe_{2-x}Co_{x}As_{2} superconductors, revealing surface-related states that affect electronic measurements.

Contribution

It identifies the surface termination and associated distortions in BaFe_{2-x}Co_{x}As_{2} using LEED, simulations, and DFT, and links surface states to ARPES signal broadening.

Findings

Surface is terminated by a 1/2 Ba layer with distortions.

Surface states are present in Fe 3d orbitals.

Surface states cause ARPES broadening, complicating self-energy analysis.

Abstract

Low energy electron diffraction (LEED) experiments, LEED simulations and finite slab density functional calculations are combined to study the cleavage surface of Co doped BaFe_{2-x}Co_{x}As_{2} (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-Fe_2-As block. As a result, surface related Fe 3d states are present in the electronic structure, which we identify in angle resolved photoemission 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 BaFe_{2-x}Co_{x}As_{2} system for accurate determination of self-energies using ARPES.