Co-substitution effects on the Fe-valence in the BaFe2As2 superconducting compound: A study of hard x-ray absorption spectroscopy

TL;DR

This study uses X-ray absorption spectroscopy to examine how cobalt substitution affects the electronic structure of BaFe2As2 superconductors, revealing that Co does not alter Fe valence but may influence superconductivity through bonding modifications.

Contribution

It provides experimental evidence that Co substitution does not change Fe valence in BaFe2As2, supporting ab initio calculations and suggesting alternative mechanisms for superconductivity emergence.

Findings

Co substitution does not alter Fe K-edge energy or shape.

Extra Co electrons are localized at the substitution site.

Superconductivity may be linked to bonding changes rather than Fe valence shifts.

Abstract

The Fe K X-ray absorption near edge structure (XANES) of BaFe2-xCoxAs2 superconductors was investigated. No appreciable alteration in shape or energy position of this edge was observed with Co substitution. This result provides experimental support to previous ab initio calculations in which the extra Co electron is concentrated at the substitute site and do not change the electronic occupation of the Fe ions. Superconductivity may emerge due to bonding modifications induced by the substitute atom that weakens the spin-density-wave ground state by reducing the Fe local moments and/or increasing the elastic energy penalty of the accompanying orthorhombic distortion.