Co-Substitution Effects on the Fe Valence in theBaFe2As2Superconducting Compound: A Study of Hard X-Ray Absorption Spectroscopy

Abstract

The Fe K x-ray absorption near edge structure of BaFe(2-x)Co(x)As(2) 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.

A view from inside iron-based superconductors

“…However, as far as the substitution of the Fe ions with other transition metal (TM) elements is considered, the effectiveness of charge doping is still under strong debate and has been subject of recent intense efforts both on the computational and on the experimental sides, particularly in the case of Co for Fe substitution. Contrasting results have been reported from densityfunctional theory (DFT) calculations [37,38] as well as from measurements via x-rays absorption [39,40] and photoemission [41] spectroscopies. At the same time, the role of isovalent substitutions such as Fe 1−x Ru x attracted great interest both in LnFeAsO 1−x F x (the so-called 1111 family of IBS, with Ln a lanthanide ion) and in the AFe 2 As 2 (the 122 IBS, with A an alkali ion) compounds.…”

High-pressure flux growth, structural, and superconducting properties ofLnFeAsO (Ln=Pr, Nd, Sm) single cryst

“…Whether or not Co substitution is able to charge dope the Fe ions is a major issue that may help to identify the specific mechanism of superconductivity in Fe-based pnictides. For the case of Co substituted BaFe 2 As 2 , the lack of a Fe K edge absorption shift implies that Co is not charge doping the Fe ions, which are thought to be responsible for the superconductivity [57]. Rather it was argued that superconductivity may emerge due to bonding modifications induced by the substitute atom that weakens the spin-density-wave ground state by reducing reduced with respect to the pure compound.…”

“…There are still extended debates in the literature on the role of Co in inducing superconductivity in Fe-based pnictides [55][56][57][58][59]. Naturally, the Co substituted systems have been widely referred to as electron-doped.…”

Enhanced low-energy magnetic excitations via suppression of the itinerancy in Fe0.98−zCuzTeWen1, Li2, Xu3 et al. 2013Phys. Rev. B186210View full textAdd to dashboardCite

“…1,4,5 Such approaches typically describe the doping effects based on a rigid-band-shift model. [6][7][8] However, such a model has faced serious challenges from both the experimental and theoretical perspectives, 2,3,[9][10][11] each of which indicates the inadequacy of a rigid-band description. Furthermore, there is a dichotomy between Co/Ni and Cu substitution effects in terms of the emergence of the superconductivity.…”