Charge redistribution and local lattice structure of (F, Zn)-codoped LaFeAsO superconductor

Jie Cheng,Yuke Li,Ziyu Wu,Rong Hu,Zhu-An Xu,Augusto Marcelli,Wei Xu,Linjuan Zhang,Jing Zhou,Wangsheng Chu

doi:10.1088/1367-2630/14/3/033005

Abstract

To understand the abnormal behavior of the superconducting transition temperature (Tc) because of the presence of a non-magnetic Zn impurity in the (F, Zn)-codoped LaFeAsO system (Li et al 2010 New J. Phys.12 083008), we investigated its unique electronic and local structures via x-ray absorption spectroscopy and first-principles calculations. The data obtained showed that the presence of a Zn impurity induces an electron transfer from As to Fe atoms in both the F-underdoped and -overdoped regions. Moreover, due to the lattice mismatch, the local lattice structure is finely modulated by both F and Zn impurities. Actually, in the F-underdoped region doping by Zn is associated with regular FeAs4 tetrahedra, while distorted FeAs4 tetrahedra occur in the F-overdoped region where superconductivity is significantly suppressed.

Highlights

To understand the abnormal behavior of the superconducting transition temperature (Tc) because of the presence of a non-magnetic Zn impurity in the (F, Zn)-codoped LaFeAsO system
It is well known that F atoms select an O site in LaFeAsO1−x Fx [1], for doped compounds, in particular in the codoped system, the first issue is to identify the occupation site of the dopant
Data support a scenario in which Zn ions are embedded in the LaFeAsO1−x Fx matrix and Zn K-edge calculations with a Fe atom replaced by Zn successfully reproduce all x-ray absorption near edge spectroscopy (XANES) features, i.e. Zn occupies the Fe site

Summary

Introduction

To understand the abnormal behavior of the superconducting transition temperature (Tc) because of the presence of a non-magnetic Zn impurity in the (F, Zn)-codoped LaFeAsO system 12 083008), we investigated its unique electronic and local structures via x-ray absorption spectroscopy and first-principles calculations. Nuclear magnetic resonance and nuclear quadrupole resonance investigations in the Zn-substituted LaFeAsO0.85 system showed that Zn impurities do not affect the crystal structure and electronic states [19]. We present a combined study using x-ray absorption spectroscopy and first-principles electronic structure calculations of NMI substitutions in iron pnictides. In the proposed scenario of a charge redistribution and possible local lattice distortions, the goal of this research is to identify cooperative mechanisms among F and Zn ions in the (F, Zn)-codoped LaFeAsO system

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Conclusion