Charge transfer and local structure distortion in Zn-doped LaFe1−xCoxAsO

To understand the significant suppression of the superconducting transition temperature Tc by non-magnetic Zn impurity, Zn doping effect on the electronic structure and local structure distortion for the superconductor LaFe1−x−yCoxZnyAsO have been investigated by X-ray absorption spectroscopy (XAS). Fe and As K-edge X-ray absorption near-edge spectroscopy (XANES) point out the charge distribution between Fe and As atoms in the presence of Zn impurities. Moreover, doping by Zn impurities the local lattice structure is finely modulated probed by Fe and As extend X-ray absorption fine structure (EXAFS). With Zn doping the FeAs bond is rigid, while the distance of FeFe pairs increases. That leads to a more distorted FeAs4 tetrahedron in the presence of Zn impurities. Therefore, in LaFe1−xCoxZnyAsO system the severe suppression of Tc by Zn impurity is mostly associated with the more distorted FeAs4 tetrahedron.