Strikingly dissimilar effect of Mn and Zn dopants imposed on local structural distortion of Ba_0.5K_0.5Fe₂As₂ superconductor

To clarify the contrasting impurity effects of Mn and Zn dopants on the critical temperature of optimally doped Ba_0.5K_0.5Fe₂As₂ superconductors, extended X-ray absorption fine-structure spectroscopy was implemented at the Fe and As K-edge. In Mn-doped compounds a gradual deviation of the symmetric FeAs₄ tetrahedron and weakening of the Fe-As bond was observed. Conversely, in Zn-doped compounds the perfect FeAs₄ tetrahedron is maintained and the Fe-As bond is rigid. The local structural details are consistent with the development of superconductivity in these two systems, suggesting a significant role played by the topology of the FeAs₄ tetrahedron and rigidness of the Fe-As bond in Mn/Zn-doped Ba_0.5K_0.5Fe₂As₂ superconductors.