Impact of Local Atomic Fluctuations on Superconductivity of Pr-Substituted CaFe₂As₂ Studied by X-ray Fluorescence Holography

Abstract

The local structures of Ca1−xPrxFe2As2 (\(x = 0,0.1\)) were studied by X-ray fluorescence holography. Significant fluctuations were observed in As positions for CaFe2As2. The fluctuations increased strongly around Ca atoms by Pr substitution, while those around the substituted Pr atoms were largely unchanged. The inherent positional fluctuations of As in CaFe2As2 can be related to the various bonding forms of As and the complex structure with many energy minima suggested from the single-crystal and powder X-ray diffraction experiments. In the Pr-doped CaFe2As2, the increased and unchanged fluctuations around Ca and Pr atoms, respectively, could explain the local superconductivity around Pr atoms and its absence around Ca atoms suggested from scanning tunneling microscopy/spectroscopy.