Temperature dependent local atomic displacements in Ru substituted SmFe_{1-x}Ru_{x}AsO_{0.85}F_{0.15} superconductors

TL;DR

This study investigates how temperature and Ru substitution affect local atomic displacements in SmFe_{1-x}Ru_{x}AsO_{0.85}F_{0.15} superconductors, revealing phase coexistence and stable Fe-As bonds despite disorder.

Contribution

It provides detailed insights into local structural changes and disorder effects caused by Ru substitution in Fe-based superconductors using temperature-dependent EXAFS.

Findings

Ru substitution affects static disorder beyond x=0.25

Fe-As bond strength remains unchanged with Ru substitution

Ru-As and Fe-As distances show different behaviors

Abstract

Local structure of SmFe$_{1-x}$Ru$_x$AsO$_{0.85}$F$_{0.15}$ ($x$ = 0.0, 0.05, 0.25 and 0.5) superconductors has been investigated by temperature dependent As $K$-edge extended x-ray absorption fine structure. The effect of Ru substitution remains confined to the iron-arsenide layer but neither the static disorder nor the Fe-As bond strength suffers any change for $x \le$ 0.25. With further Ru substitution the static disorder increases while the Fe-As bond strength remains unchanged. Also, the Ru-As distance ($\sim$2.42 \AA), different from the Fe-As distance ($\sim$2.39 \AA), does not show any change in its force constant with the Ru substitution. These observations suggest that the SmFe$_{1-x}$Ru$_x$AsO$_{0.85}$F$_{0.15}$ system breaks down to coexisting local electronic phases on isoelectric substitution in the active FeAs layer.