Comment on "Isoelectronic Ru substitution at Fe-site in Sm(Fe$_{1-x}$Ru$_x$)AsO$_{0.85}$F$_{0.15}$ compound and its effects on structural, superconducting and normal state properties" (arXiv:1004.1978)

TL;DR

This paper discusses impurity scattering effects in Ru-substituted Sm(Fe,Ru)AsO compounds, showing that increased impurity scattering suppresses the superconducting $s_$-wave state, with implications for interpreting magnetoresistance data.

Contribution

It provides a theoretical analysis of impurity scattering rates in Ru-doped iron-based superconductors, highlighting the suppression of the $s_$-wave state at certain impurity levels.

Findings

Impurity scattering rate increases with Ru substitution.

Superconducting $T_c$ decreases as impurity scattering rises.

Magnetoresistance may underestimate impurity scattering in correlated systems.

Abstract

Based on the five-orbital model, we derive the reduced impurity scattering rate $g=z\gamma/2\pi T_{c0}$ in Sm(Fe$_{1-x}$Ru$_{x}$)AsO$_{0.85}$F$_{0.15}$ from the residual resistivity. At $x=0$, the transition temperature is $T_{c0}=50$ K. For $0.05<x<0.36$ ($0.84>T_{c}/T_{c0}>0.3$) the obtained value of $g$ ranges from 1.5 to 2.9, which suggests that the $s_\pm$-wave state cannot survive. We point out that the magnetoresistance frequently gives an underestimated value of $g$ in correlated electron systems.