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)

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.

2 pages

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