Impurity effect and suppression to superconductivity in Na(Fe$_{0.97-x}$Co$_{0.03}$T$_x$)As (T=Cu, Mn)

TL;DR

This study investigates how Cu and Mn impurities affect superconductivity in Na(Fe,Co)As crystals, revealing that non-magnetic Cu suppresses superconductivity more rapidly than magnetic Mn, challenging conventional impurity effects.

Contribution

It provides detailed experimental analysis of impurity effects on superconductivity, showing magnetic impurities can be less detrimental than non-magnetic ones in this system.

Findings

Cu doping weakens magnetic moments, Mn doping enhances them.

Both impurities increase residual resistivity and suppress superconductivity.

Mn impurities allow superconductivity to persist at higher resistivity levels.

Abstract

We report the successful growth and the impurity scattering effect of single crystals of Na(Fe$_{0.97-x}$Co$_{0.03}$T$_x$)As (T=Cu, Mn). The temperature dependence of DC magnetization at high magnetic fields is measured for different concentrations of Cu and Mn. Detailed analysis based on the Curie-Weiss law indicates that the Cu doping weakens the average magnetic moments, while doping Mn enhances the local magnetic moments greatly, suggesting that the former may be non- or very weak magnetic impurities, and the latter give rise to magnetic impurities. However, it is found that both doping Cu and Mn will enhance the residual resistivity and suppress the superconductivity at the same rate in the low doping region, being consistent with the prediction of the S$^{\pm}$ model. For the Cu-doped system, the superconductivity is suppressed completely at a residual resistivity $\rho_0$ = 0.87 m$\Omega$ cm at which a strong localization effect is observed. However, in the case of Mn doping, the behavior of suppression to \emph{T}$_{c}$ changes from a fast speed to a slow one and keeps superconductive even up to a residual resistivity of 2.86 m$\Omega$ cm. Clearly the magnetic Mn impurities are even not as detrimental as the non- or very weak magnetic Cu impurities to superconductivity in the high doping regime.