Zn-impurity effect and interplay of $s_{\pm }$- and $s_{++}$-pairings in Fe-based superconductors

Abstract

We report theoretical and experimental studies of the effect of Zn-impurity in Fe-based superconductors. Zn-impurity is expected to severely suppress sign reversed s${}_{\pm }$ wave pairing. The experimentally observed suppression of T${}_c$ under Zn-doping strongly depends on the materials and the charge carrier contents, which suggests competition of $s_{++}$ and $s_{\pm }$ pairings in Fe-base superconductors. We study a model incorporating both $s_{++}$ and $s_{\pm }$ pairing couplings by using Bogoliubov de-Gennes equation, and show that the Zn-impurity strongly suppresses $s_{\pm }$ pairing and may induce a transition from $s_{\pm }$ to $s_{++}$-wave. Our theory is consistent with various experiments on the impurity effect. We present new experimental data on the Zn-doping SmFe${}_{1-x}$Zn${}_x$AsO${}_{0.9}$F${}_{0.1}$ of T${}_c=$ 50K, in further support of our proposal.

arXiv comment6 pages, 5 figures

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