Effect of a Zn impurity on T_c and its implication to pairing symmetry in LaFeAsO$_{1-x}$F$_x$

TL;DR

This study investigates how non-magnetic Zn impurities affect superconductivity in LaFeAsO$_{1-x}$F$_x$, revealing a doping-dependent change in T_c and suggesting a transition in pairing symmetry from s-wave to s$_{ ext{±}}$ or d-wave states.

Contribution

It provides systematic experimental evidence for a doping-dependent change in pairing symmetry in FeAs-based superconductors due to Zn impurity effects.

Findings

T_c increases in under-doped regime with Zn impurity

T_c remains unchanged in optimally doped regime

T_c is suppressed in over-doped regime

Abstract

The effect of non-magnetic Zn impurity on superconductivity in LaFe$_{1-y}$Zn$_y$AsO$_{1-x}$F$_x$ system is studied systematically. In the presence of Zn impurity, the superconducting transition temperature increases in the under-doped regime, remains unchanged in the optimally doped regime, and is severely suppressed in the over-doped regime. Our results suggest a switch of the symmetry of the superconducting order parameters from a $s$-wave to $s_{\pm}$ or $d$-wave states as the charge carrier doping increases in FeAs-based superconductors.