The drastic effect of the impurity scattering on the electronic and superconducting properties of Cu-doped FeSe

TL;DR

This study investigates how strong impurity scattering from Cu doping affects the electronic structure and superconductivity in FeSe, revealing rapid suppression of superconductivity and nematic order, and highlighting the role of impurity potential.

Contribution

It provides detailed insights into the impact of strong impurity potential on FeSe's electronic and superconducting properties, emphasizing the role of Cu substitution and strain effects.

Findings

Cu doping suppresses nematic and superconducting states

Residual resistivity increases due to impurity scattering

Charge carrier mobility decreases by a factor of ~3

Abstract

Non-magnetic impurities in iron-based superconductors can provide an important tool to understand the pair symmetry and they can influence significantly the transport and the superconducting behaviour. Here, we present a study of the role of strong impurity potential in the Fe plane, induced by Cu substitution, on the electronic and superconducting properties of single crystals of FeSe. The addition of Cu quickly suppresses both the nematic and superconducting states, and increases the residual resistivity due to enhanced impurity scattering. Using magnetotransport data up to 35 T for a small amount of Cu impurity, we detect a significant reduction in the mobility of the charge carriers by a factor of ~3. While the electronic conduction is strongly disrupted by Cu substitution, we identify additional signatures of anisotropic scattering which manifest in linear resistivity at low temperatures and $H^{1.6}$ dependence of magnetoresistance. The suppression of superconductivity by Cu substitution is consistent with a sign-changing $s_{\pm}$ order parameter. Additionally, in the presence of compressive strain, the superconductivity is enhanced, similar to FeSe.