Strong electron-electron correlation and weak localization in CeO_{0.9}F_{0.1}Fe_{1-x}Co_xAs

TL;DR

This study investigates how cobalt doping affects superconductivity, electron correlations, and localization in CeO_{0.9}F_{0.1}Fe_{1-x}Co_xAs, revealing complex interactions between layers and electronic properties.

Contribution

It demonstrates the interplay of charge carriers in different layers and the effects of cobalt doping on superconductivity and localization in CeO_{0.9}F_{0.1}FeAs.

Findings

Cobalt doping reduces Tc compared to individual doping.

Resistivity shows T^2 dependence indicating strong electron-electron correlation.

Evidence of weak localization near Tc with negative magnetoresistance.

Abstract

Electron-doping of the semimetal (CeOFeAs) by either fluorine (max Tc ~ 43 K)or cobalt (max Tc ~ 11 K) leads to superconductivity. Here we show the effect of transition metal (Co) substitution at the iron site on the superconducting properties of CeO0.9F0.1FeAs (Tc ~38 K)to understand the interplay of charge carriers in both the rare earth-oxygen and Fe-As layers. Simultaneous doping of equivalent number of charge carriers in both layers leads to a Tc of 9.8 K which is lower than the Tc obtained when either the conducting layer (CeAs) or charge reservoir layer (CeO) is individually doped. This suggests a clear interplay between the two layers to control the superconductivity. The resistivity shows a T2 dependence (T >>Tc) which indicates strong electron-electron correlation. Hall coefficient and thermoelectric power indicate increased carrier concentration with cobalt doping in CeO0.9F0.1FeAs. The rf penetration depth both for CeO0.9F0.1Fe0.95Co0.05As and CeO0.9F0.1FeAs show an exponential temperature dependence with a gap value of ~ 1.6 and 1.9 meV. A resistance minimum is observed in the normal state near Tc which also shows negative magnetoresistance and provides evidence for the onset of weak localization.