Effects of simultaneous carrier doping in the charge reservoir and conducting layers of superconducting CeO 0.9F 0.1Fe 1−xCo xAs

Abstract

Electron-doping of the semimetal (CeOFeAs) by either fluorine (max T c ∼ 43 K) or cobalt (max T c ∼ 11 K) leads to superconductivity. Here we show the effect of transition metal (Co) substitution at the iron site on the superconducting properties of CeO 0.9F 0.1FeAs ( T c ∼ 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 T c of 9.8 K which is lower than the T c obtained when either the conducting layer (FeAs) or charge reservoir layer (CeO) is individually doped. This suggests a clear interplay between the two layers to control the superconductivity. Resistivity upturn and negative magnetoresistance are observed with Co doping that is interpreted in the gamut of Kondo effect. Hall coefficient and thermoelectric power indicate increased carrier concentration with cobalt doping in CeO 0.9F 0.1FeAs. The rf penetration depth both for CeO 0.9F 0.1Fe 0.95Co 0.05As and CeO 0.9F 0.1FeAs show an exponential temperature dependence with gap values of ∼1.6 and 1.9 meV respectively.