Doping effects of Co, Ni, and Cu in FeTe0.65Se0.35 single crystals

TL;DR

This study investigates how doping FeTe0.65Se0.35 single crystals with Co, Ni, and Cu affects their superconducting properties, revealing valence-dependent suppression and complex local effects.

Contribution

It provides detailed experimental insights into how different transition metal dopants influence superconductivity and related parameters in FeTe0.65Se0.35.

Findings

Superconductivity is suppressed at rates correlating with impurity valence.

Doping affects critical magnetic fields and coherence length.

Evidence suggests two-component superconducting behavior due to local charge effects.

Abstract

The resistivity, magnetoresistance, and magnetic susceptibility are measured in single crystals of FeTe0.65Se0.35 with Cu, Ni, and Co substitutions for Fe. The crystals are grown by Bridgman's method. The resistivity measurements show that superconductivity disappears with the rate which correlates with the nominal valence of the impurity. From magnetoresistance we evaluate doping effect on the basic superconducting parameters, such as upper critical field and coherence length. We find indications that doping leads to two component superconducting behavior, possibly because of local charge depression around impurities.