Effective carrier type and field-dependence of the reduced-Tc superconducting state in SrFe(2-x)Ni(x)As2

TL;DR

This study investigates the superconducting properties of SrFe(2-x)Ni(x)As2, revealing electron doping effects, critical field behaviors, and field-dependent superconductivity in a reduced-Tc iron-pnictide system.

Contribution

It provides detailed measurements of critical fields, doping effects, and field dependence in SrFe(2-x)Ni(x)As2, highlighting its unique superconducting characteristics compared to higher-Tc counterparts.

Findings

Ni doping results in dominant electron-like response.

Critical fields Hc1 and Hc2 are quantified for optimally doped samples.

Hc2(0) exceeds conventional paramagnetic and orbital limits.

Abstract

Measurements of the Hall effect, thermoelectric power, magnetic susceptibility and upper and lower critical fields were performed on single crystals of SrFe(2-x)Ni(x)As2, an FeAs-based superconducting system that exhibits a reduced superconducting transition temperature Tc in comparison to most other iron-pnictide superconductors. Studies of the Hall and thermoelectric responses indicate that Ni substitution in this system results in a dominant electron-like response, consistent with electron doping in other similar systems but with a weaker change in the Hall coefficient and a more gradual change in the thermoelectric response with Ni concentration. For optimally doped samples with full superconducting volume fraction, the lower and upper critical fields were determined to be Hc1(1.8 K)= 0.08T and Hc2(0)= 25T, respectively, with lower-Tc samples showing reduced values and indications of inhomogeneous superconductivity. Comparable to other higher-Tc FeAs-based materials, the temperature dependence of the upper critical field, dHc2/dT, is linear over a wide temperature range, and the large values of Hc2(0) greatly exceed conventional estimates of paramagnetic and orbital limits.