Superconductivity in SrFe_(2-x)Co_xAs_2: Internal Doping of the Iron Arsenide Layers

TL;DR

This study reports superconductivity up to 20 K in SrFe_(2-x)Co_xAs_2, demonstrating bulk superconductivity despite disorder, and suggests an itinerant electron mechanism based on structural, magnetic, and computational analyses.

Contribution

It provides new insights into electron doping effects in iron arsenide superconductors and challenges the cuprate-like pairing scenarios.

Findings

Superconductivity observed for 0.2 < x < 0.4 with T_c up to 20 K.

Bulk superconductivity confirmed through thermodynamic measurements.

Co substitution suppresses magnetic order via band structure shifts.

Abstract

In the electron doped compounds SrFe_(2-x)Co_xAs_2 superconductivity with T_c up to 20 K is observed for 0.2 < x < 0.4. Results of structure determination, magnetic susceptibility, electrical resistivity, and specific heat are reported. The observation of bulk superconductivity in all thermodynamic properties -- despite strong disorder in the Fe-As layer -- favors an itinerant picture in contrast to the cuprates and renders a p- or d-wave scenario unlikely. DFT calculations find that the substitution of Fe by Co (x > 0.3) leads to the suppression of the magnetic ordering present in SrFe_2As_2 due to a rigid down-shift of the Fe-3d_(x^2-y^2) related band edge in the density of states.