Antiferromagnetic Order and Superconductivity in Sr4(Mg0.5-xTi0.5+x)2O6Fe2As2 with Electron Doping: 75As-NMR Study

TL;DR

This study uses 75As-NMR to investigate how electron doping in Sr4(Mg0.5-xTi0.5+x)2O6Fe2As2 induces a transition from antiferromagnetic order to superconductivity, revealing structural factors influencing Tc.

Contribution

It demonstrates that electron doping via Ti substitution in thick-layer Fe-based superconductors induces a transition from AFM order to SC, with optimized FeAs4 tetrahedron structure enhancing Tc.

Findings

AFM order present at x=0

Superconductivity emerges at x=0.2 with Tc=36 K

Structural optimization correlates with higher Tc

Abstract

We report an 75As-NMR study on iron (Fe)-based superconductors with thick perovskitetype blocking layers Sr4(Mg0.5-xTi0.5+x)2O6Fe2As2 with x=0 and 0.2. We have found that antiferromagnetic (AFM) order takes place when x=0, and superconductivity (SC) emerges below Tc=36 K when x=0.2. These results reveal that the Fe-pnictides with thick perovskitetype blocks also undergo an evolution from the AFM order to the SC by doping electron carriers into FeAs planes through the chemical substitution of Ti+4 ions for Mg+2 ions, analogous to the F-substitution in LaFeAsO compound. The reason why the Tc=36 K when x=0.2 being higher than the optimally electron-doped LaFeAsO with Tc=27 K relates to the fact that the local tetrahedron structure of FeAs4 is optimized for the onset of SC.