Revisiting the electron-doped SmFeAsO: enhanced superconductivity up to 58.6 K by Th and F codoping

TL;DR

This study demonstrates that codoping SmFeAsO with Th and F significantly enhances its superconducting transition temperature up to 58.6K, surpassing previous records in electron-doped 1111-type iron-based superconductors.

Contribution

It introduces a novel Th and F codoping strategy that increases Tc in SmFeAsO beyond existing limits, with detailed synthesis and characterization.

Findings

Maximum Tc of 58.6K achieved with x=0.2, y=0.225

Codoping improves Tc more than single doping

Excess doping introduces impurities and reduces superconductivity

Abstract

In the iron-based high-Tc bulk superconductors, Tc above 50K was only observed in the electron-doped 1111-type compounds. Here we revisit the electron-doped SmFeAsO polycrystals to make a further investigation for the highest T-c in these materials. To introduce more electron carriers and less crystal lattice distortions, we study the Th and F codoping effects into the Sm-O layers with heavy electron doping. Dozens of Sm1-x Th-x FeAsO1-y F-y samples are synthesized through the solid state reaction method, and these samples are carefully characterized by the structural, resistive, and magnetic measurements. We find that the codoping of Th and F clearly enhances the superconducting T-c more than the Th or F single-doped samples, with the highest record T-c up to 58.6K when x= 0.2 and y= 0.225. Further element doping causes more impurities and lattice distortions in the samples with a weakened superconductivity.