Thorium-doping induced superconductivity up to 56 K in Gd1-xThxFeAsO

TL;DR

This paper reports the discovery of superconductivity up to 56 K in Gd1-xThxFeAsO achieved by Th4+ doping, which relaxes lattice mismatch and enhances Tc beyond previous records in iron-based arsenides.

Contribution

It introduces Th4+ doping in GdFeAsO as a novel method to induce high-temperature superconductivity, surpassing previous Tc limits in similar compounds.

Findings

Superconductivity observed at Tc up to 56 K in Gd1-xThxFeAsO.

Th4+ doping relaxes lattice mismatch, enabling higher Tc.

Th doping is effective in inducing high-temperature superconductivity.

Abstract

Following the discovery of superconductivity in an iron-based arsenide LaO1-xFxFeAs with a superconducting transition temperature (Tc) of 26 K[1], Tc was pushed up surprisingly to above 40 K by either applying pressure[2] or replacing La with Sm[3], Ce[4], Nd[5] and Pr[6]. The maximum Tc has climbed to 55 K, observed in SmO1-xFxFeAs[7, 8] and SmFeAsO1-x[9]. The value of Tc was found to increase with decreasing lattice parameters in LnFeAsO1-xFx (Ln stands for the lanthanide elements) at an apparently optimal doping level. However, the F- doping in GdFeAsO is particularly difficult[10,11] due to the lattice mismatch between the Gd2O2 layers and Fe2As2 layers. Here we report observation of superconductivity with Tc as high as 56 K by the Th4+ substitution for Gd3+ in GdFeAsO. The incorporation of relatively large Th4+ ions relaxes the lattice mismatch, hence induces the high temperature superconductivity.