Upper critical field, superconducting energy gaps, and Seebeck coefficient in La0.8Th0.2OFeAs

TL;DR

This study synthesizes a new La0.8Th0.2OFeAs superconductor with a Tc of 30.3 K, revealing insights into its lattice, critical field, electron doping, and superconducting gap properties.

Contribution

It introduces a novel electron-doped La-oxypnictide superconductor with the highest Tc among La-based oxypnictides synthesized at ambient pressure.

Findings

Superconducting transition temperature of 30.3 K.

Upper critical field Hc2(0) of 47 T.

Evidence for a nodeless superconducting gap of 1.4 meV.

Abstract

We report the synthesis and characterization of a new electron-doped La-oxypnictide superconductor by partial substitution of lanthanum by thorium. The superconducting transition temperature at about 30.3 K was observed in La0.8Th0.2OFeAs which is the highest in La-based oxypnictide superconductors synthesized at ambient pressure. We find that the decrease in lattice parameters with Th doping in LaOFeAs is more drastic as compared to that obtained by high pressure (6 GPa) synthesis of oxygen deficient LaOFeAs. The resistivity and magnetic susceptibility measurements yield an upper critical field Hc2 (0) of 47 T. Partial substitution of Th in place of La induces electron doping as evidenced by negative Seebeck coefficient. The temperature dependent magnetic penetration depth data provides strong evidence for a nodeless low energy gap of 1.4 meV.