High-T_c superconductivity induced by doping rare earth elements into CaFeAsF

TL;DR

Doping rare earth elements into CaFeAsF induces high-temperature superconductivity, with critical temperatures reaching over 50 K, confirmed by resistivity and magnetization measurements, and associated with electron doping evidenced by Hall effect data.

Contribution

This study demonstrates that rare earth doping into CaFeAsF induces high-T_c superconductivity and provides detailed characterization of the structural and electronic changes involved.

Findings

Superconductivity observed at 57.4 K in Nd-doped samples.

Superconductivity observed at 52.8 K in Pr-doped samples.

Hall effect measurements indicate electron doping from rare earth elements.

Abstract

We have successfully synthesized the fluoride-arsenide compounds Ca$_{1-x}$RE$_x$FeAsF (RE=Nd, Pr; x=0, 0.6). The x-ray powder diffraction confirmed that the main phases of our samples are Ca$_{1-x}$RE$_x$FeAsF with the ZrCuSiAs structure. By measuring resistivity, superconductivity was observed at 57.4 K in Nd-doped and 52.8 K in Pr-doped samples with x=0.6. Bulk superconductivity was also proved by the DC magnetization measurements in both samples. Hall effect measurements revealed hole-like charge carriers in the parent compound CaFeAsF with a clear resistivity anomaly below 118 K, while the Hall coefficient $R_H$ in the normal state is negative for the superconducting samples Ca$_{0.4}$Nd$_{0.6}$FeAsF and Ca$_{0.4}$Pr$_{0.6}$FeAsF. This indicates that the rare earth element doping introduces electrons into CaFeAsF which induces the high temperature superconductivity.