We have successfully synthesized the fluoride-arsenide compounds Ca1−xRExFeAsF (RE=Nd, Pr; x=0, 0.6). The x-ray powder diffraction confirmed that the main phases of our samples are Ca1−xRExFeAsF 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 RH in the normal state is negative for the superconducting samples Ca0.4Nd0.6FeAsF and Ca0.4Pr0.6FeAsF. This indicates that the rare earth element doping introduces electrons into CaFeAsF which induces the high temperature superconductivity.
@article{arxiv.0812.1192,
title = {High-T_c superconductivity induced by doping rare earth elements into CaFeAsF},
author = {Peng Cheng and Bing Shen and Gang Mu and Xiyu Zhu and Fei Han and Bin Zeng and Hai-Hu Wen},
journal= {arXiv preprint arXiv:0812.1192},
year = {2009}
}