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

National Laboratory for Superconductivity, Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences - P. O. Box 603, Beijing 100190, PRC

Corresponding author: hhwen@aphy.iphy.ac.cn

Received: 10 December 2008
Accepted: 23 February 2009

Abstract

We have successfully synthesized the fluoride-arsenide compounds CaRE_xFeAsF (RE = Nd, Pr; x = 0,0.6). The X-ray powder diffraction confirmed that the main phases of our samples are CaRE_xFeAsF with the ZrCuSiAs structure. By measuring resistivity, superconductivity was observed at 56 K in Nd-doped and 52 K in Pr-doped samples with . 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_0.4Nd_0.6FeAsF and Ca_0.4Pr_0.6FeAsF. This indicates that the rare-earth element doping introduces electrons into CaFeAsF, which induces high-temperature superconductivity.