High-T _c superconductivity induced by doping rare-earth elements into CaFeAsF

Abstract

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.

Structural collapse and superconductivity in rare-earth-doped CaFe2As2

“…27) 122 compounds which have a maximum T c of ∼ 38 K, and is more comparable to that found in the fluorine-based materials (Ca,R)FeAsF, 28 where similar rare earth electron-doping with Pr and Nd results in T c values approaching the highest reported for any noncuprate material.…”

Superconductivity at Tc = 44 K in LixFe2Se2(NH3)y

“…The highest transition temperatures of Fe based superconductors to date are in the vicinity of 56 K and were reported already within the first year after the initial discovery [3,4]. Meanwhile a variety of families has been identified [5,6,7,8] all of which share a common structural unit, namely Fe 2 As 2 or Fe 2 Se 2 layers which are responsible for carrying superconductivity (see [9] and [10] for recent reviews).…”

Magnetic lattice dynamics of the oxygen-free FeAs pnictides: how sensitive are phonons to magnetic ordering?

“…However, a much higher Tc of 56 K and 57.4 K has been found for Sr 0.5 Sm 0.5 FeAsF [6] and Ca 0. 4 Nd 0.6 FeAsF [7], respectively. The 1111 oxygen based compounds SmFeAsO 0.9 F 0.1 [8] and Gd 0.8 Th 0.2 FeAsO [9] also have high Tc of 55 K and 56 K respectively.…”