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arXiv · 1602.04266

Evidence for Defect-induced Superconductivity up to 49 K in (Ca1-xRx)Fe2As2

L. Z. Deng·B. Lv·K. Zhao·F. Y. Wei·Y. Y. Xue·Z. Wu·C. W. Chu
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Abstract

To explore the origin of the unusual non-bulk superconductivity with a Tc up to 49 K reported in the rare-earth-doped CaFe2As2 , the chemical composition, magnetization, specific heat, resistivity, and annealing effect are systematically investigated on nominal (Ca1-xRx)Fe2As2 single crystals with different x's and R = La, Ce, Pr, and Nd. All display a doping-independent Tc once superconductivity is induced, a doping-dependent low field superconducting volume fraction f, and a large magnetic anisotropy {\eta} in the superconducting state, suggesting a rather inhomogeneous superconducting state in an otherwise microscale-homogenous superconductor. The wavelength dispersive spectroscopy and specific heat show the presence of defects which are closely related to f, regardless of the R involved. The magnetism further reveals that the defects are mainly superparamagnetic clusters for R = Ce, Pr, and Nd with strong intercluster interactions, implying that defects are locally self-organized. Annealing at 500 {\deg}C, without varying the doping level x, suppresses f profoundly but not the Tc. The above observations provide evidence for the crucial role of defects in the occurrence of the unusually high Tc ~ 49 K in (Ca1-xRx)Fe2As2 and are consistent with the interface-enhanced superconductivity recently proposed.

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L. Z. Deng, B. Lv, K. Zhao, F. Y. Wei, Y. Y. Xue, Z. Wu, C. W. Chu. 2016-02-12. Evidence for Defect-induced Superconductivity up to 49 K in (Ca1-xRx)Fe2As2. https://doi.org/10.1103/physrevb.93.054513

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