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arXiv 1204.0613cond-mat.supr-conphysics.chem-ph
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用扩展X射线吸收精细结构研究超导体K_{0.8} Fe_{1.6} Se_{2}中的大局域无序

Large local disorder in the superconducting K_{0.8}Fe_{1.6}Se_{2} studied by extended x-ray absorption fine structure

Antonella Iadecola, Boby Joseph, Laura Simonelli, Alessandro Puri, Yoshikazu Mizuguchi, Hiroyuki Takeya, Yoshihiko Takano, Naurang Lal Saini

摘要:

用变温极化扩展X射线吸收精细结构(EXAFS)测量了超导硫属化合物K_{0.8} Fe_{1.6} Se_{2}(T_{c} =31.8 K)在Fe和Se K边的局域结构.我们发现,该系统的特点是由一个大的局部无序。的Fe-Se和Fe-Fe的距离被发现是短于通过衍射测量的距离,而相应的均方相对位移显示大的Fe位无序和相对较大的c轴无序。Fe-Se键长的局部力常数(k ~ 5.8 eV/π ^{2})与二元FeSe超导体中发现的相似,然而,与二元FeSe(k ~ 3.5 eV/π ^{2})相比,Fe-Fe键长似乎变得灵活(k ~ 2.1 eV/π ^{2}),这表明K_{0.8} Fe_{1.6} Se_{2}中的Fe-Fe网络部分弛豫。结果表明,标题系统的玻璃态性质,与超导电性类似的颗粒材料。

英文摘要:

We have measured local structure of superconducting K_{0.8}Fe_{1.6}Se_{2} chalcogenide (T_{c}=31.8 K) by temperature dependent polarized extended x-ray absorption fine structure (EXAFS) at the Fe and Se K-edges. We find that the system is characterized by a large local disorder. The Fe-Se and Fe-Fe distances are found to be shorter than the distances measured by diffraction, while the corresponding mean square relative displacements reveal large Fe-site disorder and relatively large c-axis disorder. The local force constant for Fe-Se bondlength (k ~ 5.8 eV/Å^{2}) is similar to the one found in the binary FeSe superconductor, however, the Fe-Fe bondlength appears to get flexible (k ~ 2.1 eV/Å^{2}) in comparison to the binary FeSe (k ~ 3.5 eV/Å^{2}), an indication of partly relaxed Fe-Fe networks in K_{0.8}Fe_{1.6}Se_{2}. The results suggest glassy nature of the title system, with the superconductivity being similar to the one in the granular materials.

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