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Search for a novel double honeycomb lattice superconductor

寻找新型双蜂窝晶格超导体

基本信息

批准号：
13640347
负责人：
SHAMOTO Shin-ichi
金额：
$ 2.3万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13640347/
关键词：
Double honeycomb lattice Superconducting Material search HfNCl 超電導超伝道

项目摘要

We have synthesized double honeycomb lattice superconductors, such as Li_xZrNCl (T_c=15 K), Li_xNBr (T_c=13 K), and Na_xHfNCl (T_c=20-23 K) under ambient pressure. By synthesizing large amount of sample, we have succeeded to determine these structural parameters by Rietveld analysis using neutron powder diffraction data one by one. As a result, we found the close relationship between the transfer integral estimated by Harrison approximation and the superconducting transition temperature T_c in these compounds. This is partially because Na_xHfNCl has large Debye temperature in spite of the large mass of a Hf atom, I.e., stiff lattice. It basically suggests that the longer bond distance between the nearest neighbor transition metal atoms are, the higher T_c is. Based on this finding, we have selected YOCl, TaON, and CeSI as high-T_c candidates of double honeycomb lattice superconductors. Our simple estimation predicts that Na_xYOCl would have a T_c of 30 K. After we successfully sysnthesized Li_xYOCl powder sample in DRI-LAB glove box under an atmosphere of less than 1 ppm moisture, we found it was an insulator with curious temperature dependence of magnetization. This is the first discovery of a double honeycomb lattice insulator. It proves that Na_xHfNCl locates close to an insulator region in our transfer integral phase diagram. This result suggests that Li_xYOCl sample might be a high-T_c superconductor under pressure.

我们在常压下合成了Li_xZrNCl（T_c=15 K）、Li_xNBr（T_c=13 K）和Na_xHfNCl（T_c=20-23 K）等双蜂窝晶格超导体。通过合成大量的样品，我们成功地利用中子粉末衍射数据，通过Rietveld分析，逐一确定了这些结构参数。结果表明，在这些化合物中，用Harrison近似估算的转移积分与超导转变温度T_c有密切的关系。这部分是因为Na_xHfNCl具有大的德拜温度，尽管Hf原子的质量很大，刚性晶格这基本上表明，最近邻过渡金属原子间的键距越大，T_c越高。基于这一发现，我们选择了YOCl，TaON和CeSI作为高T_c双蜂窝晶格超导体的候选者。我们简单地估计了Na_xYOCl的T_c为30 K.在DRI-LAB手套箱中，在小于1 ppm的湿度下成功地合成了Li_xYOCl粉末样品，发现它是一种具有奇怪的磁化强度温度依赖性的绝缘体。这是首次发现的双层蜂窝格子绝缘子。证明了Na_xHfNCl在传输积分相图中位于绝缘体附近。这一结果表明Li_xYOCl样品在压力下可能是一种高温超导体。