Systematic Study of Electronic Structures for Ternary Skutterudite Compounds

三元方钴矿化合物电子结构的系统研究

基本信息

批准号：
12640329
负责人：
TAKEGAHARA Katsuhiko
金额：
$ 2.37万
依托单位：
Hirosaki University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2002
项目状态：
已结题

项目摘要

Systematic study of electronic structures for binary skutterudite compounds (T'X_3 : T' = Co, Rh, Ir and X = P, As, Sb and NiP_3) and ternary skutterudite compounds (RT_4X_<12> : R = rare earth, T = Fe, Ru, Os and X = P, As, Sb) are performed.The electronic band structures are calculated for T'X_3 and La-based ternary compounds by using an FLAPW method. Except for NiP_3, binary compounds are basically semiconductors. La-based ternary compounds are the metal with one hole per formula unit. The main Fermi surface is a distorted cube and the volume is almost a half of the BCC BZ, indicating that the nesting with q=(1,0,0) is likely in ternary skutterudite compounds.PrRu_4P_<12> shows a metal-insulator transition and PrFe_4P_<12> undergoes a non-magnetic ordering. In fact, structural phase transitions are observed in these compounds. The coupling of Fe/Ru ion displacements to the 4f^2 ground state doublet results in a unique symmetry-lowering structural phase transition accompanied by anti-quadrupolar ordering. The instability of the Fermi surface should be coupled, through Fe/Ru displacements, with anti-quadrupolar ordering at the structural phase transitions.Very recently, a new class of heavy fermion superconductivity has been reported in PrOs_4Sb_<12>. The dHvA measurements have been performed for LaOs_4Sb_<12> and PrOs_4Sb_<12>, then it has been revealed they have very similar topology. The Fermi surface of the LDA calculation for PrOs_4Sb_<12> does not explain the experimental dHvA measurement. The LAD + U calculation (f localized case) for PrOs_4Sb_<12> strongly suggest the 4f^2 electrons are localized.The local point symmetry of the rare earth site is T_h. For about two decades, it has been believed that the same formula of crystal electric fields is applicable for all cubic point groups. We find that the new term is non-vanishing for the cubic point groups T_h and T due to the lack of Umklappung and fourfold symmetry axis of the point group O_h.

系统研究二元方钴矿化合物（T'X_3：T' = Co、Rh、Ir 和 X = P、As、Sb 和 NiP_3）和三元方钴矿化合物（RT_4X_<12>：R = 稀土，T = Fe、Ru、Os 和 X = P、As、Sb) 进行计算。使用公式计算了 T'X_3 和 La 基三元化合物的电子能带结构FLAPW方法。除NiP_3外，二元化合物基本上都是半导体。 La基三元化合物是每个式单元具有一个孔的金属。主费米面是一个扭曲的立方体，体积几乎是BCC BZ的一半，表明三元方钴矿化合物中可能存在q=(1,0,0)的嵌套。PrRu_4P_<12>显示出金属绝缘体转变和 PrFe_4P_<12> 经历非磁性排序。事实上，在这些化合物中观察到结构相变。 Fe/Ru 离子位移与 4f^2 基态双峰的耦合导致了独特的降低对称性的结构相变，并伴有反四极有序。费米表面的不稳定性应该通过Fe/Ru位移与结构相变时的反四极有序耦合起来。最近，在PrOs_4Sb_<12>中报道了一类新的重费米子超导性。对 LaOs_4Sb_<12> 和 PrOs_4Sb_<12> 进行了 dHvA 测量，结果表明它们具有非常相似的拓扑结构。 PrOs_4Sb_<12> 的 LDA 计算的费米面不能解释实验 dHvA 测量。 PrOs_4Sb_<12> 的 LAD + U 计算（f 局域情况）强烈表明 4f^2 电子是局域的。稀土位点的局域点对称性为 T_h。大约二十年来，人们一直相信相同的晶体电场公式适用于所有立方点群。我们发现，由于点群 O_h 缺乏 Umklappung 和四重对称轴，因此对于三次点群 T_h 和 T，新项是非消失的。