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Origin of the metal-insulator transition of orbital-ordered spin-singlet system BaVS3

轨道有序自旋单线态BaVS3金属-绝缘体转变的起源

基本信息

批准号：
11440107
负责人：
SHIGA Masayuki
金额：
$ 10.24万
依托单位：
KYOTO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2001
项目状态：
已结题

项目摘要

A triangular-lattice (hexagonal) transition-metal sulfide BaVS3 shows a metal-insulator transition at 70 K. The origin of this transition would be related to spin, charge and orbital degrees of freedom, and/or low-dimensionality of the crystal structure and spin frustration, which has been attracting much attention of many researchers. Therefore the elucidation of the origin is worth investigating. The crystal structure is the hexagonal perovskite type, where vanadium atoms form one-dimensional chains along the c axis and a triangular lattice in the c plane. The formal valence of vanadium is 4+, hence in the state of spin 1/2. The purpose of this project is to grow high-quality crystals of BaVS3 and to make clear the origin of the metalinsulator transition with use of various sophisticated experimental methods. In an early stage, based on experimental results reported in literature and our NMR results, we proposed a model, which is the orbital-ordered spin-singlet state (driven by spin frustration) as appeared in the title of this project. After some experiments, however, we obtained new results which are apparently inconsistent with the model. Thus, unexpectedly, we had to check the reported experimental results step by step. As a result we found many reported data and their analyses insufficient. The conclusion obtained from new experimental results are as follows: BaVSS is a three-dimensional but anisotropic conductor, in which d orbitals form bands both along the c direction and in the c plane. These bands have considerably different characters but both contribute to the metalinsulator transition. In other words, BaVSS is a very unique anisotropic metal, where the interplay between one-dimensional-like and two-dimensional-like interactions gives rise to complicated electronic properties.

过渡金属硫化物BaVS 3在70 K时表现出金属-绝缘体转变。这种转变的起源与自旋、电荷和轨道的自由度有关，也可能与晶体结构的低维性和自旋阻挫有关。因此，其起源的阐明是值得研究的。晶体结构是六方钙钛矿型，其中钒原子形成沿c轴沿着的一维链和在c平面中的三角形晶格。钒的形式价态为4+，因此处于自旋1/2的状态。该项目的目的是生长高质量的BaVS 3晶体，并使用各种复杂的实验方法来明确金属绝缘体转变的起源。在早期阶段，基于文献中报道的实验结果和我们的NMR结果，我们提出了一个模型，这是轨道有序的自旋单重态（由自旋阻挫驱动）出现在这个项目的标题。然而，经过一些实验，我们得到了新的结果，这显然是不一致的模型。因此，出乎意料的是，我们不得不一步一步地检查报告的实验结果。因此，我们发现许多报告的数据和分析不足。新的实验结果表明：BaVSS是一种三维各向异性导体，d轨道在c面内和沿着c方向都形成带.这些带有相当不同的字符，但都有助于金属绝缘体过渡。换句话说，BaVSS是一种非常独特的各向异性金属，其中一维和二维相互作用之间的相互作用产生了复杂的电子性质。