Search of tow-dimensional metallic state in a transition metal sulfide BaVS3 showing a metal-insulator transition

在BaVS 3中，自旋为1/2的钒原子形成一维链，其也形成三角形晶格。尽管结构简单，但其物理性质相当复杂，因为许多自由度，如轨道简并和电荷不稳定性与结构一维性和自旋阻挫等竞争。BaVS 3物理进展相当缓慢的原因是无法获得高质量的单晶。然而，几年前碲助熔剂法的发展，使研究进入了一个新的阶段。本研究的主要目的是在兵库大学研究生院材料科学研究科建立新的设备来生长BaVS 3单晶，这是我们最近的努力所实现的。在BaVS 3中，有两个具有不同特征的3d能带（轨道），这两个能带都参与了金属-绝缘体转变。在目前的研究中，我们注意到不同的敏感性的波段对e ...更多信息 外部场我们预计，负责一维电导率的dx 2型带和强关联的dx型带的灵敏度是不同的，从而导致当金属态被场破坏时形成中间态。在早期的状态中，我们称之为“二维金属态”。目的之一是通过实验检测状态。本课题是与东京大学ISSP的Narumi和Kindo合作研究的。研究结果已在最近发表的一篇论文中进行了总结。结果发现，“二维金属态”的符号是不合适的，而应该被称为“三维金属态与导电性差”。在发表的论文中，我们称之为“不良导体”。我们对BaVS 3的研究是通过在相对较低的频率范围内观察低温绝缘状态的多个核磁共振信号而开始的。虽然我们将它们解释为NQR（即没有内场），但我们随后的中子衍射实验确定基态是反铁磁的，因此核共振对应于有限的内场。这一结果提出了新的问题：（1）为什么内场非常小？(2)为什么磁场是分开的。我们现在推测BaVS 3的金属-绝缘体转变是从金属到某种金属簇的转变。由于磁性金属簇没有系统的NMR研究，因此，我们选择了具有GaMo 4S 8型结构的过渡金属硫化物，其中过渡金属四面体簇被注入，并系统地研究了它们的NMR，以与典型的金属和绝缘体进行比较。少

In BaVS3, vanadium atoms with spin 1/2 form one-dimensional chains, which also form a triangular lattice. In spite of the simple structure, its physical properties are quite complicated, because a number of degrees of freedom such as orbital degeneracies and charge instability compete with structural one-dimensionality and spin frustration etc. The reason why the physics of BaVS3 progresses quite slowly was the unavailability of single crystals with good quality. Several yeas ago, however, the tellurium flux method was developed, leading the investigation to a new stage. The primary purpose of the present study is to set up new facilities to grow BaVS3 single crystals at Graduate School of Material Science, University of Hyogo, which was fulfilled by our recent efforts.In BaVS3, there are two 3d bands (orbitals) with different characteristics, both of which participate in the metal-insulator transition. In the present study, we noted the different sensitivity of the bands against the e … More xternal field. We expected that the sensitivity of the dx2-type band responsible for the one-dimensional conductivity and the strongly correlated dxy-type band is different, resulting in the formation of an intermediate state when the metallic state is destroyed by the field. In an early state, we called the state "a two-dimensional metallic state". The one of the purposes was to detect the state experimentally. This subject has been studied as a collaboration work with Narumi and Kindo at ISSP, University of Tokyo. The results have been summarized in a recently published paper. It was found that the notation of "the two-dimensional metallic state" is not appropriate, but should be called a "three-dimensional metallic state with poor conductivity". In the published paper, we call it "a poor conductor".Our study of BaVS3 was initiated by the observation of multiple nuclear magnetic resonance signals in a relatively low frequency range for the low-temperature insulating state. Although we interpreted them as NQR (namely no internal field), our following neutron diffraction experiments established that the ground state is antiferromagnetic, and therefore the nuclear resonances correspond to finite internal fields. This result posed new questions : (1) Why are the internal fields anomalously small? (2) Why are the magnetic sites separated. We now speculate that the metal-insulator transition of BaVS3 is a transition from a metal to a certain kind of metal cluster. Since there has been no systematic NMR investigation on magnetic metal clusters, we have therefore selected transition-metal sulfides with the GaMo4S8 type structure, in which transition-metal tetrahedral clusters are implanted, and investigated their NMR systematically to compare with that of typical metals and insulators. Less