Study of noble electronic phases in the low-carrier strongly correlated systems under extreme conditions by diffraction techniques

利用衍射技术研究极端条件下低载流子强关联体系中的稀有电子相

基本信息

批准号：
10304030
负责人：
KOHGI Masahumi
金额：
$ 25.16万
依托单位：
TOKYO METROPOLITAN UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 2001
项目状态：
已结题

项目摘要

The purpose of the present research is to clarify the physics behind the novel phenomena exhibited by the low-carrier strongly correlated electron systems such as Ce-monopnictides and Yb_4As_3 by neutron scattering and X-ray diffraction. The main results of the project are as follows :(1) We have revealed by neutron and X-ray diffraction under high pressures as well as under magnetic fields that, in the magnetic ordered state of Ce-monopnictide (CeP, CeAs, CeSb), ferromangnetic layers of almost fully polarized Ce ions appear periodically in the lattice of Ce ions with the Γ_7 crystal field ground state with small magnetic moment. It is shown that the dependence of the magnetic structure of Ce-monopnictides on material as well as on applied pressure can be interpreted as its dependence on the carrier density. These findings support the idea that the exotic properties of Ce-monopnictides originate from the magnetic polaron effect mediated by the p-f mixing effect inherent in the compound … More s.(2) In the previous neutron scattering studies on Yb_4As_3, we showed that the material undergoes the charge order transition at 290K, and that the one-dimensional Yb^<3+> chains caused by the charge ordering exhibit one-dimensional quantum magnetism explained well by the S=l/2 ID Heisenberg model. However, it was a puzzle that the measurements of macroscopic properties such as specific heat indicate the opening of an energy gap under magnetic field being inconsistent with the model. We performed the inelastic and polarized neutron scattering experiments under magnetic field and observed directly the opening of the gap in the spin excitation spectrum. It was also found that the magnetic field dependence of the energy gap observed in our work agrees well with the theory which treats the gap opening phenomenon by applying the conformal field theory to the staggered field effect due to the Dzyalosinsky-Moriya interaction between Yb^<3+> ion pairs in the chains. These facts show that Yb_4As_3 is regarded as a new model material to study the low dimensional quantum magnetism which is firstly found among the rare-earth materials although the role of the very low carrier in the system is still unclear. Less

本研究的目的是通过中子散射和X射线衍射来阐明低载流子强相关电子系统（例如Ce-monopnictides和Yb_4As_3）所表现出的新现象背后的物理原理。该项目的主要结果如下。 :(1) 我们通过高压和磁场下的中子和 X 射线衍射揭示，在磁有序状态下，Ce-monopnictide（CeP、CeAs、 CeSb)中，在具有小磁矩的Γ_7晶场基态的Ce离子晶格中周期性地出现几乎完全极化的Ce离子的铁磁性层，这表明Ce单硝化物的磁性结构对材料和磁矩的依赖性。这些发现支持这样的观点：Ce-单硝化物的奇异特性源于 p-f 介导的磁极化子效应。 (2) 在之前对 Yb_4As_3 的中子散射研究中，我们发现该材料在 290K 时经历了电荷级转变，并且由以下因素引起的一维 Yb^<3+> 链电荷排序表现出一维量子磁性，可以用 S=l/2 ID 海森堡模型很好地解释。然而，诸如比热等宏观特性的测量表明磁性下能隙的打开是一个难题。我们在磁场下进行了非弹性和极化中子散射实验，并直接观察到自旋激发光谱中能隙的开口，我们还发现我们的工作中观察到的能隙的磁场依赖性。与通过将共形场理论应用于由于链中 Yb^<3+> 离子对之间的 Dzyalosinsky-Moriya 相互作用而产生的交错场效应来处理间隙打开现象的理论非常吻合。这些事实表明： Yb_4As_3被认为是稀土材料中首次发现的研究低维量子磁性的新模型材料，但极低载流子在体系中的作用尚不清楚。