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

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关联电子系统如Ce单斜晶石和Yb_4As_3所表现出的新现象背后的物理机制。(1)用高压和磁场下的中子和X射线衍射研究了Ce离子的磁有序状态(CeP、CeAs、CeSb)，在Ce离子晶格中周期性地出现了几乎完全极化的Ce离子的铁磁层，Γ_7晶场基态具有较小的磁矩。结果表明，Ce单肽的磁结构对材料和外加压力的依赖关系可以解释为它对载流子密度的依赖。这些发现支持这样一种观点，即Ce单烟碱的奇异性质源于化合物…中固有的p-f混合效应所介导的磁极化子效应。(2)在前人对Yb_4As_3的中子散射研究中，我们发现Yb_4As_3在290K经历电荷有序转变，由电荷有序引起的一维Yb^&lt；3&gt；链表现出一维量子磁性，可以用S=L/2 ID海森伯模型很好地解释。然而，令人费解的是，比热等宏观性质的测量表明在磁场下打开了一个能隙，这与模型不一致。我们在磁场作用下进行了非弹性和极化的中子散射实验，直接观察到了自旋激发谱中能隙的打开。我们还发现，我们的工作中观察到的能隙对磁场的依赖关系与用保角场论处理能隙打开现象的理论相一致，该理论用保角场论来解释由于链中Yb^和Lt；3&Gt；离子对之间的Dzyalosinsky-Moriya相互作用而产生的交错场效应。这些事实表明，Yb_4As_3被认为是研究低维量子磁性的一种新的模型材料，这种低维量子磁性是在稀土材料中首次发现的，尽管很低的载流子在该体系中的作用尚不清楚。较少

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