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射线衍射阐明低载流子强相关电子系统（如Ce-monopnictides和Yb_4As_3）所表现出的新现象背后的物理原理。本课题的主要成果如下：(1)在高压和磁场作用下，通过中子和x射线衍射揭示了在磁性有序态（CeP, CeAs, CeSb）中，具有小磁矩的Γ_7晶体场基态的Ce离子晶格中周期性地出现几乎完全极化的Ce离子铁磁层。结果表明，ce -单核苷酸的磁性结构对材料和施加压力的依赖性可以解释为对载流子密度的依赖性。这些发现支持了ce -单nictides的奇异性质源于化合物中固有的p-f混合效应所中介的磁极化子效应的观点。More s.(2)在先前对Yb_4As_3的中子散射研究中，我们发现材料在290K时发生了电荷序跃迁。由电荷排序引起的一维Yb^<3+>链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，令人困惑的是，比热等宏观性质的测量表明，磁场下能量缺口的打开与模型不一致。我们在磁场下进行了非弹性和极化中子散射实验，直接观察了自旋激发谱中间隙的打开。我们还发现，我们所观察到的能隙的磁场依赖性与将共形场理论应用于链中Yb^<3+>离子对之间的Dzyalosinsky-Moriya相互作用引起的交错场效应来处理能隙打开现象的理论是一致的。这些事实表明，尽管极低载流子在体系中的作用尚不清楚，但Yb_4As_3被认为是研究稀土材料中首次发现的低维量子磁性的新模型材料。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