Theoretical research on orbital orders and fluctuations

从以下几个方面进行了理论研究。*轨道有序相互作用的微观研究我们解释了稀土六硼化物有序模式中特征波数的起源。我们在所谓的LDA+U方法中开发了一种新的计算方案，以便推导出存在轨道有序时的能带结构。结果阐明了能带结构与物理性质之间的关系。*轨道自由度和磁序理论(1)CeB6：在CeB6的四极有序相中，我们预测磁场会诱发交错八极子。在这个项目中，对这些现象的自然解释是在分析Ce离子之间相互作用的基础上提供的。此外，我们还指出了伪偶极相互作用对于理解CeB6中最近邻矩的正交排列的重要性。(2) Yb4As3：该化合物的电荷有序性使其在低温下具有特有的磁性。我们得到了系统的有效哈密顿量，它准确地描述了系统的各向异性，包括Dzyaloshinski-Moriya相互作用。(3) TmTe：该化合物具有立方对称性，具有晶体-电场基态。因此，我们研究了四极序和磁场诱导磁矩的特性，并与CeB6进行了比较。

Theoretical study was made on the following aspects.*Microscopic study of interactions for orbital orderWe explained the origin of characteristic wave numbers in the ordering pattern of rare-earth hexaborides.*Band theory taking account of the orbital orderWe developed a new calculational scheme within the so-called LDA+U method in order to derive the band structure in the presence of orbital orders. The results clarify the relashionship between the band structure and the physical properties.*Theory of orbital degrees of freedom and magnetic order(1) CeB6 : In the quadrupole ordered phase of CeB6, we have predicted that magnetic field induces staggered octupoles. Within this project natural explanation for the phenomena was provided on the basis of analyzing interaction among Ce ions. Furthermore, we pointed out the importance of pseudo-dipolar interactions in understanding the orthogonal arrangement of nearest-neighbor moments in CeB6.(2) Yb4As3 : Charge ordering of this compound leads to a characteristic magnetic property at low temperature. We derived the effective Hamiltonian for the system, which describes accurately the anisotropy including the Dzyaloshinski-Moriya interaction.(3) TmTe : This compound has the cubic symmetry and has the crystalline-electric-field ground state. Hence we examined the character of the quadrupole order and magnetic moment induced by magnetic field, in comparsion with CeB6.