Effect of orbital degeneracy on the heavy electron systems

轨道简并对重电子系统的影响

基本信息

批准号：
14540325
负责人：
UEDA Kazuo
金额：
$ 2.5万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2005
项目状态：
已结题

项目摘要

In the heavy electron systems, a characteristic energy scale called a Kondo temperature is small and thus it is possible to controll artificially phase transition between an antiferromagnetic phase and a superconductive phase. Understanding of this type of quantum critical behaviors is a main theme of the current research of condensed matter physics. The main objective of this study was to clarify the role of orbital degeneracy concerning the quantum phase transition. For this study we used a j-j coupling scheme, since the important effect of electron-electron interaction may be treated by a perturbation theory in a systematic way. The main results obtained through the present study may be summarized as follows :(1) We have developed an effective Hamiltonian for the Ce115 system based on the j-j coupling scheme and clarified its magnetic as well as superconductive properties. Electronic states of PuCoGa_5, which is a newly found superconductor, are studied by electronic band structure calculations.(2) Heavy electron behaviors are reported for LiV_2O_4 which is a transition metal compound. To understand the origin of the heavy mass, an extended Hubbard type model was considered on the pyrochlore lattice taking account of the orbital degeneracy. Nature of spin, orbital, and spin-orbital combined fluctuation modes of the model are clarified.(3) Concerned with the origin of the superconductivity observed in UGe_2, possibility of the first order phase transition between two uniform ferromagnetic phases was investigated for a model constructed for UGe_2. It has turned out that this type of transition is possible due to the effect of orbital degeneracy.

在重型电子系统中，称为近藤温度的特征能量表很小，因此可以控制抗铁磁相和超导相之间的人为相变。了解这种类型的量子关键行为是当前对凝结物理学研究的研究的主要主题。这项研究的主要目的是阐明有关量子相变的轨道变性的作用。在这项研究中，我们使用了J-J耦合方案，因为可以通过系统的方式通过扰动理论来治疗电子电子相互作用的重要效果。通过本研究获得的主要结果可以总结如下：（1）我们基于J-J耦合方案为CE115系统开发了有效的哈密顿量，并阐明了其磁性以及超导性能。 Pucoga_5的电子状态是一种新发现的超导体，通过电子带结构计算研究。（2）据报道，LIV_2O_4的重型电子行为是一种过渡金属化合物。为了了解重物的起源，考虑到轨道变性，在pyrochlore晶格上考虑了扩展的哈伯德型模型。阐明了模型的自旋，轨道和自旋轨道合并的波动模式的性质。（3）与UGE_2中观察到的超导性的起源有关，研究了两个均匀的铁磁相之间的一阶相变的可能性，用于用于UGE_2构建的模型。事实证明，由于轨道变性的影响，这种类型的过渡是可能的。