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.

在重电子系统中，被称为近藤温度的特征能级很小，因此可以人为地控制反铁磁相和超导相之间的相变。理解这种类型的量子临界行为是当前凝聚态物理研究的一个主题。这项研究的主要目的是阐明轨道简并在量子相变中的作用。在本研究中，我们使用了 j-j 耦合方案，因为电子-电子相互作用的重要影响可以通过微扰理论系统地处理。本研究取得的主要成果可概括如下：(1)基于j-j耦合方案，我们为Ce115体系开发了一种有效的哈密顿量，并阐明了其磁性和超导性质。通过电子能带结构计算研究了新发现的超导体PuCoGa_5的电子态。(2)报道了过渡金属化合物LiV_2O_4的重电子行为。为了了解重质量的起源，考虑了轨道简并性，在烧绿石晶格上考虑了扩展的哈伯德型模型。阐明了模型自旋、轨道和自旋-轨道组合涨落模式的性质。(3)针对UGe_2超导现象的起源,研究了模型中两个均匀铁磁相之间发生一级相变的可能性。为 UGe_2 构建。事实证明，由于轨道简并的影响，这种类型的转变是可能的。