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Theoretical study on magnetism and superconductivity in almost lo-calized strongly correlated elecron systems

近局域强关联电子系统磁性和超导性的理论研究

基本信息

批准号：
08640434
负责人：
OHKAWA Fusayoshi
金额：
$ 1.47万
依托单位：
HOKKAIDO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1998
项目状态：
已结题

项目摘要

One of the most important issues for magnetism is to construct a unified theory that is applicable to both local-moment magnetism and itinerant electron magnetism. The 1/d expansion methof has been developed, with d being the spatial dimensionality. This is apllicable to both local-moment magnetism and itinerant electron magnetism. Local quantuam spin fluctuations can be correctly considered in the best single-site approximation (SSA). The SSA is equivalent to solving a mapped Anderson model to be self-consistently determined form a maaping condition. This means that the Kondo effect plays a significant and essential role in not only dilute magnetic alloys but also periodical strongly correlated electron systems. Intersite effects can be perturbatively treated starting from the SSA.Various issues have been studied by the 1/d expansion method. (1) The corssover of magnetic structures between sinusoidal and helical stuructures has been studied. (2) There is another mechanism of the Curie-Weiss law for itinerant electron magnetism besides the mode-mode coupling mechanism, which is of higher in 1/d : the temperature dependence of the magnetic mean field, which is of leading order in l/d. (3) A mechanism of high-temperature superconductivity in cuprate-oxide superconductors has been proposed ; the formation of dx_<x2-y2> wave Cooper pairs between heavy quasiparticles in the vicinity, of the Mott transtion. The main pairing interaction is the superexchange interaction between nearest neighbors. (4) A new type of magnetic exchange interaction has been studied. It is caused by the virtual exchange of pair excitatiolns of quasiparticles in spin channels, has been studied. The strength of this exchange interaction is about the bandwidth of quisipartgicles. (5) It has been proposed that a metamagnetic transition in CeRu_2Si_2 is mainly caused by this exchange interaction.

建立一个既适用于局域磁矩磁性又适用于巡游电子磁性的统一理论是磁学研究的重要课题之一。提出了1/d展开法，d为空间维数。这对局域磁矩磁性和巡游电子磁性都是适用的。局域量子自旋涨落可以在最佳单格点近似下正确地考虑。SSA等价于求解一个映射安德森模型，该模型由映射条件自洽确定。这意味着近藤效应不仅在稀磁合金中，而且在周期性强关联电子系统中都起着重要的作用。从SSA出发，可以对场地间的影响进行微扰处理，用1/d展开法对各种问题进行了研究。(1)研究了正弦结构和螺旋结构磁结构的交叉。(2)巡游电子磁性的Curie-Weiss定律除了模-模耦合机制外，还有另一种机制，即平均磁场的温度依赖性，它在1/d中具有较高的阶数。(3)本文提出了铜氧化物超导体高温超导的一种机制：<x2-y2>莫特转变附近重准粒子间dx波库珀对的形成。主要的配对相互作用是最近邻之间的超交换相互作用。(4)本文研究了一种新型的磁交换作用。研究了自旋通道中准粒子对激发态的虚交换引起的自旋通道的自旋极化。这种交换相互作用的强度与准粒子的带宽有关。(5)CeRu_2Si_2的变磁转变主要是由这种交换作用引起的。