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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.

磁学最重要的问题之一是建立一个既适用于局域磁矩又适用于巡回电子磁学的统一理论。提出了以d为空间维度的1/d展开法。这既适用于局域磁矩，也适用于巡回电子磁学。在最佳单位近似(SSA)中可以正确地考虑局域量子自旋涨落。SSA等价于求解映射的Anderson模型，使其从映射条件中自相容地确定。这意味着近藤效应不仅在稀磁合金中起着重要的作用，而且在周期性强关联电子系统中也起着重要的作用。场间效应可以从SSA开始微扰处理，用1/d展开法研究了各种问题。(1)研究了正弦结构和螺旋结构之间磁结构的相互作用。(2)除了模-模耦合机制外，居里-魏斯定律的巡游电子磁性还有另一种机制：磁平均场的温度依赖性，在L/d中是领先的。(3)提出了铜氧化物超导体的高温超导机制：附近重准粒子之间形成dx&lt；x2-y2&gt；波库珀对，Mott相变。配对相互作用主要是近邻之间的超交换相互作用。(4)研究了一种新型的磁交换相互作用。它是由自旋通道中准粒子对激子的虚交换引起的。这种交换相互作用的强度大约是准半圆环的带宽。(5)认为CeU_2Si_2的超磁相变主要是由这种交换作用引起的。