Theoretical Study of Nested Spin Fluctuations

通过这个为期三年的项目，证明了在费米液体理论的基础上，考虑嵌套自旋涨落的影响，可以统一地理解高t_c铜酸盐的自旋间隙行为和自旋电荷分离方面的异常性质。也就是说，这种异常行为的起源已被证明是由于准粒子的费米表面在接近反铁磁莫特绝缘状态时不可避免地嵌套，因此在低能状态下相干自旋波动的谱权减小。同时，指出自旋涨落的非相干部分也起着至关重要的作用，以便一致地理解这些异常行为。研究还表明，V_2O_3的异常行为，被认为是Mott跃迁的典型例子，可以理解为是由嵌套自旋涨落引起的。在合理参数值的d-p模型的Gutzwiller处理的基础上，证明了高t_c铜酸盐是属于中间耦合区的材料，其Mott跃迁的起源应归因于伴随费米表面嵌套的反铁磁相关。用Luttinger-Ward的骨架展开法对流动-局域二象性模型进行了微观论证，该模型为强相关金属的嵌套自旋波动理论提供了基础。URu_2Si_2弱磁性的异常性质可以理解为U离子f^2组态单线态基态的矩致机制以及部分费米表面的嵌套效应。特别地，可以很自然地推导出，T_N，尼尔温度，m (0)， T=0时的有序矩对磁场的依赖关系是由明显不同的磁场大小来缩放的。少

Through this three years project, it has been shown that the anomalous properties of high-T_c cuprates, such as spin-gap behaviors and spin-charge separation aspects, can be understood in a unified way by taking into account the effects of nested spin-fluctuations on the basis of the Fermi liquid theory. Namely, the origin of such anomalous behaviors has been shown to be attributed to the fact that the spectral weight of coherent spin fluctuations decreases in the low-energy regime because the Fermi surface of the quasiparticles is inevitably nested as the antiferromagnetic Mott insulating state is approached. At the same time, it has been pointed out that the incoherent part of spin fluctuations also plays a crucial role in order to understand these anomalous behaviors consistently.It was also shown that the anomalous behaviors of V_2O_3, which had been considered to be a typical example exhibiting the Mott transition, can be understood as those originating from the nested spin-fluctu … More ations.It was shown, on the basis of the Gutzwiller treatment of d-p model with reasonable values of parameters, that the high-T_c cuprates are the materials belonging to the intermediate coupling regime and their origin of Mott transition should be attributed to the antiferromagnetic correlations accompanied by the nesting of the Fermi surface.A microsopic justification of the Itinerant-Localized Duality Model, which had been offering the basis of a theory of nested spin-fluctuations in strongly correlated metals, was given by means of the skeleton-expansion method of Luttinger-Ward.The anomalous properties of weak magnetism of URu_2Si_2 was shown to be understood as a moment-induced mechanism of the crystal-field singlet ground state of f^2-configuration of U ion together with the nesting effect of a part of the Fermi surface. In particular, it was derived naturally that the magnetic-field dependence of T_N, the Neel temperature, and m (0), the ordered moment at T=0, are scaled by apparently different magnitudes of magnetic field. Less