Spin Density and Quantum Fluctuations in Quasi-One-Dimensional Conductors

为了研究低维电子系统中自旋密度的涨落，研究了准一维有机导体中排斥相互作用的作用。对以下三个问题进行了研究。(1)通过计算四分之一填充带Hubbard模型的集体模，研究了公度自旋密度波的涨落。纵模显示了2k_F-SDW和4k_F-CDW的差距和共存。(2)通过将基于玻色化的相位哈密顿量应用于两个具有向后和向前散射的排斥相互作用的耦合链，研究了准一维有机导体中链间跳跃的作用。SDW态与超导态的竞争解释了准一维导体中的相图。(3)本文用从玻色子平均场理论研究了DCNQI-Cu盐中的金属-绝缘体相变，并将其应用于考虑电子-声子相互作用的周期性安德森模型.通过计算M-I-M的重入跃迁、相图比热、磁化率、尺寸效应和反铁磁态，证明了在强关联存在下，M-I跃迁是Peierls跃迁。因此，我们已经显示了M-I转变的机制。

The role of repulsive interaction in quasi-one-dimensional organic conductors has been studied in order to examine the fluctuation of spin density in low-dimensioanl electron system. Following three subjects have been investigated. (1) The fluctuation of the commensurate spin density wave (SDW) has been examined by calculating collective modes of a Hubbard model with a quarter-filled band. The longitudinal mode shows the gap and the coexistence of the 2k_F-SDW and the 4k_F-CDW.The effect of anion lattice was examined in terms of a phase Hamiltonian. (2) A role of interchain hopping in quasi-1D organic conductors was examined by applying the phase Hamiltonian based on the bosonization to two coupled chains with the repulsive interaction of backward and forward scatterings. The competition of SDW state and superconducting state explains the phase diagram of in the quasi-1D conductors. (3) The metal-insulatortarnsition in DCNQI-Cu salts was examined by applying the slave-boson mean-field theory to the periodic Anderson model with the electron-phonon (e-p) interaction. The fact that the M-I transition is the Peierls transition in the presence of the strong correlation has been shown by calculating the reentrant transition of M-I-M,the phase diagram specific heat and magnetic susceptibility, the dimensional effect and the antiferromagnetic state. Thus we have shown the mechanism of the M-I transition.