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。以下三个主题已被调查。(1)通过计算具有四分之一填充带的Hubbard模型的集体模态，研究了相应自旋密度波（SDW）的波动。纵向模态显示2k_F-SDW和4k_F-CDW的间隙和共存。用相哈密顿量考察了阴离子晶格的影响。(2)将基于玻色子化的相哈密顿量应用于具有向后和正向散射排斥相互作用的两个耦合链上，研究了链间跳变在准一维有机导体中的作用。SDW态和超导态的竞争解释了准一维导体的相图。(3)利用电子-声子（e-p）相互作用的周期Anderson模型，应用从色-玻色子平均场理论研究了DCNQI-Cu盐中金属-绝缘体跃迁。通过计算M-I- m的可重入跃迁、相图比热和磁化率、尺寸效应和反铁磁态，证明了M-I跃迁是存在强相关的peerls跃迁。因此，我们已经展示了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.