Unconventional low dimensional fluctuation in organic conductors

为了研究相关和涨落在低维有机导体中的作用，我们从理论上研究了以下基于玻色子化的系统。(i)在贝加德盐的正常状态下，从绝缘体到金属的转变发生在压力下，贝加德盐表现出电荷间隙。这种跃迁是由电荷间隙与链间跳跃的比值决定的。利用带半填充带的双耦合链，用重整化群方法处理一维波动，研究了其机理。结果表明，当电荷间隙大于链间跳跃时，约束发生。进一步研究了来自相称态的电子填充效应。(2)有机导体的自旋密度波在临界温度的1/3处出现了新的转变。利用双耦合链的相哈密顿量，利用传递积分法研究了链间相位差的影响。结果表明，可通约性能量和链间耦合之间的竞争导致了从相称态到不相称态的过渡。(3)研究了杂质对双耦合无自旋链的影响，以了解链间跳变在准一维体系中的作用。发现当杂质的钉住能大于相互作用引起的链间间隙时，会发生一维局域化。除上述结果外，我们还研究了一维电子的电子态、自旋密度波的集体模式以及杂质对自旋Peirls系统的影响。

We have studied theoretically the following system based on the bosonization in order to study a role of correlation and fluctuation in low dimensional organic conductors. (i) The transition from insulator to metal occurs under pressures in the normal state of Bechgaard salts, which exhibit the charge gap. Such a transition is determined by a ratio of the charge gap to the interchain hopping. The mechanism has been studied by use of two-coupled chains with a half-filled band, in which the one-dimensional fluctuation is treated in terms of the renormalization group method. It is demonstrated that the confinement occurs when the charge gap becomes larger than than the interchain hopping. Further the effect of the electron-filling from the commensurate state has been examined. (2) The spin density wave of organic conductors exhibits a novel transition at temperature of the 1/3 of the critical temperature. By using a phase Hamiltonian for two-coupled chains of SDW, the effect of the phase difference between chain has been investigated by use of the transfer integral method. It is shown that the competition between the commensurability energy and interchain coupling gives rise to the transition from the commensurate state to the incommensurate state. (3) The effect of impurity in two-coupled spinless chain has been studied to understand the role of interchain hopping in quasi-one-dimensional systems. It is found that the one-dimensional localization occurs when the pinning energy of impurity becomes larger than the interaction induced interchain gap. Besides the above results, we have examined the electronic state of one-dimensional electrons, collective modes of spin density wave and the impurity effect on spin Peirls system.