The pattern of charge ordering in quasi-one-dimensional organic charge transfer solids
The pattern of charge ordering in quasi-one-dimensional organic charge transfer solids
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准一维有机电荷转移固体中的电荷有序模式
DOI：
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发表时间：
2001
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通讯作者：
D. K. Campbell
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作者：
R. T. Clay;S. Mazumdar;D. K. Campbell
我们批判性地研究了最近提出的两种不同的名义上 1/4 填充有机电荷转移固体 (CTS) 中的电荷排序模型。在一维中，这两个模型的特征分别是 ...1010... 和 ...1100... 形式的位点电荷密度。我们建立了以下理论结果：1）存在临界最近邻库仑相互作用（V_c>2|t|），只有在该相互作用之上，...1010...状态才变为基态； 2）Hartree-Fock平均场理论对V_c的预测不正确； 3）精确的量子蒙特卡罗计算表明V_c随着U的减小而增大； 4) 对于足够强的 e-ph 相互作用，...1010... 态可以经历自旋 Peierls (SP) 跃迁； 5) 对于 V<V_c，在存在 e-ph 相互作用的情况下，...1100...CO 态是基态，并且也会经历 SP 跃迁。我们表明，实验观察清楚地表明 1:2 阴离子 CTS 和 (TMTSF)_2X 类材料中的 ...1100...CO，而具有较窄单电子带宽的 (TMTTF)_2X 的结果更加模糊。在二维方面，我们关注 theta-(BEDT-TTF)_2X 材料，并确定那里的 CO 图案对应于所谓的水平条纹结构，其中 ...1100...CO 沿着电子跳跃较大的两个方向。我们对金属-绝缘体转变时在 theta-(BEDT-TTF)_2X c 方向上观察到的自发键畸变给出了精确的解释，并表明在较低温度下自旋间隙的出现是一种真正的二维效应，不同于通常的 SP 转变。电荷转移固体中的超导性似乎仅限于在绝缘相中表现出...1100...CO 的材料类别。
We examine critically two different recently proposed models of charge ordering in the nominally 1/4-filled organic charge transfer solids (CTS). In one dimension, the two models are characterized by site charge densities of the form ...1010... and ...1100..., respectively. We establish the following theoretical results: 1) there exists a critical nearest-neighbor Coulomb interaction (V_c>2|t|) only above which does the ...1010... state become the ground state; 2) Hartree-Fock mean field theory predicts V_c incorrectly; 3) accurate quantum Monte Carlo calculations indicate that V_c increases with decreasing U; 4) for sufficiently strong e-ph interactions, the ...1010... state can undergo a spin-Peierls (SP) transition; 5) for V<V_c, in the presence of e-ph interactions, the ...1100... CO state is the ground state and also undergoes a SP transition. We show that experimental observations clearly indicate the ...1100... CO in the 1:2 anionic CTS and the (TMTSF)_2X class of materials, while the results for (TMTTF)_2X with narrower one-electron bandwidths are more ambiguous. In two dimensions, we focus on the theta-(BEDT-TTF)_2X materials, and establish that the CO pattern there corresponds to the so-called horizontal stripe structure, with ...1100... CO along the two directions with larger electron hopping. We give precise explanations of the observed spontaneous bond distortions in the c-direction of theta-(BEDT-TTF)_2X at the metal-insulator transition and also show that the appearance of the spin gap at lower temperatures is a true two-dimensional effect different from the usual SP transition. Superconductivity in the charge transfer solids appears to be limited to the class of materials which exhibits the ...1100... CO in the insulating phase.