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arXiv 0705.2349cond-mat.str-el
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电子-晶格耦合对θ-(ET)2X中电荷序的影响

Effects of Electron-Lattice Coupling on Charge Order in θ-(ET)2X

Yasuhiro Tanaka, Kenji Yonemitsu

摘要:

在Hartree-Fock近似下,采用扩展的具有Peierls型电子-晶格耦合的哈伯德模型,研究了准二维有机导体θ-(ET)2X(ET=BEDT-TTF)中伴随晶格畸变的电荷有序.结果表明,θ-(ET)_2RbZn(SCN)_4晶体的水平条纹电荷有序态是由自洽确定的晶格畸变稳定的.此外,在最近邻库仑相互作用Vij的各向异性的存在下,水平电荷顺序变得比任何其他电荷模式,如对角,垂直和3倍型状态更稳定。在有限的温度下,我们比较了各种电荷有序状态的自由能,并发现一个一阶过渡从金属态与3倍电荷顺序的绝缘状态与水平电荷顺序。讨论了格点自由度在实现水平电荷序中的作用及其与θ-(ET)2X实验的关系。

英文摘要:

Charge ordering accompanied by lattice distortion in quasi-two dimensional organic conductors θ-(ET)2X (ET=BEDT-TTF) is studied by using an extended Hubbard model with Peierls-type electron-lattice couplings within the Hartree-Fock approximation. It is found that the horizontal-stripe charge-ordered state, which is experimentally observed in θ-(ET)2RbZn(SCN)4, is stabilized by the self-consistently determined lattice distortion. Furthermore, in the presence of the anisotropy in nearest-neighbor Coulomb interactions Vij, the horizontal charge order becomes more stable than any other charge patterns such as diagonal, vertical and 3-fold-type states. At finite temperatures, we compare the free energies of various charge-ordered states and find a first-order transition from a metallic state with 3-fold charge order to the insulating state with the horizontal charge order. The role of lattice degrees of freedom in the realization of the horizontal charge order and the relevance to experiments on θ-(ET)2X are discussed.

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