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arXiv 0807.0735cond-mat.str-el
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(TMTTF)$_2$ X中电荷有序转变的晶格效应证据

Evidence for Lattice Effects at the Charge-Ordering Transition in (TMTTF)$_2$X

M. de Souza, P. Foury-Leylekian, A. Moradpour, J. -P. Pouget, M. Lang

摘要:

高分辨率的热膨胀测量已被执行探索神秘的“无结构的转变”在(TMTTF)$_{2}$ X(X = PF $_{6}$和AsF $_{6}$),其中在$T_{CO}$的电荷有序与铁电秩序的开始相一致。特别是不同的晶格效应被发现在$T_{CO}$在单轴膨胀沿层间$\textbf{\textit{c*}}$方向。我们提出了一个计划,涉及沿TMTTF堆栈的电荷调制和它的耦合抗衡离子X $^{-}$的位移。这些阴离子的位移,解除反转对称性,使铁电秩序的发展,确定的3D电荷模式没有歧义。在$T_{int}$ $\simeq$ 0.6 $\cdot$ $T_{CO}$下发现了两种材料的另一个异常证据,表明与电荷排序相关的相变。

英文摘要:

High-resolution thermal expansion measurements have been performed for exploring the mysterious "structureless transition" in (TMTTF)$_{2}$X (X = PF$_{6}$ and AsF$_{6}$), where charge ordering at $T_{CO}$ coincides with the onset of ferroelectric order. Particularly distinct lattice effects are found at $T_{CO}$ in the uniaxial expansivity along the interstack $\textbf{\textit{c*}}$-direction. We propose a scheme involving a charge modulation along the TMTTF stacks and its coupling to displacements of the counteranions X$^{-}$. These anion shifts, which lift the inversion symmetry enabling ferroelectric order to develop, determine the 3D charge pattern without ambiguity. Evidence is found for another anomaly for both materials at $T_{int}$ $\simeq$ 0.6 $\cdot$ $T_{CO}$ indicative of a phase transition related to the charge ordering.

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