Peierls and spin-Peierls phase transitions in systems with coupled softening modes
Peierls and spin-Peierls phase transitions in systems with coupled softening modes
复制标题
耦合软化模式系统中的 Peierls 和自旋 Peierls 相变
DOI：
10.1103/physrevb.28.2659
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发表时间：
1983
影响因子：
3.7
通讯作者：
Y. Lépine
中科院分区：
文献类型：
--
作者：
Y. Lépine
本文研究了准一维系统中的Peierls和spin-Peierls型相变，其中晶格畸变由多个简正模描述。选择一个模型来描述这种情况下的两个耦合的正常模式。也包括内在结构不稳定的可能性。本文对三维晶格作了平均场处理，得到了两个简正模之间的耦合强度r与下列结果的关系：（1）对应于每一简正模的畸变发生在同一温度，即转变温度是唯一的;最后，（3）对于负的耦合能（Γ< 0），存在Γ的一个值Γ c，使得当Γ< Γ c时跃迁为一级跃迁，当Γ> Γ c时跃迁为二级跃迁。该模型适用于碱金属四氰基醌二甲胺盐。据发现，定性地，阳离子的大小和相变的顺序的转变温度的依赖关系可以充分理解本模型。
Peierls and spin-Peierls-type phase transitions are studied in quasi-one-dimensional systems where the distortion of the lattice is described by more than one normal mode. A model is chosen to describe this situation in the case of two coupled normal modes. A possibility of intrinsic structural instability is also included. A mean-field treatment is effected for a three-dimensional lattice and the following results have been obtained as a function of Γ, the strength of the coupling between the two normal modes:(1) The distortions corresponding to each normal mode occur at the same temperature, ie, the transition temperature is unique;(2) the transition temperature increases when Γ decreases; finally,(3) for negative coupling energies (Γ< 0) there exists a value Γ c, of Γ, such that for Γ< Γ c the transition is of first order and for Γ> Γ c the transition is of second order. This model is applied to the alkali-metal tetracyanoquinodimethanide salts. It is found that, qualitatively, the dependence of the transition temperature on cation size and the order of the phase transition can be adequately understood in terms of the present model.