Metastable domains and potential energy surfaces in organic charge-transfer salts with neutral-ionic phase transitions
Metastable domains and potential energy surfaces in organic charge-transfer salts with neutral-ionic phase transitions
复制标题
具有中性离子相变的有机电荷转移盐中的亚稳域和势能表面
DOI：
10.1103/physrevb.75.155119
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发表时间：
2007
影响因子：
3.7
通讯作者：
A. Painelli
中科院分区：
文献类型：
--
作者：
Z. Soos;A. Painelli
将与晶格声子和分子振动线性耦合的修改后的Hubbard模型应用于有机电荷转移（CT）盐（例如四硫富瓦烯-氯醌（TTF-CA））的结构和电子不稳定性。势能面（PES）的相关模型被发现正是在有限的一维（1D）系统与平均场近似的三维库仑相互作用和参数接近一阶或二阶相变。一阶相变附近的PES具有多个极小值，具有不同的$\ensuremath{\rho}$值，即基态CT的程度。亚稳畴的能量与它们的长度L、过渡处的不连续性Delta和两个畴壁的能量W有关。尖锐和放松的畴壁建模自由无自旋费米子耦合到声子和分子振动，其基态PES是在链中获得高达1000个网站。当$\ensuremath{\Delta}\ensuremath{\rho}$足够小时，亚稳域在低温下变得热可及，其中电子激发的玻尔兹曼布居可以忽略不计。TTF-CA的压力引起的转变进行了讨论，在稳定和亚稳域与不同的$\ensuremath{\rho}$之间的平衡，使用以前的参数的温度引起的转变，其中亚稳域是不可访问的热。在相关或不相关的模型，线性耦合的电子缓慢，谐波坐标晶格和分子振动导致强烈的非谐PES附近的电子或结构不稳定性。CT盐与中性离子过渡说明晶格声子之间的竞争，驱动一个二阶Peierls过渡和分子振动，有利于一阶$\ensuremath{\Delta}\ensuremath{\rho}$。
A modified Hubbard model with linear coupling to both lattice phonons and molecular vibrations is applied to the structural and electronic instabilities of organic charge-transfer (CT) salts such as tetrathiafulvalene-chloranil (TTF-CA). The potential energy surface (PES) of the correlated model is found exactly in finite one-dimensional (1D) systems with a mean-field approximation for 3D Coulomb interactions and parameters close to first or second-order phase transitions. The PES near a first-order transition has multiple minima with different values of $\ensuremath{\rho}$, the degree of CT in the ground state. The energy of metastable domains is related to their length $L$, to the discontinuity $\ensuremath{\Delta}\ensuremath{\rho}$ at the transition, and to the energy $2{E}_{w}$ of two domain walls. Sharp and relaxed domain walls are modeled by free spinless fermions coupled to both phonons and molecular vibrations whose ground-state PES is obtained in chains of up to 1000 sites. When $\ensuremath{\Delta}\ensuremath{\rho}$ is sufficiently small, metastable domains become thermally accessible at low temperature where the Boltzmann population of electronic excitations is negligible. The pressure-induced transition of TTF-CA is discussed in terms of an equilibrium between stable and metastable domains with different $\ensuremath{\rho}$, using previous parameters for the temperature-induced transition, where metastable domains are not accessible thermally. In either correlated or uncorrelated models, linear coupling of electrons to slow, harmonic coordinates for lattice and molecular vibrations leads to strongly anharmonic PES near an electronic or structural instability. CT salts with neutral-ionic transitions illustrate competition between a lattice phonon that drives a second-order Peierls transition and molecular vibrations that favor a first-order $\ensuremath{\Delta}\ensuremath{\rho}$.