Photoinduced Phase Transitions and Nonequilibrium Order Formation in Molecular Materials

分子材料中的光致相变和非平衡有序形成

基本信息

批准号：
15540354
负责人：
YONEMITSU Kenji
金额：
$ 2.24万
依托单位：
Institute for Molecular Science (2004-2006)Okazaki National Research Institutes (2003)
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2006
项目状态：
已结题

项目摘要

In mixed-stack charge-transfer DMTTF-QBr_nCl_<4-n> complexes, the neutral-ionic phase transition takes place at zero temperature if the composition n and pressure are tuned. From the pressure dependence of the transition temperature and the paraelectric behavior following the Barrett formula, it is regarded as a quantum phase transition. Quantum paraelectricity generally appears when quantum fluctuations destroy the ordering of local polarizations. In the above materials, local polarizations appear in the ionic phase, but the quantum paraelectricity appears in the neutral phase only. To consider its origin, we represent polarizations in the ionic phase by Sz=+1/-1, a neutral site by Sz=0, and obtain mean-field solutions in the quantum Blume-Emery-Griffiths model. The quantum tunneling term leads to charge-transfer fluctuations, which cause partial ionicity in the neutral phase. As a consequence, the dielectric permittivity follows the Barrett formula in the neutral phase near the quant … More um critical point.In order to study consequences of the differences between the ionic-to-neutral and neutral-to-ionic transitions in the one-dimensional extended Peierls-Hubbard model with alternating potentials for the TTF-CA complex, we introduce a double pulse of oscillating electric field in the time-dependent Schrodinger equation and vary the interval between the two pulses as well as their strengths. When the dimerized ionic phase is photoexcited, the interference effect is clearly observed owing to the coherence of charge density and lattice displacements. The two pulses constructively interfere with each other if the interval is a multiple of the period of the optical lattice vibration, while they destructively interfere if the interval is a half-odd integer times the period, in the processes toward the neutral phase. Meanwhile, when the neutral phase is photoexcited, the interference effect is weakly observed, where the photoinduced lattice oscillations are considerably incoherent due to random phases. Less

在混合堆电荷转移 DMTTF-QBr_nCl_<4-n> 配合物中，如果根据转变温度的压力依赖性和顺电行为调整成分 n 和压力，则中性离子相变会在零温度下发生。根据Barrett公式，量子顺电性一般是在量子涨落破坏局域极化有序性时出现的。在上述材料中，局域极化出现在离子相中，但量子相变。顺电性仅出现在中性相中，为了考虑其起源，我们用 Sz=+1/-1 表示离子相中的极化，用 Sz=0 表示中性位点，并获得量子 Blume-Emery- 中的平均场解。格里菲斯模型。量子隧道项导致电荷转移波动，从而导致中性相中的部分离子性，因此，中性相中的介电常数在量子临界点附近遵循巴雷特公式。为了研究 TTF-CA 复合物具有交替电势的一维扩展 Peierls-Hubbard 模型中离子到中性和中性到离子转变之间差异的后果，我们引入了双脉冲当二聚离子相被光激发时，由于时间相关的薛定谔方程中的振荡电场并改变两个脉冲之间的间隔及其强度，可以清楚地观察到干涉效应。如果间隔是光学晶格振动周期的倍数，则电荷密度和晶格位移的相干性相互相长干涉，而如果间隔是周期的半奇数倍，则它们相消干涉。同时，当中性相被光激发时，观察到微弱的干涉效应，其中由于随机相较少，光致晶格振荡相当不相干。