Theory of photoinduced phase transitions in itinerant electron systems
Theory of photoinduced phase transitions in itinerant electron systems
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DOI：
10.1016/j.physrep.2008.04.008
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发表时间：
2008-08
期刊：
影响因子：
--
通讯作者：
K. Yonemitsu;K. Nasu
中科院分区：
文献类型：
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作者：
K. Yonemitsu;K. Nasu
本文综述了光致相变的理论研究进展，并结合相关实验进行了评述。在简单介绍了统计系统中的随机演化和定域电子系统中的多米诺效应之后，我们讨论了巡游电子系统中的光致动力学。在模型中需要相关的相互作用来描述光激发后的快速和超快电荷晶格耦合动力学。首先，我们讨论了混合堆电荷转移复合物TTF-CA中的中性离子跃迁。当由链内电荷转移光激发诱导时，离子-中性跃迁的动力学特征为阈值行为，而中性-离子跃迁的动力学特征为近似线性行为。这种差异源于中性相和离子相的电子关联不同。其次，我们处理卤素桥金属配合物，显示金属，莫特绝缘体，电荷密度波，和电荷极化阶段。后两相具有不同的对称性破缺。电荷密度波到电荷极化的跃迁比反向跃迁容易得多。这是澄清考虑微观电荷转移过程。从电荷密度波到Mott绝缘体相和从Mott绝缘体到金属相的转变比低对称相之间的转变快得多。接下来，我们讨论了超快，逆自旋佩尔斯跃迁的有机自由基晶体和碱TCNQ的内部二聚体和二聚体间的电荷转移激发的观点。然后，我们研究了量子顺电钙钛矿SrTiO 3中的光生电子，假设它们与软非谐声子和呼吸型高能声子耦合不同。不同的电子-声子耦合导致两种类型的极化子，一种是具有准全局宇称破坏的“超顺电大极化子”，另一种是仅具有局部宇称破坏的“偏心型自陷极化子”。前者相当于一个带电导电的铁电畴，大大提高了准静态磁化率和电导率。最后，我们概述了时间分辨X射线衍射实验的发展，它直接访问光激发材料中的电子，原子和分子运动的动力学。当三维结构长程有序建立并改变对称性时，它们非常有用。
Theoretical progress in the research of photoinduced phase transitions is reviewed with closely related experiments. After a brief introduction of stochastic evolution in statistical systems and domino effects in localized electron systems, we treat photoinduced dynamics in itinerant-electron systems. Relevant interactions are required in the models to describe the fast and ultrafast charge-lattice-coupled dynamics after photoexcitations. First, we discuss neutral-ionic transitions in the mixed-stack charge-transfer complex, TTF-CA. When induced by intrachain charge-transfer photoexcitations, the dynamics of the ionic-to-neutral transition are characterized by a threshold behavior, while those of the neutral-to-ionic transition by an almost linear behavior. The difference originates from the different electron correlations in the neutral and ionic phases. Second, we deal with halogen-bridged metal complexes, which show metal, Mott insulator, charge-density-wave, and charge–polarization phases. The latter two phases have different broken symmetries. The charge-density-wave to charge–polarization transition is much more easily achieved than the reverse transition. This is clarified by considering microscopic charge-transfer processes. The transition from the charge-density-wave to Mott insulator phases and that from the Mott insulator to metal phases proceed much faster than those between the low-symmetry phases. Next, we discuss ultrafast, inverse spin-Peierls transitions in an organic radical crystal and alkali-TCNQ from the viewpoint of intradimer and interdimer charge-transfer excitations. Then, we study photogenerated electrons in the quantum paraelectric perovskite, SrTiO3, which are assumed to couple differently with soft-anharmonic phonons and breathing-type high-energy phonons. The different electron–phonon couplings result in two types of polarons, a “super-paraelectric large polaron” with a quasi-global parity violation, and an “off-center-type self-trapped polaron” with only a local parity violation. The former is equivalent to a charged and conductive ferroelectric domain, which greatly enhances both the quasi-static electric susceptibility and the electric conductivity. Finally, we outline the development of time-resolved X-ray diffraction experiments, which directly accesses the dynamics of electronic, atomic and molecular motions in photoexcited materials. They are extremely useful when a three-dimensional structural long-range order is established and changes the symmetry.