Dynamics of Photoinduced Phase Transitions in Low-Dimensional Electron-Lattice Systems

(1)激发态光致相变理论--光致多米诺过程：在绝热或非绝热近似下，利用由局域电子和晶格组成的一维模型，从理论上讨论了激发态光致结构相变。我们表明，全球结构变化的光激发只有在一个网站是可能的，我们澄清这种现象的发生条件。非平衡一级相变的时空动力学也研究了详细的光致成核和多米诺骨牌过程的域边界（域壁）。在绝热状态下，在光子的自发发射之后，初始局部结构变化（i）保持在局部，（ii）协同地诱导全局结构变化，或（iii）消失并返回到初始相位，这取决于相邻位点之间的相互作用的强度。动力学特征 关于我们 情况（ii）的特征在于确定性多米诺过程;在强（弱）耗散的情况下，两相之间的畴壁以恒定速度（具有变化的速度）确定性地移动，而没有进一步的自发发射。在非绝热区，存在类似的三种结构变化。畴壁动力学被描述为随机多米诺骨牌过程，这是伴随着连续的辐射跃迁。一个新的理论处理也提出了研究之间的绝热和非绝热制度的交叉。我们还澄清摩擦（能量耗散率）的依赖。在弱摩擦和强相互作用的情况下，我们发现了新的光诱导多米诺过程。在这种多米诺骨牌运动中，光激发位点仍然处于激发电子态。(2)有限寿命系统中的相分离动力学理论：我们从理论上研究有限寿命系统中的旋节分解动力学，以澄清金兹伯格-朗道-威尔逊现象学之外的粒子间相互作用的影响。这是基于粗粒度的哈密顿量来自相互作用的晶格气体模型与有限的寿命。系统的信息被简化为封闭形式的耦合积分微分方程的单点分布函数和动力学结构因子。这些方程明确地包含了粒子间的相互作用。我们定量地发现，有限的寿命阻止了连续波产生情况下的相分离和有序形成。数值计算证实了寿命与渐近特征波数之间的普遍关系。(3)多激子系统的玻色子理论：我们采用一种新的玻色子化方法，充分考虑了激子偏离理想玻色子的影响，导出了一个描述双激子耦合系统的玻色子化哈密顿量。这种偏离效应源于激子是复合粒子，在激子相互重叠的情况下，复合粒子的特征表现得更加明显。我们称这种效应为复合粒子效应（CPE）。在这项研究中导出的哈密顿量包括以前的作品作为CPE的低阶项的结果。在介绍了玻色化方法的一般理论和任意维和电子空穴质量比的玻色化方法之后，我们还演示了在重空穴极限下与光子场耦合的半导体体系统的应用。玻色化的哈密顿量表明，CPE引起激子-激子散射强度的增强和光跃迁振幅的质的变化。它也表明，哈密顿量描述两个激子的束缚态和散射态。(4)量子顺电体中光致合作现象的唯象理论：在考虑软模声子偶极与光掺杂电子偶极相互作用的横向伊辛模型的基础上，从理论上研究了光激发量子顺电体中电子偶极诱导的相变。根据平均场近似，温度依赖性的介电常数表现出顺电铁电相变时，电子偶极子的浓度和声子偶极子和电子偶极子之间的相互作用采取适当的值。这些值分别具有下限，以便发生相变。我们还研究了均匀电场的介电常数的依赖关系。少

(1) THEORY OF PHOTOlNDUCED PHASE TRANSITIONS VIA EXCITED STATES - PHOTOINDUCED DOMINO PROCESS : Photoinduced structural phase transitions via excited electronic states are discussed theoretically using a one-dimensional model composed of localized electrons and lattices under the adiabatic or diabatic approximation. We show that the global structural change by photoexcitation only at a site is possible, and we clarify conditions for the occurrence of such phenomena. Spatiotemporal dynamics of nonequilibrium first-order phase transitions is also investigated in detail in terms of photoinduced nucleation and domino processes of the domain boundaries (domain walls). In the adiabatic regime, after the spontaneous emission of a photon, an initial local structural change (i) remains locally, (ii) induces cooperatively a global structural change, or (iii) disappears and returns to the initial phase, depending on the strength of the interaction between neighboring sites. Dynamical features of … More the case (ii) are characterized by the deterministic domino process ; domain walls between the two phases move deterministically at a constant velocity (with changing speed) without further spontaneous emissions in the case of strong (weak) dissipation. In the diabatic regime, similar three types of structural change exist. The domain-wall dynamics is described as the stochastic domino process, which is accompanied by the successive radiative transitions. A new theoretical treatment is also proposed to study crossover between the adiabatic and diabatic regimes. We also clarify dependence on the friction (energy dissipation rate). We find novel photoinduced domino process in the case of weak friction and strong intersite interaction. In this domino motion the photoexcited site is still in an excited electronic state.(2) THEORY OF PHASE-SEPARATION DYNAMICS IN FINITE-LIFETIME SYSTEMS : We study theoretically dynamics of the spinodal decomposition in finite-lifetime systems to clarify effects of the interparticle interactions beyond the Ginzburg-Landau-Wilson phenomenology. This is based on the coarse-grained Hamiltonian derived from the interacting lattice-gas model with a finite lifetime. The information of the system is reduced to closed-form coupled integrodifferential equations for the single-point distribution function and the dynamical structure factor. These equations involve explicitly the interparticle interactions. We find quantitatively that the finite lifetime prevents the phase separation and the order formation in the cw creation case. A universal relation between the lifetime and the asymptotic characteristic wavenumber is confirmed numerically.(3) BOSON THEORY OF MANY-EXCITON SYSTEMS : We derive a bosonized Hamiltonian describing two-exciton correlation of semiconductor-photon coupled systems with a new bosonization method, which takes into full account an effect of deviation of the excitons from ideal bosons. This deviation effect stems from that the excitons are composite particles, whose character appears clearly in the case where the excitons overlap with each other. We call this effect a composite-particle effect (CPE). The Hamiltonian derived in this study includes the results of the previous works as low-order terms of the CPE. After introduction of general theory, of the bosonization method for arbitrary dimension and electron-hole mass ratio, we demonstrate also application to a semiconductor bulk system coupled with a photon field in the heavy-hole limit. The bosonized Hamiltonian shows that the CPE brings about enhancement of exciton-exciton scattering strength and qualitative change of photo-transition amplitude. It is also shown that the Hamiltonian describes two-exciton bound and scattering states.(4) PHENOMENOLOGICAL THEORY OF PHOTOINDUCED COOPERATIVE PHENOMENA IN QUANTUM PARAELECTRICS : We theoretically study an electron-dipole induced phase transition in photoexcited quantum paraelectrics on the basis of the transverse Ising model taking account of the interaction between a soft-mode phonon-dipole and a photodoped electron-dipole. In accordance with the mean-field approximation, temperature-dependence of dielectric susceptibilities exhibits paraelectric to ferroelectric phase transitions when the concentration of the electron-dipole and the interaction between a phonon-dipole and an electron-dipole take appropriate values. These values separately have lower limits in order to occur phase transitions. We also investigate dependence of dielectric susceptibilities on a uniform electric field. Less