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

低维电子晶格系统中光致相变的动力学

基本信息

批准号：
11215201
负责人：
OGAWA Tetsuo
金额：
$ 7.81万
依托单位：
Osaka University Department of Physics (2000-2001)Tohoku University (1999)
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research on Priority Areas (B)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2001
项目状态：
已结题

项目摘要

(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

(1)通过激发态的光致相变理论-光致多米诺过程：利用由局域电子和晶格组成的一维模型，在绝热或绝热近似下，从理论上讨论了通过激发态的光致结构相变。我们表明，光激发仅在一个位点上的整体结构变化是可能的，我们阐明了发生这种现象的条件。本文还从光致成核和畴壁的多米诺骨牌过程的角度详细研究了非平衡一阶相变的时空动力学。在绝热状态下，光子自发发射后，初始局部结构变化(i)保留在局部，（ii）协同诱导全局结构变化，或（iii）消失并返回到初始阶段，这取决于邻近位点之间相互作用的强度。的动态特征，更多的情况下（ii）的特征是确定性多米诺骨牌过程；在强（弱）耗散的情况下，两相之间的畴壁以恒定速度（随速度变化）确定性地运动，而没有进一步的自发辐射。在非绝热状态下，存在类似的三种类型的构造变化。畴壁动力学被描述为随机多米诺骨牌过程，伴随着连续的辐射跃迁。提出了一种新的理论处理方法来研究绝热与绝热的交叉。我们还澄清了对摩擦的依赖（能量耗散率）。在弱摩擦和强相互作用的情况下，发现了新的光致多米诺效应。在这种多米诺骨牌运动中，光激发态仍然处于电子激发态。(2)有限寿命系统的相分离动力学理论：我们研究了有限寿命系统中旋量分解的理论动力学，以阐明超越金兹堡-朗道-威尔逊现象学的粒子间相互作用的影响。这是基于从具有有限寿命的相互作用晶格-气体模型导出的粗粒度哈密顿量。将系统的信息简化为单点分布函数和动力结构因子的闭型耦合积分微分方程。这些方程明确地涉及粒子间相互作用。我们定量地发现，在连续波产生的情况下，有限寿命阻止了相分离和有序的形成。在数值上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：我们用一种新的玻色子化方法推导了描述半导体-光子耦合系统双激子相关的玻色子化哈密顿量，该方法充分考虑了激子偏离理想玻色子的影响。这种偏差效应源于激子是复合粒子，在激子相互重叠的情况下，其特征表现得很明显。我们称这种效应为复合粒子效应（CPE）。本研究导出的哈密顿量包括了以往工作的结果作为CPE的低阶项。在介绍了任意尺寸和电子-空穴质量比的玻色子化方法的一般理论之后，我们还演示了在重空穴极限下光子场耦合的半导体体系中的应用。玻色子哈密顿量表明，CPE使激子-激子散射强度增强，光跃迁幅度发生了质的变化。哈密顿量描述了双激子束缚态和散射态。(4)量子对偶电体中光致合作现象的现象学理论：我们在考虑软模声子偶极子和光掺杂电子偶极子相互作用的横向Ising模型的基础上，从理论上研究了光激发量子对偶电体中电子偶极子诱导相变。根据平均场近似，当电子-偶极子的浓度和声子-偶极子与电子-偶极子之间的相互作用达到适当值时，介电磁化率的温度依赖性表现为从准电到铁电的相变。为了发生相变，这些值分别有下限。我们还研究了介质磁化率与均匀电场的关系。少