Photoinduced Phase Transitions and Nonequilibrium Order Formation in Molecular Materials

在混合堆叠电荷转移DMTTF-QBrnCl4-n&gt；络合物中，如果调节组成n和压力，中性-离子相变发生在零温度。从相变温度的压力依赖关系和遵循Barrett公式的顺电行为来看，它被认为是一个量子相变。量子顺电一般出现在量子涨落破坏局域极化的有序性时。在上述材料中，局域极化出现在离子相，而量子顺电只出现在中性相。为了考虑它的起源，我们用Sz=+1/-1来表示离子相的极化，用Sz=0来表示中性位置，并在量子Blume-Emery-Griffiths模型中得到平均场解。量子隧道项导致电荷转移涨落，从而导致中性相中的部分电离性。因此，在量子…附近的中性相中，介电常数遵循巴雷特公式。为了研究TTF-CA络合物的一维扩展Peierls-Hubbard模型中离子到中性和中性到离子跃迁的不同结果，我们在含时薛定谔方程中引入了双脉冲振荡电场，并改变了两个脉冲之间的间隔和强度。当二聚离子相被光激发时，由于电荷密度和晶格位移的相干，明显地观察到了干涉效应。在朝向中性相的过程中，如果间隔是光学晶格振动周期的倍数，则两个脉冲建设性地相互干扰，而如果间隔是该周期的半奇整数倍，则它们破坏性地干涉。同时，当中性相被光激发时，干涉效应很弱，由于随机位相的存在，光致晶格振荡是相当不相干的。较少

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