电场作用下高分子中自陷束缚激子的极化

用同时计入电场、对称破缺项t_e和电子-晶格相互作用的紧束缚模型研究了电场作用下高分子中的自陷束缚激子.发现电场使高分子中自陷束缚激子内电荷发生转移，出现极化.极化程度随场强增加，也与t_e有关.并发现t_e≤0.1 eV时，双激子态表现出反向极化特性，这一特性可根据极化的量子力学理论得到理解：对高分子的自陷束缚激子，其禁带中央附近存在两个靠得很近的定域电子态即上定域态和下定域态，用微扰论说明了上定域态是反向极化而下定域态为正向极化；双激子态即上     

原子无序起伏对反向极化稳定性的影响

考虑到缺陷、温度效应、掺杂等外界环境的影响,用方形随机分布和高斯随机分布模拟了格点原子的无序起伏,研究了在电场中高分子材料的双激子态反向极化的稳定性,发现当原子涨落不大于0.0148nm时,反向极化能够稳定存在.在格点扰动达到原子间距的14时,反向极化消失.进一步研究了简并参数te与反向极化的关系,同时讨论了在无序起伏较大时正向极化的起因. 关键词： 反向极化 双激子态 原子无序起伏     

高分子中双激子态对外电场的线性响应

在外电场中,非简并基态共轭高分子中的双激子具有反向极化的奇异特性.利用响应函数求得高分子链的双激子态在任意频率下的动态极化率χ(ω),并通过求ω→0极限,给出双激子态的静态极化率χ,证实了χ确实为负值.并与激子态和基态作了比较,分析了分子负极化率的起因.考察了响应函数在低频时的行为,指出激子和双激子的激发浓度增大会导致材料折射率n(ω)向不同方向变化. 关键词：     

链间耦合对极化子非弹性散射性质的影响

基于一维紧束缚的Su-Schreiffer-Heeger模型, 采用非绝热动力学方法, 研究了链间耦合对聚合物中极化子对非弹性散射性质的影响: 激子的产生依赖于链间耦合, 随着耦合强度的增加, 正负极化子对的电子波函数交叠增强, 利于提高激子的产率; 当耦合区域是极化子的宽度时, 正负极化子对波函数的耦合最充分、耦合最强, 电荷跃迁更容易, 激子产率最大. 关键词： 聚合物 极化子 激子     

极化子单激发态的反向极化研究

通过对有机高分子中极化子的单激发态进行研究，发现该态在外电场下呈现反向极化特征，极化规律与双激子态类似.在强电场下，反向极化消失，极化子单激发态解离为一个单极化子和一个双极化子态. 关键词： 极化子态 激子态 反向极化     

电场作用下高分子中自陷束缚激了的极化

用同时计入电场、对称破损项ｔｅ和电子－晶格相互作用的紧束缚模型研究了电场作用下高分子中的自陷束缚激子，发现电场使高分子中自吵缚激子内电荷发生转移，出现极化，极化程度随场强增加，也与ｔｅ有关，并发现ｔｅ≤０．１ｅＶ时，双激子态表现出反向极化特性，这一特性可根据极化的量子力学化理论得到理解：对高分子的自陷束缚激子，其禁带中央附近存在两上靠得很近的定域电子态即上定域态和下定域态，用微扰论说明限上定域态是     

双分子链中非线性多激子态的动力学研究

在超快激光激发下分子聚集体内有多个激子产生.针对具有链间耦合的双分子链系统,应用密度矩阵理论,在偶极-偶极近似和算符算术平均值近似下通过求解量子主方程计算了不同双链构型下的多激子动力学过程.研究发现在光激发作用下的多激子离域在双链分子系统中,在能量表象下形成激子态能带.激子态能带的宽度和激子占据能级随双分子链构型的不同而不同.对于链间和链内均为H型排列的分子链,激子态能带变宽,激子态优先占据在高阶能级上.在不同能级下的激子具有不同的动力学演变特点.若链间耦合较强,激子态通过链间耦合传递,与分子是否直接受到激发没有直接关系,激发态在两个链内的转移周期与最近邻的链间耦合有直接关系.     

与压缩真空库耦合的单模腔内三量子点中激子纠缠

研究了与压缩真空库场耦合的单模腔中三个量子点中激子间纠缠的动力学行为.结果表明：如果不考虑腔模与激子吸收，激子演化为纯的纠缠态.当腔场与一压缩真空库耦合时，激子间形成混合三模高斯纠缠态；在长时极限下，激子态为一稳定的混合三模高斯纠缠态.通过求解激子的特征函数，发现激子态的纯度与纠缠不仅依赖于腔场的初态，并且还与库的双光子关联强度密切相关. 关键词： 纠缠 纯度 压缩真空库 量子点     

基态非简并聚合物中的极化子和双极化子动力学

研究了极化子和双极化子在基态非简并聚合物中的动力学.弱电场下，发现载流子为带电极 化子或双极化子，它们的晶格态与电荷态始终耦合在一起同步运动.极化子比双极化子的运 动速度快，存在饱和速度，且它们的饱和速度随聚合物非简并度的增加而降低；强电场下， 元激发的电荷态将脱离晶格态的束缚而快速运动，参与导电的不再是极化子或双极化子，而 是电子直接导电. 关键词： 极化子 双极化子 动力学模拟     

自旋轨道耦合Su-Schrieffer-Heeger原子链系统的电子输运特性

在Su-Schrieffer-Heeger (SSH)原子链中,电子在胞内和胞间的跳跃依赖于其自旋时,即SSH原子链存在自旋轨道耦合作用时,存在不同缠绕数的非平庸拓扑边缘态.如何探测自旋轨道耦合SSH原子链不同缠绕数的边缘态是一个重要问题.本文在紧束缚近似下研究了自旋轨道耦合SSH原子链的非平庸拓扑边缘态性质及其零能附近的电子输运特性.研究发现四重和二重简并边缘态的缠绕数分别为2和1;并且仅当源极入射电子的自旋被极化(铁磁电极)时,自旋轨道耦合SSH原子链在零能附近的电子输运特性才能反映其边缘态的能谱特性.尤其是,随着自旋轨道耦合SSH原子链与左、右导线之间的耦合强度由弱到强改变,对于缠绕数为2的四重简并边缘态,入射电子在零能附近的透射峰数目将从4个变为0;而对于缠绕数为1的二重简并边缘态情形,其透射峰数目将从2个变为0.因此,在源极为铁磁电极的情形下,通过观察自旋轨道耦合SSH原子链在零能附近电子共振透射峰的数目随着其与左、右导线之间耦合强度的变化,来探测其不同缠绕数的边缘态.上述结果为基于电子输运特性探测自旋轨道耦合SSH原子链不同拓扑性质的边缘态提供了一种可选择的理论方案.     

Effect of interchain coupling on a biexciton in organic polymers

The effect of interchain coupling on the formation and the stability of a biexciton is studied in poly (p-phenylene vinylene) chains in the framework of the tight-binding approach. We obtain an intrachain exciton and biexciton as well as an interchain exciton and biexciton through a double-photon excitation. It is found that a biexciton is energetically favourable to two single excitons even when there exists an interchain coupling. There is a turnover value t_⊥C of the interchain coupling for the formation of a biexciton, beyond which two excitons are combined into one biexciton. The binding energy of a biexciton is calculated to decrease with the increase of interchain coupling, which indicates that a biexciton is relatively stable in polymers with a weak interchain coupling. The conclusion is consistent with the experimental observations. In addition, a suggestion about how to improve the yielding efficiency or the formation of biexcitons in actual applications is given.     

The effect of interchain coupling on the reverse polarization of a high-energy exciton in conjugated polymers

By using the one-dimensional extended Su–Schrieffer–Heeger model, we investigate the effect of interchain coupling on the reverse polarization of a high-energy exciton in conjugated polymers. Our results show that, without interchain coupling, the high-energy exciton is completely localized in one chain, which could be reversely polarized by an electric field. However, when taking into account interchain coupling, the high-energy exciton tends to extend between two chains. Its reverse polarization would be reduced accordingly. We also find that the interchain coupling effect is more obvious for polymers with a stronger non-degenerate confinement. Besides this, the effect of electron–electron interaction is also discussed.     

The influence of the lattice polarization on the biexciton binding energy

The ground state of the biexciton in the lattice polarization field using both Haken and recently derived effective Hamiltonians is studied. The variational wave function possessing the full symmetry of the complex and allowing the analytical evaluation of the energy matrix elements is proposed. The biexciton binding energy is calculated as a function of electron-phonon coupling constant and of phonon energy in the case of equal electron and hole masses.     

高分子中激子和双激子的极化率(解析计算)

高分子的电致发光是载流子在电场中的输运和复合,为了阐明它的机理,需要研究高分子中激子的极化性质,首先求得了激子和双激子的解析解,然后用线性响应的Green函数方法计 算了两者的极化率,解析地证明了一个重要的结论：激子的极化率为正,双激子的极化率为负.从激子跃迁至双激子,高分子的电偶极矩要反转方向. 关键词： 激子 双激子 解析解 负极化率     

Exciton-Boson Formalism in the Theory of Laser-Excited Semiconductors and Its Application in Coherent Four-Wave-Mixing Spectroscopy

By the use of a bosonization transformation and group-theoretical arguments, the Hamiltonian of an electron–hole–photon system in a laser-excited direct two-band semiconductor is transcribed into that of an exciton–photon system with the particle spins rigorously taken into consideration. It is shown that the third-order optical nonlinearities in the spectral region below the band edge have their microscopic origin in two-exciton correlations, which are expressed in terms of the effective exciton–exciton and anharmonic exciton–photon interactions. The dependence of the interparticle interactions on the spin states of quasiparticles is behind the polarization dependence of the semiconductor nonlinear optical response. On the example of the system of heavy hole excitons in quantum wells, grown from compounds with the zinc blende type of symmetry, it is demonstrated that the effective exciton–exciton interaction in two-exciton states with nonzero total spin is repulsive, while in zero-spin states it is attractive, which may result in the biexciton formation. The derived Heisenberg equations of motion for the exciton and biexciton operators form the basis for a theoretical study of the coherent four-wave-mixing in GaAs and ZnSe quantum wells. It is readily apparent from the equations that in different polarization configurations the coherent four-wave-mixing is generated by different ingredients of two-exciton Coulomb correlations: in the co-circular configuration, it is the interexciton repulsion, in the cross-linear configuration, the formation of the biexciton and its coupling to excitons, and in the collinear configuration, both of them jointly. The obtained expressions for the time-resolved and frequency-resolved four-wave-mixing signals adequately describe the main characteristics and various details of wave mixing phenomena, including a biexciton signature in the appropriate polarization configurations. Results of the work clarify the microscopic mechanism of the polarization dependence in coherent four-wave-mixing spectroscopy in semiconductor quantum wells.     

Observation of dressed excitonic states in a single quantum dot

We report the observation of dressed states of a quantum dot. The optically excited exciton and biexciton states of the quantum dot are coupled by a strong laser field and the resulting spectral signatures are measured using differential transmission of a probe field. We demonstrate that the anisotropic electron-hole exchange interaction induced splitting between the x- and y-polarized excitonic states can be completely erased by using the ac-Stark effect induced by the coupling field, without causing any appreciable broadening of the spectral lines. We also show that by varying the polarization and strength of a resonant coupling field, we can effectively change the polarization axis of the quantum dot.     

聚合物中产生双激子的新通道

由于聚合物中的双激子能产生新奇的光致极化反转现象,如何在聚合物中产生双激子变成为一个重要的研究课题.在现在已知的产生双激子的通道以外,提出了一条新的通道:双电子激发,并用动力学方法研究了此通道产生双激子的弛豫过程(包括键结构畸变和电子态的方面),确定了双激子形成和极化反转所需要的时间. 关键词： 聚合物 双激子 通道     

链间耦合对聚乙炔多链体系中电子极化子再激发态的影响

采用拓展紧束缚Su-Schrieffer-Heeger(SSH)模型,研究了链间耦合对反式聚乙炔多链体系中电子极化子再激发态的晶格位形、净电荷密度、局域能级波函数和态密度的影响.结果发现:对于两条链体系,当链间耦合很小(t⊥≤0.01 e V)时,注入到系统中的电子只会在第一条链上诱发产生一个晶格缺陷,形成电子极化子再激发态,这和单链体系是一致,而第二条链仍是二聚化基态.随着链间耦合的增大,第一条链上缺陷的局域度减少而第二条链上的缺陷局域度相应增加,直至两条链上的位形相同;对于多条链(5条链和6条链)体系,当耦合很小(t⊥≤0.05 e V)时,电子极化子再激发态也只会存在于一条链上,当链间耦合较强时,极化子再激发态会在链间层次性地扩展开来,并不会出现多条链位形相同;从两条链的能级图上可以看到随着链间耦合t⊥的增大,体系的带隙不断的增大和电子态密度显示的是完全吻合的,体系的导电性减弱.通过分析两条链体系在t⊥=0 e V和t⊥=0.1 e V的能级态密度,发现链间耦合越强,则中间局域能级的态密度越小,最后没有中间局域态.