有机共轭高聚物的分子链间耦合局域态

有机共轭高分子中,孤子、极化子及激子都是基本的元激发,对解释有机聚合材料的导电发光特性起着主导作用.孤子、极化子以及激子等在晶格位形上都是各具特征的空间局域状态.本文将讨论在有机共轭高分子中存在着另一种局域态——链间耦合局域态,这种局域态是由于分子链间的相互作用所导致,在相互作用分子链端附近形成势阱,可有效束缚电子和空穴等带电粒子.     

单离子各向异性影响下的一维铁磁链中的孤子

利用行波解法，研究了考虑交换各向异性和单离子各向异性的一维铁磁链，得出椭圆函数波解和孤子解,并讨论了单离子各向异性对椭圆函数波和孤子的影响.研究表明：单离子各向异性对一维铁磁链中椭圆函数波和孤子的激发及其稳定性有显著影响.单离子各向异性不利于易轴铁磁链中椭圆函数波和孤子解的激发，但有利于它们的稳定；而在易平面铁磁链中，单离子各向异性使椭圆函数波和孤子激发变得容易，但不利于它们的稳定.此外，还讨论了单离子各向异性对一维各向同性铁磁链中的孤子激发具有的影响. 关键词： 各向异性 单离子各向异性 孤子 铁磁链     

具有反铁磁相互作用的双铁磁链中的非线性激发

采用双子格模型和相干态表示,研究了链与链之间存在反铁磁相互作用的双铁磁链系统中的非线性激发的性质,得到了孤子的宽度,能量及有效质量。结果表明在不同情况下的各向异性双铁磁链中可以激发拓扑性孤子或非拓性孤子或非拓生反孤子。     

反铁磁链的自旋Peierls相变

通过费米-玻色变换将一维自旋1/2反铁磁链映射为连续玻色场形式,讨论了模型基态能量和激发态能量,证明了此系统存在自旋Peierls相变.并给出了模型基态能量密度与晶格畸变大小的关系.数值计算的结果验证了上述理论的正确性. 关键词：     

一维更键Heisenberg铁磁链间隙非线性元激发

对于一维更键铁磁链Heisenberg模型，在一级近似下：1）存在磁间隙孤子（振动频率位于磁频谱间隙内）和响应扭结（振动频率位于磁频谱内）；2）内禀局域模（振动频率位于所有磁频谱带上方）是不可能存在的． 关键词：     

磁场诱导的单离子各向异性反铁磁链的比热

利用改进的Schwinger玻色子平均场理论,研究了横向外加磁场下自旋为1的单粒子各向异性海森堡反铁磁链的热力学性质.发现在外加磁场下预示这一体系中存在Luttinger液体相—完全极化相相变的比热奇性,并给出了相应的相图.研究还发现,单粒子各向异性对比热的影响较小,这和纵向场的结果完全不同.以上结果对整自旋的反铁磁链具有普适性,对实验研究具有指导性. 关键词： 反铁磁链 热力学性质 Schwinger 玻色子     

Aharonov—Bohm磁通对一维铁磁链中孤子的影响

分析了Ａｈａｒｏｎｏｖ－Ｂｏｈｍ磁通对一维铁磁链中孤子的影响，结果表明Ａｈａｒｏｎｏｖ－Ｂｏｈｍ磁通对孤子的峰值、宽度、静止能量及有效质量均有影响。     

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

从拓展紧束缚模型出发,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（eV）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（0.05eV）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eV和eV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。     

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.     

一维铁磁链中量子孤波的能级和磁矩

使用Hartree近似和一种简化的准离散多标度方法,研究了具有交换作用和经典磁矩相互作用的一维铁磁链中的量子孤波解. 这种一维铁磁链中不仅存在着运动的量子孤波,也存在着静态的量子孤波(即量子内禀局域模).利用所获得的量子孤波解,进一步研究了量子孤波的能级和由量子孤波所携带的磁矩. 研究表明,量子孤波的能量和磁矩都是量子化的,这些结果为正确理解磁性材料中像磁滞回线的量子台阶等宏观量子特性提供了一条可能的途径.     

二维链间扩展的极化子动力学研究

基于扩展的SSH模型,研究了有序耦合聚合物链系统中的极化子动力学,包括极化子的形成过程及其在外场下的输运.发现,当聚合物链间的耦合较强时,注入到系统中的电子会诱发二维链间扩展的极化子态,分布在多条聚合物链上.另外,动力学模拟表明,与一维链内定域极化子相比,在相同的电场强度下二维极化子具有更大的运动速度,这与实验结果一致. 关键词： 链间扩展极化子 链间耦合     

The effect of dimerization on the magnetoresistance in organic spin valves

The effect of lattice dimerization on the magnetoresistance (MR) in organic spin valves is investigated based on the Su-Schrieffer-Heeger (SSH) model and the Green's function method. By comparing with the results for a uniform chain, we find that the dimerization of the molecular chain modifies the monotonic dependence of the MR on the bias to an oscillatory one. A sign inversion of the MR is observed when the amplitude of the dimerization is adjusted. The results also show that at a low bias, the MR through a dimerized chain decreases with the increasing bias as well as the increasing chain length, which is consistent with the experimental reports. A further understanding can be achieved by analyzing the electronic states and the spin-dependent transmission spectrum with the parallel and antiparallel magnetization orientations of the two ferromagnetic electrodes.     

Critical behaviour of an amorphous ferromagnet close to the percolation threshold

A detailed study of the magnetisation, electrical resistivity and ac magnetic susceptibility of the amorphous Fe₃Ni₇₇B₁₈Si₂ alloy has been performed. This alloy is ferromagnetic with the Curie temperature T_c = 19,5 K. Critical exponents δ = 4,9 and α = ?0,51 were obtained from the experiment while γ = 1,66 and β = 0,43 were calculated from the scaling relations. However the effective critical exponent γ ¹ deduced from the initial magnetic susceptibility exhibits a non-monotonic variation with temperature reaching a maximum of about 1.8 around 43 K. The results are discussed in terms of recent theoretical predictions.     

Dynamics of interchain delocalized polarons in polymers

Polaron dynamics in a system of highly ordered conjugated polymer chains is investigated based on the tight binding model. With the interchain coupling enhancing,it takes longer time for the electron added to the system to induce a localized polaron state. Beyond a certain strength of the interchain coupling,the electron evolves into a two-dimensional delocalized polaron state. Dynamical simulations suggest that the well-ordered organic molecule systems with two-dimensional polarons exhibit higher mobilitie...     

链间耦合对聚合物中双激子态反向极化的影响

从紧束缚模型出发，研究了链间相互作用对双激子态反向极化的影响.结果发现：加链间耦合后，双激子态仍主要局域在一条链中.当简并破缺较小时，反向极化程度随耦合强度的增加大幅提高；当简并破缺较大时，反向极化程度随耦合强度的增加基本不变. 关键词： 反向极化 双激子态 链间耦合     

Critical temperature of superconductor/ferromagnet bilayers

Superconductor/ferromagnet bilayers are known to exhibit nontrivial dependence of the critical temperature T _c on the thickness d _f of the ferromagnetic layer. We develop a general method for investigation of T _c as a function of the bilayer parameters. It is shown that interference of quasiparticles makes T _c (d _f ) a nonmonotonic function. The results are in good agreement with experiment. Our method also applies to multilayered structures.     

Critical behaviour of elastically coupled systems with spatially anisotropic critical fluctuations

The spatial anisotropy of critical fluctuations has strong influence on the temperature dependence of the elastic constants of an elastic medium coupled magneto- or electrostrictive to the order parameter. Under pinned boundary conditions we find for uniaxial dipolar systems of hexagonal and trigonal symmetry a second order phase transition, where only c₁₁ and c₁₂ show critical behaviour. For other symmetries a first order transition is expected. At an uniaxial Lifshitz point only c₃₃ becomes critical and the phase transition remains of second order for any symmetry.     

Specific Heat and Charge Density of Quasi-One-Dimensional Interchain Coupling Organic Ferromagnets

On the basis of a generalized SSH model, an organic polymer ferromagnet theory is proposed at the finite temperature in the self-consistent mean field approximation, and the specific heat and charge density of the quasione-dimensional interehain coupling organic ferromagnets are presented. We find that an obvious feature is to present itself the round peak for the specific heat with the temperature. This indicates unambiguously the presence of the phase transition in the system. The transition temperature plays down with increasing of the interchain coupling t2 or decreasing of the electron repulsion u. The curves of charge density with the temperature debase monotonously. This result illustrates that the higher the temperature is, the more electrons are excited.     

高度方向性多光束有机激光

采用DFB分布反馈结构的有机激光由于其自身优点备受关注,而利用高阶布拉格反馈的多光束有机激光及其原理鲜有报道。不同于以往的低阶布拉格反馈形成单波导或单光束激光,本文通过在平面有机半导体波导引入高阶布拉格反馈分别制备了红色和蓝色多束有机激光器。利用四阶布拉格反馈和PVK：DCJTI薄膜实现三光束红光激光器,出射角度为±53°和0.5°。利用五阶布拉格反馈和PS：DSA-ph薄膜实现四光束蓝光激光器,出射角度为±18°和±75°。融合平面波导与光栅耦合的机理,研究了高阶布拉格光栅反馈与器件特性之间的关系。结果表明,理论计算的光束耦合角度和实际测试相符,结果在一定程度上为多光束有机激光器件的设计提供了参考。