孤子振动模的定域性

对于聚乙炔中孤子的五个定域振动模,本文研究了它们的位形随链长的变化而演变的情况,从而可确定其定域性。本文同时考察了开链和闭环两种情况。对于闭链,五个定域模定域于孤子附近,其形状与链长无关。对于开链,定域模g₁,g₂,g₃和g₅的位形不随链长而改变,因而是完全定域的,但是g₄的两翼随链长增加而变宽,定域性不完全。 关键词：     

电子关联和孤子

聚乙炔中的电子关联和孤子可用相关基函数方法(CBF)来研究,通过考虑完全的电子-电子相互作用,得到含有单个电荷的奇数原子链的稳定位形为孤子的结论,随着电子-电子互作用强度U和互作用程α/β的增加,孤子定域性加强,产生能降低,因此,即使计入电子-电子相互作用,孤子仍然是导电聚合物中的主要载流子。 关键词：     

链间耦合对反式聚乙炔中孤子能谱及其局域振动模的影响

从计及了链间相互作用项的ＳＳＨ模型出发，讨论了相邻两条链间电子跃迁对反式聚乙炔中孤子能谱及孤子附近的局域振动模的影响，结果发现：（１）孤子能级偏离了禁带中心，能谱的对称性被破坏。（２）局域振动模发生劈裂，劈裂后两模的振动位形具有与原模相同的结构，但它们的频率和最大振幅均不同于原局域模。另外，模的频率还与两条链上的孤子类型以及链的相对序列有关。 关键词：     

TWO-DIMENSIONAL LOCALIZED MODES IN CONJUGATED POLYMERS: THE NONLINEAR ELECTRON-PHONON COUPLING EFFECT

The two-dimensional localized modes around a soliton have been investigated by using an extension of Su-Shrieffer-Heeger model, in which is included the nonlinear term of electron-phonon interaction. The results show that there appears an additional localized mode, and the two modes obtained in the previous work without the nonlinear term disappear. Furthermore, the frequencies of the modes are shifted and their localizations are changed after turning on the nonlinear term.     

次近邻电子跳跃对孤子的电子束缚态和孤子附近局域模的影响

从SSH模型出发,考虑电子次近邻跳跃的影响,研究了聚乙炔中孤子的电子束缚态和孤子附近的局域振动模。结果发现:1.电子能谱中的电子-空穴对称性消失;2.孤子的电子束缚态的数目和位置发生了变化,且与孤子的类型有关;3.孤子附近出现了一个新的局域振动模G₆;4.次近邻电子跳跃改变了局域模的频率,增强了局域模的局域性。 关键词：     

Dynamics of self-localized excitations in a polyacene chain

Dynamical formation processes of self-localized excitations induced by charge injection or photoexcitations in a polyacene chain are investigated by a nonadiabatic dynamic method. The polyacene chain is treated as two alternatively coupled polyacetylene chains. The initial lattice configuration is taken as the pristine polyacene chain. It contains an interchain-coupled neutral soliton as a consequence of odd-number sites in each of the two chains. The nonadiabatic dynamical processes are carefully investigated in the following physical cases: (1) electron injection; (2) electron transition from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO); (3) electron transition from HOMO to the localized soliton level, and (4) electron-hole pair excited at the continuum absorbtion edge for light polarized parallel to the chain. It is interestingly found that the centers of the electron and the hole excited by light polarized parallel to the chain are separated. Therefore, the photogenerated charge carriers should be favorable in polyacene, which is remarkably different from those found in a single polyacetylene chain.     

Lattice vibrational analysis of polyacene

Within an extended Su-Schrieffer-Heeger model, we made a lattice vibrational analysis of polyacene. In a singly-charged polyacene, the ground state contains an interchain-coupled polaron of quasi-D2h symmetry, around which we found thirteen localized modes in total. Among these localized modes, five (three B2u and two B3u) are infrared active, six (four Ag and two B1g) modes are Raman active, and the other two localized modes are asymmetric, which are both infrared active and Raman active. For the case a charged polaron is coupled with a neutral soliton in a finite polyacene chain, the vibrational modes are also calculated to display the coupling effect between self-trapping excitations on phonons. It is found that the localized phonons are determined mainly by the charged polaron, but the number and frequencies of the localized modes are influenced by the existence of the neutral soliton.     

The vibrational modes around the soliton lattice with next neighbor hopping interactions in highly doped trans-(CH) x

Starting from the extended SSH model that includes an external Coulomb potential arising from interchain charged solitons and counterions, the intrachain e-e interaction and the next neighbor hopping interactions, eight localized vibrational modes around the soliton lattice have been found for the doping levels from 3.33 at.% to 13.33 at.%. Among them three are infrared active and they can be used to interpret the three observed infrared absorption lines at 487, 1284 and 1362 cm^–1. Furthermore, the frequencies of localized modes are decreased and their localizations are weakened when the dopant concentrations increase.     

低维凝聚态物理的进展(Ⅱ)聚合物中的元激发

本文介绍八十年代以来在聚合物研究中提出的新物理概念——各种非线性元激发。静态的有孤子、极化子、双极化子和孤子晶格;动力学的有呼吸子和定域振动模。本文着重描绘这些元激发的物理图景以及与实验现象之间的关系,适当给出基本的理论公式。     

Optical conductivity of solitons in polyacetylene

The soliton lattice solution of the continuum model for polyacetylene is used to derive the frequency dependent conductivity of charged solitons. The limit of low soliton density is explicitly evaluated and shown to be free of singularities. The conductivity sum rule is proven for the model Hamiltonian, and is shown to be satisfied by the explicit solution. Implications for polyacetylene and for TTF-TCNQ are discussed.     

Infrared transmission spectra of oxygen-exposed polyacetylene films

The oxidation process of polyacetylene films which are very sensitive to exposure to oxygen was studied by infrared spectroscopy as a function of the exposure time. The absorption bands at 900 and 1370 cm⁻¹ which were assigned to dopant induced modes were also observed in oxygen-exposed trans-polyacetylene. The number of absorption centers was reversible on pumping. These results indicate that adsorbed oxygen acts as a dopant and generates a charged soliton.     

Density matrix renormalization group studies on one-dimensional -conjugated organic ferromagnet with side radicals

By using the density matrix renormalization group (DMRG) and the self-consistent numerical method, we obtain a high spin ground state with localized spin density describing spin localization and the soliton describing the distortion of the lattice configurations along the main chain. Different electron-phonon interactions result in different configurations of solitons. When the electron-phonon coupling along the main chain is larger than a critical value , a transition from a single soliton-like distortion to a pair of soliton-like distortions along the main chain takes place. Such critical value depends mainly on the intersite Coulomb interactions. The spin density wave along the main chain is always localized around the center of soliton-like distortions. Received 2 July 2001 and Received in final form 25 September 2001     

Baryon resonance as fluctuations of the skyrme soliton

Normal modes of fluctuations around the static Skyrme soliton solution are investigated. They carry an unconventional quantum number I, which is the sum of orbital angular momentum and isospin of the asymptotic pion field and which serves well as a label for experimentally observed resonances. From the calculated phase-shift positions and widths of corresponding baryon resonances are extracted.     

Feshbach resonance management for Bose-Einstein condensates

An experimentally realizable scheme of periodic sign-changing modulation of the scattering length is proposed for Bose-Einstein condensates similar to dispersion-management schemes in fiber optics. Because of controlling the scattering length via the Feshbach resonance, the scheme is named Feshbach-resonance management. The modulational-instability analysis of the quasiuniform condensate driven by this scheme leads to an analog of the Kronig-Penney model. The ensuing stable localized structures are found. These include breathers, which oscillate between the Thomas-Fermi and Gaussian configuration, or may be similar to the 2-soliton state of the nonlinear Schr?dinger equation, and a nearly static state ("odd soliton") with a nested dark soliton. An overall phase diagram for breathers is constructed, and full stability of the odd solitons is numerically established.     

Chain length dependence of localized vibrational modes around a soliton in trans-polyacetylene

Vibrational frequencies of finite polyacetylene with a charged soliton are calculated using the molecular orbital method. It is found that the frequency of the translational mode has a remarkable length effect and is inversely proportional to the square of chain length. The dependence is explained by regarding the soliton as a quantum particle in a one dimensional box.     

Effects of the coulomb interaction on the 2D localized modes of soliton in the photoexcited polyacetylene

We have studied the effects of electron-electron interaction on the 2D localized modes of a soliton using the two-dimensional model that includes the bond-bending term and pinning effects in the photoexcited samples. The result shows that seven localized modes always exist, but the frequencies slightly move for different parameter and their localization are strengthened.     

Localized vibrational modes around solitons in coupled trans-polyacetylene chains

The effects of interchain coupling have been studied on the localized vibrational modes around a soliton in doped and photoexcited samples of trans-(CH)_x by using an extension of the SSH model in which two neighboring chains modeled individually by SSH Hamiltonian and coupled by an interchain electronic transfer term are considered. The electronic pinning is also included within this model. The localized modes obtained in the SSH model are split and their frequencies are shifted after turning on the interchain coupling. Furthermore, our result can account for the three strong infrared lines at 900, 1260 and 1370 cm^?1 along with a weaker peak at 1150 cm^? r in the optical absorption spectra of lightly doped samples.     

Internal Modes of Relativistic Solitons

We apply a linear perturbation analysis to investigate the relationship between soliton oscillations and the integrability of nonlinear PDEs in bi-dimensional spacetime. For this purpose, we consider a localized solution of the nonlinear differential equation, and study small amplitude fluctuations around it. The linearized equation is a Schrödinger-like, eigenvalue problem. By considering several nonlinear PDEs, which are known to have soliton and solitary wave solutions, we find that in systems which are integrable, this eigenvalue equation has one and only one bound state with zero frequency. Non-integrable equations—in contrast—show extra bound states. The time evolution of the oscillations are also calculated, using a numerical program to integrate the time-dependent equation. The behavior of the modes are studied, using the Fourier transform of the evolving solutions.     

Time-dependent solutions with localized energy of the Einstein system of equations and a nonlinear scalar field

A soliton-like time-dependent solution in the form of a running wave is derived of a self-consistent system of the gravitational field equations of Einstein and Born-Infeld type of equations of a nonlinear scalar field in a conformally flat metric. This solution is localized in space and possesses a localized energy. It is shown that both the gravitational field and the nonlinearity of the scalar field are essential to the presence of such a localized solution. In recent years various classical particle models have been widely discussed which are static or time-independent solutions of nonlinear equations with localization in space and which possess a finite field energy. In particular, soliton solutions [1], solutions in the form of eddies [2], and so on have been derived and investigated. All these solutions were treated in a flat space-time. It is of interest to derive the analogous particle-like solutions with the gravitational field taken into account; in particular it is of interest to investigate the roles of the gravitational field in connection with the formation of localized objects. These problems have been discussed in [3] in the static case. We will present below a soliton-like time-dependent solution in the form of a solitary running wave as an example of the inter-action of a Born-Infeld type of nonlinear scalar field and an Einstein gravitational field in a conformally flat metric.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 12–17, May, 1979.     

Amplitude recurrence of the staggered mode in nonlinear diatomic macro-lattice

The staggered soliton mode, which was first discovered in polyacetylene, was observed by Lou et al. in a one-dimensional nonlinear pendulum-lattice. Some recurrence phenomena of the amplitude of the staggered mode in a macro-lattice system are investigated. The experimental result shows that the amplitude of the envelope soliton changes periodically or quasiperiodically under suitable excited parameters. In addition, a period doubling bifurcation is also observed.