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1.
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. 相似文献
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Luis A. Cisneros-Ake Hugo Parra Prado Diego Joselito López Villatoro R. Carretero-González 《Physics letters. A》2018,382(12):837-845
We consider the problem of energy transport in a Davydov model along an anharmonic crystal medium obeying quartic longitudinal interactions corresponding to rigid interacting particles. The Zabusky and Kruskal unidirectional continuum limit of the original discrete equations reduces, in the long wave approximation, to a coupled system between the linear Schrödinger (LS) equation and the modified Korteweg–de Vries (mKdV) equation. Single- and two-hump bright soliton solutions for this LS–mKdV system are predicted to exist by variational means and numerically confirmed. The one-hump bright solitons are found to be the anharmonic supersonic analogue of the Davydov's solitons while the two-hump (in both components) bright solitons are found to be a novel type of soliton consisting of a two-soliton solution of mKdV trapped by the wave function associated to the LS equation. This two-hump soliton solution, as a two component solution, represents a new class of polaron solution to be contrasted with the two-soliton interaction phenomena from soliton theory, as revealed by a variational approach and direct numerical results for the two-soliton solution. 相似文献
5.
A standard statement is that in the interacting electron (exciton) — phonon systems in molecular chains and on the level of the standard quantum mechanics, the formation of localised solition states is energetically more advantageous than the formation of extended (plane--wave-like or polaron) states (see e.g. /1/ for a review). The question about validity of this statement is not yet finally settled /2/. We are going to question this assertion using trivial variational arguments here. For arbitrary localized standing-soliton state (having its energy lower than the states describing running solitons irrespective of technique used to derive them), we are able to prove the existence of an intermediate or large polaron state whose energy is still lower. Hence, the energy arguments are not sufficient to explain the anomalous soliton stability. 相似文献
6.
We have studied the electric-field-driven motion of a polaron by solving the
time-dependent Schr\"{o}dinger equation nonadiabatically and the lattice
equation of motion simultaneously. It is found that the polaron may
experience two sequent transitions under high fields; one is the
transition from the subsonic to the supersonic state, and the other from the
supersonic to dissociated state. The acoustic mode is decoupled from the
charge when the polaron moves at a speed faster than the sound speed, and
then the optical mode is decoupled at the second transition to make the
polaron dissociate completely. 相似文献
7.
Using force constants which have been obtained for the first time from semi-empirical self-consistent-field calculations on various cluster models of periodic trans-polyacetylene and of neutral and charged soliton and polaron defects the infrared and Raman spectrum of undoped and doped trans-polyacetylene is analyzed and interpreted. 相似文献
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This is the second paper in a series devoted to the theorq of soliton and polaron generation in polyacetykne by both radiative and non-radiative processes. The general formalism presented in the first paper of this series which combines the lattice relaxatipn theory of multiphonon processes with the adiabatic self-consistency condition in terms of the Bogoliubovde Gennei equation and the gap equatibn, is applied in this paper to explicit calculation of the non-radiative decay rate of an electron(ho1e) into a plaron and that of an electron-hole pair into a soliton pair in plyacetylene. A heuristic derivation for the formula of non-radiative decay rate is given to elucidate the physical meaning of the approximation invol-ved in the case of low temperature and strong coupling. The matrix elements between multi-electron states are estimated in the Hartree approximation using the single electron states obtained as solutions of the Bogoliubov-de Gennes equation. The result obtained is compared with the numerical calculations on a discrete model. 相似文献
10.
基于一维分子晶体系统的 Holstein 模型,采用压缩-相干态展开方法,计及电子-声子间量子关联和重整化平移修正,分析和研究电子-双声子相互作用对极化子-孤子系统基态性质和量子涨落的影响.推导了一维极化子-孤子系统的封闭形式非线性方程.应用非线性项展开方法,给出非线性方程的解析解和相关基态特性结果.研究表明,仅当电子-双声子耦合强度 g1<0时非线性方程才有孤波解,此时声子量子涨落效应随着压缩的增加,极化子-孤子系统基态能量变得更负,孤子局域减少,孤子态更加稳定;另一方面,电子密度涨落〈Δ2n〉和声子坐标-动量的不确定量〈Δ2p〉〈Δ2q〉比无声子压缩效应的大,极化子结合能变得更负.特别是,当g1<0时,双声子效应的量子涨落〈Δ2n〉与〈Δ2p〉〈Δ2q〉的值比单声子情况有明显增加.
关键词:
压缩-相干态展开
极化子-孤子态与量子涨落
电子-双声子相互作用
非线性薛定谔方程 相似文献
11.
采用数值方法研究了在一个具有扩散效应的光伏光折变晶体中的非相干耦合的亮和暗光伏空间孤子对的偏转特性.结果表明,由于非相干相互作用,晶体中的一个亮孤子和一个暗孤子互相俘获,且两个孤子的中心沿着相同的轨迹移动.发现,当亮孤子的入射峰值强度不变时,通过调节暗孤子的入射背景强度可以控制亮孤子的偏转;当暗孤子的入射背景强度处于一个特殊值时,亮孤子的偏转被抑制,而当暗孤子的入射背景强度偏离这个特殊值时,亮孤子发生偏转.同样,当暗孤子的入射背景强度不变时,其偏转可以通过调节亮孤子的入射峰值强度来控制. 相似文献
12.
基于Su-Schrieffer-Heeger(SSH)模型,考虑电子-电子相互作用,以及在哈密顿量中引入Brazovskii-Kivova对称破缺项,采用动力学演化的方法研究了在外电场作用下共轭高聚物分子链中大极化子与小极化子之间的弹性散射过程.研究发现,载流子的载荷性质不但决定大小极化子之间的相互作用性质,也深刻地影响了其发生散射后的载流子输运性质.在较低电场的作用下,当两载流子电性相同时,发生碰撞后,小极化子将推动着大极化子一起运动;而当两者电性相反时,碰撞后,大极化子将拖曳着小极化子一起运动.当电场强度超过临界值时,将产生量子隧穿效应,即,大小极化子相互迅速穿透,且不受载流子的载荷影响. 相似文献
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The crossover of large to small radius polaron is studied in terms of the inverse-relaxation time and temperature.It is found that the small radius polaron exists at higher temperature than the large radius polaron.A formula which relates the inverse-relaxation time to the ratio of arbitrary temperature and Debye temperature of the crystal is derived.The polaron crossover temperatures in NaCl and KBr are found from plotted graphs.The straight line emerging at the Debye temperature T_d of a graph reflects the increase of the inverse relaxation time for increasing temperature up to the collapse of the small radius polaron.The relationship between the small and large radius polarons is found and known ratios of the effective and the bare masses of the electrons for the two substances are used to validate our results.The small radius polaron's mass is later compared with the mass obtained from the hopping formula and is found to be approximately equal.Finally,we point out that the crossover temperature is material-specific since it depends on the Debye and the effective dielectric function. 相似文献
15.
《中国物理 B》2020,(1)
The propagation characteristic of two identical and parallel dark solitons in a silicon-on-insulator(SOI) waveguide is simulated numerically using the split-step Fourier method. The parallel dark solitons imposed by the initial chirp are investigated mainly by changing their power, their relative time delay. The simulation shows that the time delay deforms the parallel dark soliton pulse, forming a bright-like soliton in the transmission process and making the transmission quality down. By increasing the power of one dark soliton, the energy of the other dark soliton can be increased, and larger increase in a soliton's power leads to larger increase in the energy of the other. When the initial chirp is introduced into one of the dark solitons, higher energy consumption is observed. In particular, positive chirps resulting in pulse broadening width while negative chirps narrowing, with an obvious compression effect on the other dark soliton. Finally, large negative chirps are found to have a profound impact on parallel and nonparallel dark solitons. 相似文献
16.
本文采用扩展Hubbard模型, 加上长程关联哈密顿量,在自然边界条件下用自洽场方法研究了有限长反式聚乙炔链中极化子的问题。计算了长程电子关联对极化子的影响并计算了极化子的长程关联能。计算发现长程电子关联使极化子的位形变宽变浅(局域性减弱),在极化子区域,长程电子关联能比平均长程电子关联能要大。当链长增加到100格点以上时,电子极化子和空穴极化子的平均关联能趋于-0.1663eV,而在极化子区域,电子极化子和空穴极化子的平均关联能趋于-0.1868eV。 相似文献
17.
We investigate the effect of temperature on polaron dynamics in the framework of a tight-binding model. The dissociation of a polaron will become fast with the increase of temperature. There exists a crossover of the charge localization time from strong to weak temperature-dependence. Instead of the uniform motion at zero temperature, a polaron moves un-uniformly under a driven field at a finite temperature, which indicates a discrete hopping between base pairs. It is also found that the polaron motion is thermally activated. A high temperature will result in a fast movement of a polaron under a deriving field. 相似文献
18.
采用一维紧束缚近似的SSH模型,计算了不同强度的电场下高聚物中一个负电极化子和一个三重态激子的碰撞过程.结果表明,碰撞后体系仍保持为极化子和三重态激子状态的几率最大,束缚在极化子缺陷中的电子有较大的几率被激发到导带形成自由电子,另外,三重态激子有一定的几率被极化子湮灭形成极化子激发态.极化子和激子的碰撞对极化子的稳定性有影响,还会使能隙中出现新的能级.由于极化子激发态可以通过辐射跃迁回到基态,因此碰撞会对高聚物的电致发光效率产生一定影响.研究结果对于理解高聚物中极化子的输运性质和高聚物的发光性质具有一定的
关键词:
极化子
激子
高聚物 相似文献
19.
从离散的SSH模型出发,考虑了链内的电子相互作用,以及由杂质和周围链上的荷电孤子产生的库仑势的影响,探讨了各种掺杂浓度的反式聚乙炔中孤子晶格的能谱与电子束缚态。计算结果表明:在孤子晶格的能谱中,在价带底有两条定域能级,在导带顶存在着多个电子束缚态,随掺杂浓度的升高,束缚态的局域性减弱,禁带中的孤子能级形成孤子能带。当掺杂浓度高达16.67%时,所有的电子束缚态都消失,转变为扩展态。孤子晶格的禁带宽度随着掺杂浓度的增加而增大,最高占据态与导带底之间的能隙则随之逐渐减小。孤子能带底与价带顶之间的能隙在临界浓度附近有一极大值。还讨论了电子-电子相互作用对孤子晶格能谱的影响。
关键词: 相似文献
20.
A. É. Myasnikova É. N. Myasnikov 《Journal of Experimental and Theoretical Physics》1999,88(1):101-104
Owing to a funadmentally erroneous approach to calculations of the effective polaron mass (calculations that use a model without
spatial dispersion of the lattice polarizability), the polaron inertial mass has never before been distinguished from the
mass as a measure of kinetic energy. In this paper we derive an expression for the tensor of the inertial mass of a large
polaron. The tensor is found to be fully determined by two components: the longitudinal component, corresponding to the case
where the force acting on the polaron is parallel to the polaron velocity, and the transverse component, corresponding to
the case where the acceleration is perpendicular to the polaron velocity. The components of the polaron inertial mass tensor
depend quasirelativistically on the polaron velocity due to the quasirelativistic compression of the polarization field in
the direction of motion, which constitutes the effect of spatial dispersion of the lattice polarizability. We derive a formula
that approximates the dependence of the components of the polaron mass tensor on all the parameters: the frequency and dispersion
of the phonons, the polaron velocity, and the effective dielectric constant.
Zh. éksp. Teor. Fiz. 115, 180–186 (January 1999) 相似文献