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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. 相似文献
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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。 相似文献
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A polaron state of an electron in a hybrid system composed of a two-dimensional electron gas and a Bose–Einstein condensate of excitons situated in a quantum well coplanar with the electron gas has been investigated. It has been shown that self-localization is possible even at a weak coupling between the components of the structure, when a fluctuation of the density of excitons producing a potential well for the electron is small compared to their average density. 相似文献
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量子点中强耦合极化子的性质 总被引:8,自引:3,他引:5
采用Pekar类型的变分方法研究了抛物量子点中强耦合极化子的基态和激发态的性质。计算了基态和激发态极化子的结合能、光学声子平均数和极化子的共振频率。讨论了这些量对有效限制强度和电子 体纵光学声子耦合强度的依赖关系。结果表明:抛物量子点中极化子的共振频率、基态和激发态极化子的结合能以及光学声子平均数都随量子点的有效束缚强度的增大而减小。光学声子平均数随电子 体纵光学声子耦合强度的增加而增大。 相似文献
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《Annals of Physics》1985,163(1):78-119
Various aspects of the electron-LO-phonon interaction effects on the electronic properties of a single two-dimensional electron layer (as occurring, for example, in artificially structured single quantum wells or heterojunctions made of III–V or II–VI semiconducting materials) are discussed theoretically. In particular, perturbation theory is carried to the second order in the coupling constant to obtain the two-dimensional polaron energy in the weak-coupling limit. Intermediate coupling (the so-called Lee-Low-Pines theory) and strong coupling theories for the two-dimensional polaron problem are developed and interpolation (Padé approximations) formulae valid for arbitrary coupling are derived. Effects of the band non-parabolicity and of the free-carrier screening on the weak-coupling theory are discussed. The real and the imaginary parts of the two-dimensional polaron self-energy are obtained in a many-body perturbation calculation. Comparison with the known three-dimensional results is made wherever possible, showing that the electron-LO-phonon interaction effects are substantially enhanced in confined structures. Explicit formulas valid for two-dimensional systems are given for various polaron parameters like the binding energy, the effective mass, the scattering rate, the average phonon density in the polaron cloud, etc. 相似文献
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Z. An B. Di H. Zhao C. Q. Wu 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(1):71-77
Within an one-dimensional tight-binding model, we
investigate the inelastic scattering processes of oppositely
charged polarons in conjugated polymers under the influence of an
external electric field, by using a nonadiabatic evolution method.
It is found that the polaron pair does not necessarily scatter
into an entity(neutral exciton), but a mixed state composed of
both polarons and excitons. The yield of the neutral exciton
depends sensitively on the strength of applied fields.
Additionally, effects of interchain coupling on the scattering
processes are also discussed, which shows that the interchain
coupling is of fundamental importance and facilitates the
formation of the polaron-exciton. 相似文献
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弱耦合多原子半无限晶体中磁极化子的激发能量 总被引:1,自引:1,他引:0
近年来国内外对多原子极性晶体中磁极化子性质的研究十分活跃,Zorkani等采用变分法计算了束缚磁极化子的基态能量,Kandemir等采用束缚朗道态讨论了二维大磁极化子的基态和第一激发态能量,国内一些学者采用微扰法和新颖算符法讨论了多原子极性晶体中表面和体磁极化子的性质。采用线性组合算符和幺正变换,研究磁场中多原子半无限极性晶体中电子和光学声子弱耦合相互作用所产生的极化子的第一激发态能量及平均声子数。结果表明:当电子无限接近晶体表面时,磁极化子的基态能量仅为Landau能量;第一激发态能量为Landau基态能量的2倍;平均声子数等于各支与电子耦合的体光学声子数和表面光学声子数之和。而当电子处于晶体深处时,磁极化子的基态能量却为Landau基态能量与各支体光学声子以及表面光学声子分别耦合的能量之和;第一激发态能量仍为Landau基态能量的2倍;平均声子数等于各支与电子耦合的体光学声子数和与所处深度有关的各支体光学声子数之和,而与各支表面光学声子无关。 相似文献
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二维声学极化子的基态能量和有效质量 总被引:1,自引:1,他引:0
自陷电子对了解光电材料的光学性质非常重要.近些年来,形变晶格中电子自陷的问题受到研究人员的广泛关注.电子既与声学模耦合,也与光学模相互作用,但电子由自由态向自陷态的转变缘于近程的电子-声学声子耦合.研究表明:声学极化子在大多数半导体以及Ⅲ-Ⅴ族化合物,甚至碱卤化物中都不可能自陷.另一方面,电子-声子耦合在束缚结构,如二维、一维系统中,会有所增强.换言之,电子在低维结构中更容易自陷.Farias等人指出:声学极化子在二维系统中自陷的临界电子-声子耦合常数为定值,不随声子截止波矢的变化而改变.这种结论在物理上不尽合理.通过计算二维系统中的声学极化子基态能量和有效质量,讨论了二维声学极化子自陷问题.研究发现,二维声学极化子自陷转变的临界耦合常数随声子截止波矢的增加朝电子-声子耦合较弱的方向变化.这一特征与前人关于体和表面极化子研究获得的结论定性一致.所得二维声学极化子基态能量的表达式与Farias等人一致,但自陷的结果与Farias等人的结果在定性和定量上均有不同,我们认为Farias等人关于二维声学极化子自陷转变点的确定方式有不妥之处.通过改进自陷转变点的确定方式,得到了在物理上更合理的结果. 相似文献
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强耦合表面极化子的激发能量 总被引:4,自引:2,他引:2
采用线性组合算符方法及幺正变换方法研究了电子与表面光学(SO)声子和体纵光学(LO)声子均为强耦合的表面极化子的激发态性质.计算了体系的有效哈密顿量、振动频率和体系由基态向第一激发态跃迁所需的激发能量. 相似文献
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赵翠兰 《原子与分子物理学报》2013,30(6)
采用求解能量本征方程、幺正变换及变分相结合的方法,研究声子和温度对球型量子点中极化子性质的影响。数值计算表明,声子效应导致极化子的基态能量低于电子能量,且极化子基态能量随电子—声子耦合强度的增大而降低。数值计算还表明,温度较低时,声子不会被激发,极化子的基态能量不随温度而变;温度较高时,声子会被激发,导致极化子能量随温度升高而增大。 相似文献
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A. J. Dahm 《Zeitschrift für Physik B Condensed Matter》1995,98(3):333-336
Three novel states of electrons on a helium film are described. The first is a diplon, an electron trapped by a positive charge located on a substrate beneath the film, the second is a variation of the first leading to the possibility of a two-dimensional metal-insulator transition, and the third is a ripplonic polaron, an electron self-trapped in a surface dimple. From a survey of experimental searches for the ripplonic polaron state I conclude that no polaron transition occurs on films thicker than 14 nm at T>1.5 K. 相似文献
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A variational scheme of the Pekar type is employed to study the strong-coupling optical polaron on the outer surface of the polar crystal under the influence of a magnetic field. The ground state energy and the effective mass of the polaron are obtained as functions of the magnetic field strength and the electron-surface optical phonon coupling constant. It is shown that the effective mass of the surface polaron appears in nonisotropic nature due to the coupling between the electron and the surface optical phonon. 相似文献
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《Annals of Physics》1986,166(1):93-163
We have studied the dynamics and transport relaxation of a large polaron in a one-dimensional (1-D) system with an acoustic- (Debye) type phonon spectrum and a deformation potential electron-phonon interaction. The dynamics is treated in a collective coordinate formalism which shows that such a polaron moves as a heavy quasi-particle that carries energy and (crystal) momentum. For thermal energies less than the polaron binding energy, its transport relaxation is dominated by collision processes wherein a thermal phonon is reflected off the polaron with a momentum transfer that is small compared to the thermal polaron momentum. The phonon reflectivity is estimated and found to exhibit a maximum (resonance) for phonon wavelengths that match the polaron size. Furthermore, the reflectivity is largely independent of the polaron momentum. We incorporate these results into a semi-classical (Boltzmann) kinetic theory and obtain a polaron mobility that is independent of the polaron effective mass and decreases monotonically with increasing temperature. These results are compared to and found to be substantially different from those obtained recently for the large polaron in the 1-D molecular cystal model wherein the underlying phonon spectrum has optical (Einstein) character.To study the effects of three-dimensional (3-D) coupling on the 1-D polaron, we propose a simple 3-D extension of the 1-D acoustic model which includes both electronic and elastic interchain interactions. We briefly discuss the question of polaron stability in the presence of 3-D coupling and the criteria of validity for the purely 1-D treatment. 相似文献
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S. A. Gordyunin A. M. Belemouk A. E. Karakozov A. F. Barabanov 《Journal of Experimental and Theoretical Physics》2002,94(1):135-148
The optical spectrum of the normal state of a doped two-dimensional antiferromagnet is analyzed in a Kondo lattice model with regard to the complex structure of a spin polaron. The optical properties are determined by sharply anisotropic scattering of spin-polaron excitations by antiferromagnetic fluctuations of a system of localized spins. It is shown that the relaxation of carriers in the infrared range is mainly attributed to the strong coupling between these carriers and the mode of low-frequency spin excitations with the quasimomentum close to the antiferromagnetic vector Q=(π,π). The latter coupling is associated with the fact that the regions of the Fermi surface of the lower polaron band are close to the boundary of the antiferromagnetic Brillouin zone. The calculated optical characteristics are in qualitative agreement with experimental data for the normal state of high-temperature superconductors (HTSCs). 相似文献
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声子和温度对球型量子点中极化子性质的影响 总被引:1,自引:0,他引:1
采用求解能量本征方程、幺正变换及变分相结合的方法,研究声子和温度对球型量子点中极化子性质的影响.数值计算表明,声子效应导致极化子的基态能量低于电子能量,且极化子基态能量随电子-声子耦合强度的增大而降低.数值计算还表明,当温度较低,使得电子热运动能量小于声子能量时,声子不会被激发,极化子的基态能量不随温度的变化而变化;在温度较高,使得电子热运动能量大于声子能量时,电子和晶格热运动加剧,更多的声子被激发.极化子的基态能量随温度的升高而增大. 相似文献