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无限深量子阱中强耦合极化子的基态结合能 总被引:3,自引:0,他引:3
研究了无限深量子阱中极化子的基态性质,采用线性组合算符和变分相结合的方法导出了强耦合极化子的振动频率λ、基态能量E0和基态结合能Eb,讨论了阱宽L和电子-LO声子耦合强度α对强耦合极化子的振动频率λ、基态能量E0和基态结合能Eb的影响。通过数值计算,结果表明:强耦合极化子的振动频率和基态结合能随阱宽L的增大而减小,随电子-LO声子耦合强度α的增强而增大;基态能量随阱宽L的增大而减小,其绝对值随电子-LO声子耦合强度α的增强而增大;当量子阱阱宽L趋近于无限大和无限小两种极限情况下,分别与三维和二维极化子的结果相一致。 相似文献
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研究了磁场作用下石墨烯中电子与表面光学声子弱耦合情况下的极化子的性质。采用线性组合算符和Pekar变分法分别推导出了石墨烯中弱耦合极化子的基态能量E0、第一激发态能量E1和跃迁频率ω随磁场强度B和德拜截止波数kd之间的变化关系。数值计算结果表明,极化子的基态能量E0随磁场强度B变化的曲线(kd一定时)和E0随kd的变化曲线(B一定时)均会分裂成对称的两条,并且当B一定时E0的绝对值随kd的增加而增加。在kd一定时,极化子的第一激发态能量E1和跃迁频率ω均为磁场B的增函数;在B一定时,E1和ω均随kd的增加而增大。 相似文献
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用脉冲激光沉积法在(111)Si衬底上成功制备了高度择优取向的Fe3O4薄膜.电阻-温度关系表明Fe3O4薄膜的Verwey转变(TV)约在122 K,低温段(TV)输运特征满足Mott变程跳跃模型,高温段(T>TV)为小极化子输运.激光作用下的光电导实验发现,在整个温区表现为光致电阻率减小,而且低温段的电阻变化率比高温段要大很多.分析认为Fe3O4薄膜的光致电阻率变化主要与激光激发t2g电子的转移有关.
关键词:
3O4薄膜')" href="#">Fe3O4薄膜
小极化子
光诱导特性 相似文献
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应用紧束缚双带模型对混合卤化物的电荷掺杂性质进行了计算,发现单电荷掺杂在混合卤化物中形成极化子,双电荷掺杂则形成稳定的双极化子;单体的长度和界面耦合都对极化子和双极化子的产生和稳定性有影响.混合卤化物的单体对掺杂电荷具有选择性;电子-电子相互作用并不能使形成双极化子的两个同号电荷相互排斥而形成两个单极化子.在具有电荷自发转移的材料中,混合卤化物单体对掺杂电荷没有像其他混合卤化物一样的选择性,掺杂电荷的定域位置取决于两种单体对该电荷的束缚能力.
关键词:
混合卤化物
极化子
电荷约束 相似文献
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鉴于极化激元对介电环境异常敏感的特性,本文中提出了双曲材料六方氮化硼(hBN)和石墨烯与相变材料二氧化钒(VO2)组成的异质结构,用来研究hBN声子极化激元(PhPs)的主动可调谐性.研究结果表明,通过控制hBN/VO2异质结构中VO2相变可实现对hBN PhPs的主动调谐,获得主动可调谐的自发发射(SE)率.当在hBN/VO2异质结构中添加石墨烯时,会在hBN双曲线带内耦合产生双曲等离子体-声子极化激元(HPPPs),而在双曲线带外产生表面等离子体-声子极化激元(SPPPs),通过控制VO2相态和调节石墨烯化学势亦可实现石墨烯/hBN/VO2异质结构的耦合色散及SE率的主动调谐.该研究为使用诸如相变材料和石墨烯等功能材料调谐各向异性光学材料与光的相互作用机制提供了理论指导. 相似文献
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抛物量子线中弱耦合极化子的有效质量和光学声子平均数 总被引:9,自引:5,他引:4
讨论电子与体纵光学(LO)声子弱耦合时对抛物量子线中极化子性质的影响.采用Tokuda改进的线性组合算符法、Lagrange乘子和变分法,导出了抛物量子线中弱耦合极化子的有效质量和光学声子平均数随拉格朗日乘子变化的规律及极化子振动频率随量子线约束强度的变化规律.并以ZnS量子线为例进行了数值计算,结果表明:抛物量子线中弱耦合极化子的有效质量m*和光学声子平均数N随着拉格朗日乘子u的增加而增大;该结论与体材料中结论基本一致,但量子线中的效应比体材料更明显,表明量子线对电子约束的增强,使极化子效应更明显.同时,极化子振动频率λ随约束强度ω0的增强而增大. 相似文献
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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
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XiaoFeng Pang 《中国科学G辑(英文版)》2008,51(3):258-268
A new variational-ansatz of states of electrons and phonons was proposed on the basis of the Holstein model in strongly coupled
electron-phonon systems for studying the influence of nonadiabatic phonon fluctuation, arising from the motion and density
fluctuation of electrons, on the properties of ground state, uncertainty relation, stability of polarons, charge density wave
(CDW) and phonon staggered ordering. The new ansatz represents the correlation among the displacement and squeezing states
of phonons and polaron’s state of electrons as well as the squeezing-antisqueezing effect. The correlation and squeezing-antisqueezing
effect result in the decrease of ground state energy, enhancement of stability of the systems, increase of binding energy
of the polarons, weakening of the growing speed of polaron narrowing of the electron band, increase of the charge density
wave order and suppression of the increased tendency of anomalous quantum fluctuation of the phonons in such a case, when
compared with the uncorrelated case in the systems. The results obtained show that the ground state determined by the new
state ansatz is most stable, thus the new ansatz describing the properties of the coupled electron phonon systems is very
relevant and available, especially in strongly coupled and largely squeezed cases.
Supported by the National “973” Project of China (Grant No. 2007CB6103) 相似文献
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We calculate the infrared absorption of large polarons bound to defects in the weak coupling limit. Polar crystals with more than one longitudinal optical phonon branch coupled to the electrons are considered. Oscillator strengths corresponding to defect transitions without phonons and to transitions with emission of phonons are calculated using the Larsen wave-functions. The results are applied to infrared data in strontium titanate and it is found that weak coupling calculations are in better agreement than strong coupling ones. 相似文献
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We report transport measurements through graphene on SrTiO(3) substrates as a function of magnetic field B, carrier density n, and temperature T. The large dielectric constant of SrTiO(3) very effectively screens long-range electron-electron interactions and potential fluctuations, making Dirac electrons in graphene virtually noninteracting. The absence of interactions results in an unexpected behavior of the longitudinal resistance in the N=0 Landau level and in a large suppression of the transport gap in nanoribbons. The "bulk" transport properties of graphene at B=0 T, on the contrary, are completely unaffected by the substrate dielectric constant. 相似文献
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We extend the theory of large polarons in the frame of a semi classical model. We analyse two physical effects in which the discreteness of the periodic lattice plays a major role: i) In addition to standard Holstein polarons, we show the existence of braggons which are polarons whose energy lies in a lattice gap. According to the type of gap considered, some of the them are ordinary solitons, some others are vector-solitons. ii) The pinning (or Peierls Nabarro) effect of the lattice on the polarons. We show that the coupling of the electrons with acoustic phonons is able to produce polarons or bipolarons in crystallographic situations where the coupling with optical phonons does'nt. The existence of multidimensional polarons and bipolarons is investigated, and we find interesting possibilities in dimension D=2. The binding energy and effective mass of the polarons are determined in the frame of the model, and their dynamical stability is analysed. We also show the existence, for D=1, of tripolarons in which two energy levels are occupied in the potential well created by the electron-lattice interaction. Finally the conditions of validity of the semi-classical approximation are given. 相似文献
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用改进的Lee-Low-Pines变分方法研究纤锌矿In0.19Ga0.81N/GaN量子阱结构中束缚极化子能量和结合能等问题,给出基态结合能、不同支长波光学声子对能量和结合能的贡献随阱宽和杂质中心位置变化的数值结果.在数值计算中包括了该体系中声子频率的各向异性和内建电场对能量和结合能的影响、以及电子和杂质中心与长波光学声子的相互作用.研究结果表明,In0.19Ga0.81N/GaN量子阱材料中光学声子和内建电场对束缚极化子能量和结合能的贡献很大,它们都引起能量和结合能降低.结合能随着阱宽的增大而单调减小,窄阱中减小的速度快,而宽阱中减小的速度慢.不同支声子对能量和结合能的贡献随着阱宽的变化规律不同.没有内建电场时,窄阱中,定域声子贡献小于界面和半空间声子贡献,而宽阱中,定域声子贡献大于界面和半空间声子贡献.有内建电场时,定域声子贡献变小,而界面和半空间声子贡献变大,声子总贡献也有明显变化.在In0.19Ga0.81N/GaN量子阱中,光学声子对束缚极化子能量和结合能的贡献比GaAs/Al0.19Ga0.81As量子阱中的相应贡献(约3.2—1.8和1.6—0.3 meV)约大一个数量级.阱宽(d=8 nm)不变时,在In0.19Ga0.81N/GaN量子阱中结合能随着杂质中心位置Z0的变大而减小,并减小的速度变快.随着Z0的增大,界面和半空间光学声子对结合能的贡献缓慢减小,而定域光学声子的贡献缓慢增大. 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
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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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Q.-H Chen Y.-H. Ren Z.-K Jiao 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(3):307-313
The general properties of one-dimensional large Fr?hlich polarons in motion are investigated with the previous extended coherent
states where two-phonon correlations are considered. As a result, the polaron energy, velocity, effective mass, and average
number of virtual phonons as a function the polaron total momentum are evaluated in a wide range of the coupling constant.
In addition, rich information about virtual phonons emitted by the electron in motion is obtained. More importantly, some
intrinsic features of 1D moving polarons are presented for the first time, which may also be suited to moving polarons in
more than one dimensions.
Received: 23 October 1997 / Revised and Accepted: 27 January 1998 相似文献