广义Fibonacci准周期结构声子晶体透射性质的研究

提出了一维广义Fibonacci准周期结构的声子晶体模型. 对弹性波通过该一维准周期结构声子晶体的透射系数进行数值计算,并与周期结构和标准Fibonacci准周期结构声子晶体的透射系数进行比较. 结果表明,利用一维广义Fibonacci准周期结构的声子晶体可获得比周期结构和标准Fibonacci准周期结构声子晶体更大的带隙范围,同时在带隙内有更丰富的局域模式存在. 对局域模性质的研究有助于声波或弹性波滤波器的制作. 关键词： 广义Fibonacci准周期结构 声子晶体 局域化     

一维压电Fibonacci类准周期声子晶体传输特性

基于传输矩阵法研究了一维压电Fibonacci类准周期声子晶体的传输特性, 比较了一维Fibonacci序列压电准周期声子晶体与非压电准周期声子晶体以及压电周期性声子晶体的透射性. 计算结果表明:弹性波通过一维准周期结构压电声子晶体时与周期性声子晶体一样会有带隙的出现, 且发现具有压电性的Fibonacci序列准周期声子晶体禁带宽度发生了展宽. 进一步讨论了入射角度对固定频率下声子透射系数的影响,结果表明一维压电Fibonacci序列准周期结构声子透射性依赖于入射角度的选取.     

缺陷对准周期磁超晶格输运性质的影响

研究了缺陷结构的Fibonacci磁超晶格的输运性质.结果表明,缺陷结构对纳米准周期链的电子输运性质有重要影响,特别是低能区电子输运 关键词： 缺陷 Fibonacci链 磁纳米结构 输运性质     

弹性波通过一维复合材料系统的透射性质

提出了不同结构的一维弹性波复合材料系统模型,包括一维周期结构声子晶体、标准Fibonacci准周期结构声子晶体、广义Fibonacci准周期结构声子晶体以及完全无序结构的复合材料系统. 采用模式匹配理论法,数值计算了弹性波通过一维复合材料系统的透射系数. 计算结果表明,利用特殊的准周期结构声子晶体可获得比周期结构声子晶体更宽的带隙范围,准周期结构排列的复合材料系统相当于在周期结构中引入了缺陷体一样,带隙内出现了丰富的局域模式. 对弹性波/声波在复合材料系统中局域态性质的研究有助于弹性波/声波滤波器、导波器 关键词： 弹性波复合材料 局域化     

自旋-轨道耦合玻色-爱因斯坦凝聚体激发谱及其有效调控

利用Bogoliubov理论研究了自由空间中可调自旋-轨道耦合玻色-爱因斯坦凝聚体(Bose-Einstein condensates, BECs)的激发谱.通过高频近似得到具有两体相互作用时与时间无关的有效Floquet哈密顿量,从而获得一种可调的自旋-轨道耦合和一种可由周期驱动拉曼耦合调控的有效两体相互作用.基于系统有效的Floquet哈密顿量,得到凝聚体具有相互作用时的色散关系,发现周期驱动强度可以有效地调控色散关系的结构,即周期驱动的拉曼耦合可以调控系统在零动量相与平面波相之间的相变.进一步利用Bogoliubov理论得到系统的Bogoliubov-de-Gennes (BdG)方程,分别研究了凝聚体在零动量相和平面波相中的激发谱.发现零动量相中的激发谱均为声子激发,且激发谱随周期驱动强度的增加表现出贝塞尔函数的行为;平面波相中的激发谱存在声子激发和旋子激发,当周期驱动强度增加时,旋子模出现软化现象.因此,可以通过周期驱动拉曼耦合实时地调控自旋-轨道耦合BECs激发谱中的声子激发和旋子激发.     

正方点阵上Fibonacci超元胞声子晶体的带结构

用平面波展开方法研究了水柱体作为填充物, 按照二维Fibonacci排列成超元胞填充在Hg基体中构成的声子晶体的声频带结构. 结果发现, 随着超元胞中准晶格常数的变化, 各个能带均出现三分裂. 对声场分布的研究发现了居间态的存在. 这些现象体现了准周期结构的特征. 关键词： Fibonacci排列 声子晶体 能带结构     

准周期原胞超晶格中的横声子谱

本文计算了准周期原胞超晶格中横弹性波的体和面模式的色散关系,导出了用传输矩阵表述的动力学格林函数,并用以计算了热涨落的谱密度。结果表明由于系统对于垂直于超晶格轴的平面不存在反映对称性,当表面截取在原胞内F_m个不同的界面上时(F_m是Fibonacci数)半无限样品的横声子表面谱呈现F_m种截然不同的形式。     

一维电声系统中的自旋-电荷分离

文章作者结合团簇微扰理论和优化声子基近似的方法，通过单电子谱函数的计算，研究了一维关联系统中声子效应对自旋-电荷分离的影响，发现由于有限声子频率带来的推迟效应抑制自旋-电荷分离，使之在谱函数中不可见，同时还得到电子对和极化子劈裂的信息。     

铁基非晶态因瓦合金的声子谱研究

用非弹性中子散射实验方法研究了非晶态Ｆｅ_９０－ｘＣｏ_ｘＺｒ_１０（ｘ＝１０，４０）和Ｆｅ_８０－ｙＣｒ_ｙＰ_１３Ｃ_７（ｙ＝４，８）合金的广义声子谱，在低能区域（?ω≤２０ｍｅＶ）观察到了与因瓦效应相关的声子谱软化现象。初步讨论了这种动力学方面的反常行为。结果表明，声子谱软化可能与在因瓦合金中存在增强的电子－声子相互作用有关。 关键词：     

准周期Fibonacci超晶格的低频纵声学模喇曼光谱

本文报导了准周期 Fibonacci 金属 Nb/cu 和非晶半导体 a-Si:H/a-SiN_x:H(x≈1)超晶格纵向低频声学声子模的喇曼散射研究。在弹性连续模型的基础上,理论模拟表明了这些低频声子光谱是对应于周期超晶格中声学模在约化布里渊区的折叠效应。     

二维Fibonacci准晶电子能谱

基于重整化群技术,我们用分解-消元方法研究二维Fibonacci准晶电子能谱性质,得到了具有多种分支结构的能谱,这与一维Fibonacci的单一分支结构完全不同。同时,利用晶格的四重旋转对称性将哈密顿量化简,然后进行数值模拟计算,计算结果与分析结果完全一致。 关键词：     

Electronic properties of quasiperiodic Fibonacci chain including second-neighbor hopping in the tight-binding model

We present an exact real-space renormalization group (RSRG) scheme for the electronic Green's functions of one-dimensional tight-binding systems having both nearest-neighbor and next-nearest-neighbor hopping integrals, and determine the electronic density of states for the quasiperiodic Fibonacci chain. This RSRG method also gives the Lyapunov exponents for the eigenstates. The Lyapunov exponents and the analysis of the flow pattern of hopping integrals under renormalization provide information about the nature of the eigenstates. Next we develop a transfer matrix formalism for this generalized tight-binding system, which enables us to determine the wave function amplitudes. Interestingly, we observe that like the nearest-neighbor tight-binding Fibonacci chain, the present generalized tight-binding system also have critical eigenstates, Cantor-set energy spectrum and highly fragmented density of states. It indicates that these exotic physical properties are really the characteristics of the underlying quasiperiodic structure. Received 5 April 1999     

广义的一维Fibonacci结构

本文提出一维k组元的Fibonacci结构,它包含k个无公度的基本长度,是具有两个基本长度的标准Fibonacci结构的自然推广,投影理论被用来处理它的X射线衍射花样及其指标化问题,理论模拟被用于验证投影理论的结果,值得注意的是,对于有限的链长,当k足够大时,它的衍射谱将趋于混沌。 关键词：     

Electronic spectrum of a two-dimensional Fibonacci lattice

The electronic spectrum and wave functions of a new quasicrystal structure—a two-dimensional Fibonacci lattice—are investigated in the tight-binding approximation using the method of the level statistics. This is a self-similar structure consisting of three elementary structural units. The “central” and “nodal” decoration of this structure are examined. It is shown that the electronic energy spectrum of a two-dimensional Fibonacci lattice contains a singular part, but in contrast to a one-dimensional Fibonacci lattice the spectrum does not contain a hierarchical gap structure. The measure of allowed states (Lebesgue measure) of the spectrum is different from zero, and for “central” decoration it is close to 1. The character of the localization of the wave functions is investigated, and it is found that the wave functions are “critical.” Zh. éksp. Teor. Fiz. 116, 1834–1842 (November 1999)     

Fibonacci链的电子结构特性

对由递推关系S_m+1={S_m|S_m-1}生成的Fibonacci链,从Anderson紧束缚模型出发,用负本征值理论及三对角高阶厄米矩阵本征值理论,对电子的态密度和能级结构进行数值研究,直观简洁地论证其三分叉的能带结构.用重整化群方法,结合散射理论,研究链中电子的局域长度和输运系数,发现具有不同局域属性的能态.一些特定的能量区间值存在扩展态,其相应的输运系数接近1.绝大部分能量对应的电子具有很小或几乎为零的局域长度,说明链中存在相当数量的局域态.定性得出电子输运系数随Fibonacci链参数变化的规律.     

ELECTRONIC ENERGY SPECTRUM STRUCTURE OF THE TWO-DIMENSIONAL FIBONACCI QUASILATTICES WITH THREE KINDS OF ATOMS AND ONE KIND OF BOND LENGTH

After establishing the method of constructing a class of two-dimensional Fibonacci quasi-lattices, by means of a decomposition-decimation method based on the renormalization-group technique, we have studied the rule. of energy spectrum splitting for the two-dimensional Fibonacci quasilattices in the framework of single-electron tight-binding on-site model. Analytic results show that there are only six kinds of clusters and the electronic energy band consists of nine subbands.     

Electronic properties of Fibonacci and random Si-Ge chains

In this paper we address a theoretical calculation of the electronic spectra of an Si-Ge atomic chain that is arranged in a Fibonacci quasi-periodic sequence, by using a semi-empirical quantum method based on the Hückel extended model. We apply the Fibonacci substitutional sequences in the atomic building blocks A(Si) and B(Ge) through the inflation rule or a recursion relation. In our ab initio calculations we use only a single point, which is sufficient for considering all the orbitals and charge distribution across the entire system. Although the calculations presented here are more complete than the models adopted in the literature which take into account the electronic interaction only up to the second and third neighbors, an interesting property remains in their electronic spectra: the fractality (which is the main signature of this kind of system). We discuss this fractality of the spectra and we compare them with the random arrangement of the Si-Ge atomic chain, and with previous results based on the tight-binding approximation of the Schr?dinger equation considering up to the nearest neighbor.     

The properties of one-dimensional quasiperiodic lattice's phonon spectrum

A numerical method with renormalization group transformation is used to study the scaling properties of phonon spectrum and its relevant state of one-dimensional quasiperiodic lattice which is constructed by reduced map. We find that the phonon spectrum at finite gaps' edges in the binary chain Fibonacci model is a Cantor-like set spectrum. The spectrum is singularly continuous and the state is a critical state.     

Continuous-distribution puddle model for conduction in trilayer graphene

Influence of the weak electric field on the electronic structure of the Fibonacci superlattice is considered. The electric field produces a nonlinear dynamics of the energy spectrum of the aperiodic superlattice. Mechanism of the nonlinearity is explained in terms of energy levels anticrossings. The multifractal formalism is applied to investigate the effect of weak electric field on the statistical properties of electronic eigenfunctions. It is shown that the applied electric field does not remove the multifractal character of the electronic eigenfunctions, and that the singularity spectrum remains non-parabolic, however with a modified shape. Changes of the distances between energy levels of neighbouring eigenstates lead to the changes of the inverse participation ratio of the corresponding eigenfunctions in the weak electric field. It is demonstrated, that the local minima of the inverse participation ratio in the vicinity of the anticrossings correspond to discontinuity of the first derivative of the difference between marginal values of the singularity strength. Analysis of the generalized dimension as a function of the electric field shows that the electric field correlates spatial fluctuations of the neighbouring electronic eigenfunction amplitudes in the vicinity of anticrossings, and the nonlinear character of the scaling exponent confirms multifractality of the corresponding electronic eigenfunctions.     

Ballistic phonon transport through a Fibonacci array of acoustic nanocavities in a narrow constriction

We investigate the ballistic phonon transport through a Fibonacci array of acoustic nanocavities in a narrow constriction of a semiconductor nanowire at low temperatures. It is found that the transmission spectrum of such a system consists of quasiband gaps and narrow resonances caused by the coupling of phonon waves. Both phonon transmission and thermal conductance exhibit the similarity due to the Fibonacci sequence structure. The similarity is sensitive to the number n and parameters of nanocavities. The results are compared with those in a periodic acoustic nanocavities.