spin-Peierls系统低能量激发谱的理论研究

用玻色化技术和量子自洽方法研究了spin-Peierls系统的低能量激发谱,计算了二聚化相的基态、单粒子激发态和双粒子束缚态的能量、阻挫对其低能量行为的影响及其各自的自旋-自旋关联函数.结果表明,随着阻挫的增大,spin-Peierls系统中的基态能会逐渐减小,单粒子激发态能隙和双粒子束缚态能隙却会增大.双粒子束缚态和基态的关联函数具有类似的短程关联,而单粒子激发态的关联函数具有长程关联.因此导出,单粒子激发态为自旋三重态,双粒子束缚态与基态类似为自旋单态,它存在于双粒子连续激发态的下边.该结果与Ain等 关键词： spin-Peierls系统 束缚态 关联函数     

稀土和锕系化合物中重费密子行为

本文采用周期Anderson哈密顿量研究了稀土和锕系化合物中的重费密子行为。对f电子间库仑关联项做了平均场近似并引入自能项反映多体作用的效应。对自能项采用了单格位近似,在准粒子表象中讨论了系统的性质,通过对f电子平均占据数的自洽计算,得到了准粒子有效质量,讨论了形成重费密子的条件,以及相应的磁性的变化,并做了数值计算。所得结果与最近的实验进行了比较。 关键词：     

多元无序合金相干势近似的图形分析

本文将处理二元无序合金电子性质的平均单粒子和双粒子格林函数的图形分析推广到多元无序合金。在单格点近似下,如果我们自洽地处理累积量中的多次占有修正,则从图形分析得到的平均单粒子和双粒子格林函数与相干势近似的结果相一致。 关键词：     

Dicke模型的量子混沌和单粒子相干动力学特性

量子化的Dicke模型在非旋波近似条件下表现为量子混沌动力学特征.利用单粒子一阶时间关联函数,通过数值计算详细考察了Dicke模型中单粒子相干动力学特性.结果表明:当初始相干态处在混沌区域时,一阶时间关联函数曲线衰减较快,而当初始相干态处在规则区域时,一阶时间关联函数曲线衰减较慢,单粒子相干动力学对初态具有较强的敏感性,经典混沌抑制量子相干.考察单粒子相干动力学在相空间的平均演化性质,得到一种较好的量子经典对应关系.最后研究了相空间单粒子相干的整体动力学性质,更好地揭示了相空间的混沌和规则结构.     

纳米量级超导Al粒子在磁场中的Zeeman分裂

用随机矩阵理论对BCS理论中的自洽方程进行修正.由此得到的新自洽方程能合理地描述纳米量级Al粒子的超导电性.更进一步论证在外磁场作用下,s>0态由于Zeeman效应得出了实验中已观测到的超导增强效应. 关键词： 纳米粒子 超导电性 Zeeman分裂     

激发态的相关基函数理论

本文根据相关基函数理论建立了电子相互作用体系的激发态理论。在Chakravarty-Woo方程的基础上,利用泛函展开和卷积近似得到了单粒子激发而引起的电子密度分布和关联函数变化的自洽方程。由多体理论的激发能的定义出发,求得了导电聚合物(考虑了电子相互作用)的能隙公式,在已知的参数下,给出了与实验相符的结果。 关键词：     

致密天体中电子气体对原子核结构的影响

运用相对论平均场理论结合Wigner-Seitz近似,研究了致密物质中电子气体对⁵⁶Fe和¹²⁰Sr结构的影响,对关联的处理采用Bardeen-Cooper-Schrieffer方法.结果表明电子气体对单粒子能级、核子密度分布、核子分布均方根半径、原子核均方根半径等性质都有影响,并且对质子的影响大于对中子的影响. 关键词： 相对论平均场理论 Wigner-Seitz近似 单粒子能级 均方根半径     

p型金属氧化物半导体场效应晶体管界面态的积累对单粒子电荷共享收集的影响

由于负偏置温度不稳定性和热载流子注入,p型金属氧化物半导体场效应晶体管(pMOSFET)将在工作中不断退化,而其SiO₂/Si界面处界面态的积累是导致其退化的主要原因之一. 采用三维器件数值模拟方法,基于130 nm体硅工艺,研究了界面态的积累对相邻pMOSFET之间单粒子电荷共享收集的影响. 研究发现,随着pMOSFET SiO₂/Si界面处界面态的积累,相邻pMOSFET漏端的单粒子电荷共享收集量均减少. 还研究了界面态的积累对相邻反相器中单粒子电荷共享收集 关键词： 负偏置温度不稳定性 电荷共享收集 双极放大效应 单粒子多瞬态     

双Λ超核同位旋标量巨共振性质的相对论研究

基于相对论平均场理论(RMF),采用TM1以及有效超子-核子和超子-超子相互作用,首先研究了¹⁶O和_ΛΛ¹⁸O的单粒子能级受超子的影响情况,发现超子的加入使得核子能级能量降低.其次基于相对论无规位相近似方法 (RRPA),自洽地计算了¹⁶O和_ΛΛ¹⁸O同位旋标量巨单极和四极共振态.发现相比于¹⁶O各巨共振的响应函数,超核的响应函数会发生改变.研究表明:这种改变主要来自于超子的加入导致的核子单粒子能级的改变,以及超子粒子-空穴组态跃迁的贡献,而超子-超子剩余相互作用对单极和四极共振在低能区的响应函数的影响比较小,特别对高能区的响应函数基本没有影响.     

无序合金中相干势近似的另一种推导——紧束缚模型

本文用Matsubara和Toyozawa的locator展开方法重新推导单粒子和双粒子格林函数的相干势近似(CPA)方程,文中不采用对累积量做自洽处理的方法来考虑原子之间的体积排斥效应,而采用Yonezawa早先提出的一种图形法,本文的重点是提出一个可以用来生成单格点图形自洽方程的系统方法,并用在处理双粒子平均格林函数上,这种处理方法可以推广到处理包括液态金属或非晶态金属等具有短程序系统电导率的CPA方程。 关键词：     

A self-consistent mean field calculation of the phenomenological coefficients in a multicomponent alloy with high jump frequency ratios

We present an improvement of the self-consistent mean field (SCMF) approximation of the L _ij which extends its applications to alloys presenting high jump frequency ratios. The theory uses a vacancy–atom exchange model which depends on temperature and local composition through thermodynamic and kinetic parameters. Kinetic correlations due to the vacancy mechanism are represented by a time-dependent effective Hamiltonian. In the case of high jump frequency ratios it is shown that long return paths of the vacancy need to be considered, which is shown to be equivalent to introducing many-body long-range effective interactions. We compare this theory to existing formalisms and Monte Carlo simulations for systems both without and with atomic interactions.     

Quantum correlations in rotating nuclei

Using the Hamiltonian that consists of the separable quadrupole + pairing forces and the cranking term, we analyze the correlations associated with shape, orientation, and particle-number fluctuations in rotating nuclei. Quantum fluctuations around mean field solutions are treated in the random phase approximation (RPA), with special emphasis on the restoration of rotational symmetry and particle number conservation. The mean field calculations have been made within the self-consistent cranking model. The effect of the RPA correlation energy for the moment of inertia is studied with the integral representation method proposed.     

The electronic structure of modulation-doped In0.53Ga0.47As/n-In0.52Al0.48As heterostructure

Summary The subband structure of modulation-doped InGaAs/InAlAs heterostructures is calculated in a variational self-consistent manner. The dependence on various device parameters is examined. The many-body exchange correlation effects are taken into account.     

A realistic model of superfluidity in the neutron star inner crust

A semi-microscopic self-consistent quantum approach developed recently to describe the inner-crust structure of neutron stars within the Wigner-Seitz (WS) method with the explicit inclusion of neutron and proton pairing correlations is further developed. In this approach, the generalized energy functional is used which contains the anomalous term describing the pairing. It is constructed by matching the realistic phenomenological functional by Fayans et al. for describing the nuclear-type cluster in the center of the WS cell with the one calculated microscopically for neutron matter. Previously, the anomalous part of the latter was calculated within the BCS approximation. In this work corrections to the BCS theory which are known from the many-body theory of pairing in neutron matter are included into the energy functional in an approximate way. These modifications have a sizable influence on the equilibrium configuration of the inner crust, i.e. on the proton charge Z and the radius R _c of the WS cell. The effects are quite significant in the region where the neutron pairing gap is larger.     

The dependence of electronic transport on compressive deformation of C60 molecule

The dependence of electronic transport on compressive deformation of C₆₀ molecule is studied theoretically in this work. Brenner's “second generation” empirical potential is used to describe the many-body short-range interatomic interactions for C₆₀ in the molecular dynamics simulations. Our results demonstrate that C₆₀ can be compressed up to a strain ε=0.31 before collapsing. Electronic transport under an applied bias is calculated by using a self-consistent field approach coupled with non-equilibrium Green's function (NEGF) formalism. The transmission probability, conductance gap, and conductance spectrum are found to be sensitive to the compression. The peak value of conductance decreases with the increase of strain until the C₆₀ is compressed up to a strain ε=0.31.     

Dynamical correlations in the one-dimensional electron gas with short-range interactions

We study the dynamical correlation effects in a one-dimensional Fermion gas with repulsive delta-function interaction within the quantum version of the self-consistent field approximation of Singwi, Tosi, Land, and Sj?lander [Phys. Rev. 176, 589 (1968)]. The dynamic correlation effects are described by a frequency dependent local-field correction . There is a corresponding local-field factor for the spin-density correlations. We investigate the structure factors, spin-dependent pair-correlation functions, the frequency dependences of and , and the plasmon dispersion relation within this formalism. We compare our results with other theoretical approaches, in particular the static version of the self-consistent field approximation to highlight the importance of dynamical correlations. Received 11 December 1998 and Received in final form 25 April 1999     

Impact of exchange-correlation effects on the IV characteristics of a molecular junction

The role of exchange-correlation effects in nonequilibrium quantum transport through molecular junctions is assessed by analyzing the IV curve of a generic two-level model using self-consistent many-body perturbation theory (second Born and GW approximations) on the Keldysh contour. It is demonstrated how the variation of the molecule's energy levels with the bias voltage can produce anomalous peaks in the dI/dV curve. This effect is suppressed by electronic self-interactions and is therefore underestimated in standard transport calculations based on density functional theory. Inclusion of dynamic correlations introduces quasiparticle (QP) scattering which in turn broadens the molecular resonances. The broadening increases strongly with bias and can have a large impact on the calculated IV characteristic.     

Dynamics of Many-Body Correlation Green's Functions Ⅲ Truncation with Respect to Crder

All of the main non-perturbative results in the standard Green's function theory are obtained naturally and explicitly from the set of dynamic equations of the many-body correlation Green's functions by means of truncation up to lower correlations.The two-body correlation Green's function dynamics includes both ladder diagrams for short-range correlations and ring diagrams for long-range correlations in a unified way.     

Electron correlations and many-body techniques in magnetism

Recent progress in the theory of magnetism and electron correlations is reviewed to clarify the theories developed in the last decade and their mutual relations. A historical development of the theory of magnetism is outlined, and the dynamical coherent potential approximation (CPA) which completely takes account of the dynamical spin and charge fluctuations within the single-site approximation is introduced. Both the dynamical effects on various magnetic properties and the many-body band structure are shown to be explained on the same footing. It is shown that the dynamical CPA is equivalent to the other single-site theories of strongly correlated electrons: the many-body CPA, the dynamical mean-field theory (DMFT), and the projection operator method CPA (PM-CPA). These theories are elucidated with use of a common concept of effective medium or coherent potential. The effects of orbital degeneracy and the realistic calculation scheme are discussed with an emphasis on Hund’s rule coupling. Non-local theories of magnetism and electron correlations which go beyond the single-site approximation are presented. They include the molecular dynamics approach to the magnetic short range order, the dynamical cluster methods as a direct extension of the DMFT, and the self-consistent projection operator approach as an extension of the PM-CPA with use of the incremental cluster expansion. The current problems of their approaches and their future perspective are discussed.     

Self-Consistent Calculations of the Quadrupole Moments of the Lowest 3<Superscript>–</Superscript> States in Sn and Pb Isotopes

self-consistent approach to anharmonic effects based on the quantum many-body theory is for the first time used to calculate the quadrupole moments of the lowest 3^– states in Sn and Pb isotopes, including the ¹⁰⁰Sn, ¹³²Sn, and ²⁰⁸Pb doubly magic ones. The consistency between the mean nuclear field and the effective interaction is maintained using the energy-density-functional method with known parameters of the Fayans functional. Thereby, the quadrupole moments of the lowest 3^– states of isotopes with nucleon pairing are reliably predicted, and the existing data for the ²⁰⁸Pb isotope are reproduced. It has been shown that the new three-quasiparticle correlations are responsible for slightly more than half of the observed effect and the remaining part is due to the quadrupole polarizability of the nucleus.