自旋1/2铁磁模型的相互作用淬灭

本文设想了一个相互作用淬灭后在t=0时刻开启的海森堡反铁磁模型,并对其进行了解析分析.在低温近似下,通过求解海森堡方程给出该系统随时间演化的自旋算符的解析形式.文中主要推算并讨论了自旋传播子,通过对传播子的讨论发现这个新体系的自旋波谱发生了变化.文末对此现象进行了讨论.     

双自旋系统中的量子失协问题研究

利用量子失协的几何度量方案研究了双自旋海森堡模型中的量子关联特性, 得到了一般情形下两量子态量子失协度的解析表达式, 讨论了量子位之间的耦合强度、温度和外加磁场强度等对量子关联大小的影响, 并给出了对应的量子关联调控方案. 此外还发现在低温下量子失协存在突变的现象. 结果表明, 在双自旋的海森堡模型体系下, 可以通过对系统参数(如温度、耦合强度、磁场强度等)的调节来实现对量子关联大小的有效调控, 这将会对在量子信息科学中精确控制量子失协和实现量子态的隐形传输以及量子逻辑门的设计提供一定的借鉴和指导意义.     

铁砷超导体比热特征的理论和实验比较研究

以海森堡相互作用模型为基础,系统分析了铁砷超导体自旋密度波的反铁磁表现形态,计算了长波近似条件下的内能和比热等理论值,比较讨论了与实验结果的符合情况及其相应意义,表明自旋密度波理论在较低温度下基本能够描述铁砷超导体的有关特征.详细分析讨论了电子和声子在不同低温区对比热的贡献,与实验结果进行了比较.     

不同方向外磁场下海森堡自旋链的热纠缠

研究了两量子比特的海森堡XXX自旋链分别处于x方向和y方向均匀外磁场时系统的纠缠特性,并用负度N来度量。得到纠缠度N的解析表达式,并在此基础上进行数值计算。仔细讨论了磁场B、温度T和自旋耦合系数J对纠缠度N的影响。结果表明：纠缠度N会随着磁场|B|和温度T的增大而减小,但会随着自旋耦合系数J的增大而增大。另外,增大的J还会使临界磁场|Bc|和临界温度Tth变大。所以,我们可以通过调节B、T和J来控制热纠缠,这对固态系统中通过构建和选择参数调整系统的纠缠度具有一定的作用和意义。研究还发现,加在x方向均匀外磁场和加在y方向均匀外磁场对两量子比特的海森堡XXX自旋链的作用效果是一样的。     

量子海森堡自旋玻璃的相图：各向异性和铁磁相互作用效应

应用静态的Ｒｅｐｌｉｃａ对称自旋玻璃理论，研究了具有Ｄｚｙａｌｏｓｈｉｎｓｋｉｉ－Ｍｏｒｉｙａ（ＤＭ）各向异性和铁磁相互作用的量子海森堡自旋玻璃模型，数值计算了自１／２自旋玻璃序参数及自旋自相互作用，并在温度－铁磁耦合强度平面内得到了相应的相图，最后对结果进行了讨论。     

含三体相互作用的海森堡自旋链纠缠研究

研究了含三体相互作用的海森堡自旋链的能级和相应本征态的纠缠情况,详细分析了含有三个粒子的海森堡自旋链的纠缠,发现所有的纠缠态都为W态。给出三粒子海森堡自旋链在温度为零时的基态纠缠,发现反铁磁自旋链的基态不随各向异性、耦合强度等参数发生变化,铁磁自旋链的基态纠缠随各向异性因子和三自旋耦合项而改变。讨论了三比特自旋链在低温时的热纠缠,给出纠缠度表达式及其随温度、各向异性因子和耦合强度的变化关系。     

三比特铁磁质海森堡自旋链模型的热纠缠

本文对带DM相互作用的铁磁质海森堡XXZ自旋链模型在磁场中的热纠缠进行了详细地计算和分析. 通过画图发现铁磁质模型的热纠缠远大于反铁磁质模型的热纠缠. 同时发现外磁场 ,耦合系数 和DM相互作用 都可以有效地控制纠缠和临界温度 . 该结论为实验上利用海森堡XXZ模型的纠缠特性进行隐形传态提供了很好的理论依据.     

铁磁/反铁磁双层薄膜中自旋波特性研究

本文在一维海森堡模型的基础上,采用界面参数化方法,研究了非周期性边界条件下,铁磁/反铁磁双层薄膜中自旋波低温激发问题.重点讨论了表面各项异性对薄膜中自旋波谱、色散关系的影响.结果表明:表面各向异性对铁磁层中自旋波谱影响较大,对色散关系影响甚微。     

三比特铁磁质海森堡自旋链模型的热纠缠

本文对带Dzyaloshinskii-Moriya(DM)相互作用的铁磁质海森堡XXZ自旋链模型在磁场中的热纠缠进行了详细地计算和分析.通过画图发现铁磁质模型的热纠缠远大于反铁磁质模型的热纠缠.同时发现外磁场B,耦合系数J_Z和DM相互作用D都可以有效地控制纠缠和临界温度T_C.该结论为实验上利用海森堡XXZ模型的纠缠特性进行隐形传态提供了很好的理论依据.     

有机器件电流自旋极化放大性质研究

基于自旋扩散漂移方程,考虑到电场的影响及有机半导体中特殊的载流子电荷自旋关系, 对一个简单的T型结构有机自旋器件模型进行了理论研究,得出了此有机器件的电流自旋 极化放大率表达式.研究表明,器件中极化子比率、电场和电流密度都会影响器件的电流 自旋极化放大率,通过调节此有机器件的电场和极化子比率可以获得较大的电流自旋 极化放大率.     

Spin-liquid state for two-dimensional Heisenberg antiferromagnets on a kagomé lattice

The magnetic properties of the spin liquid state of the antiferromagnetic Heisenberg model on the kagomé lattice are investigated within the self-consistent mean-field theory. The results show that the spin liquid ground-state energy per site is , which is in very good agreement with the best numerical estimates. The spin structure factor and spin susceptibility are also discussed. Received 1 December 1998 and Received in final form 12 April 1999     

Path Integral Approach of Quantum Heisenberg Planar Spin Glass Model in the Presencesof Random Field

A quantum version of the site-random Heisenberg planar XY model in a random field is presented in the boson representation. Like classical spherical model in the spin space, the model can be solved exactly within the coherent state path integral-representation. The phase diagram is obtained, and the effects of the randomness and quantum fluctuations on the onset of a spin glass phase are discussed.     

On the gauge equivalence of the Landau-Lifshitz and the nonlinear Schrödinger equations on symmetric spaces

The gauge equivalence between a generalized Heisenberg spin chain (G/H) in the classical and continuum limit and the nonlinear Schrödinger equation (NLSE), with special attention to noncompact groups, is established. It has been demonstrated that noncompact groups allow a richer spectrum of possible reductions of the Heisenberg system to the NLSE. Some specialities of the model with nontrivial boundary conditions are discussed. The gauge equivalence between single-axis anisotropic Landau-Lifshitz equations (LLE) and isotropic LLE is briefly discussed.     

Transport coefficients in Heisenberg paramagnets

The Heisenberg model is discussed in the paramagnetic region, using the method of moments in the spectral representation of spin correlation functions. We discuss the validity of Green's function decoupling approximations and derive expressions for the spin diffusion and thermal conductivity of a simple cubic lattice and linear chain. The results of the calculations are in qualitative agreement with previous work.     

Heisenberg XYZ Hamiltonian with integrable impurities

A Hamiltonian of the impurity model is constructed within the framework of the open boundary Heisenberg XYZ spin chain. This impurity model is exactly solvable and degenerates to the integrable XXZ impurity model in the triangular limit. This approach is the first to add the integrable impurities to the completely anisotropic Heisenberg spin model with open boundary conditions.     

一种等效于反铁磁海森伯混合自旋链的铁磁-反铁磁交替自旋链

利用严格对角化方法研究了一种自旋为1/2的铁磁-反铁磁交替自旋链的物理性质.计算了自旋关联函数、自旋z方向分量、自旋激发谱和磁化曲线等基本物理量,并将这些物理量和自旋为(1,1/2)的混合反铁磁自旋链对应的物理性质进行了比较.结果表明,当铁磁作用居于主导地位时,该模型的物理行为等效于混合自旋模型.因此,可以通过分析铁磁-反铁磁交替自旋链的物理性质研究混合自旋链的物理行为.     

Noncollinear spin reorientation transition in S?=?1 ferromagnetic thin films

An in-plane spin reorientation transition in thin ferromagnetic films is discussed in terms of the thermodynamics of inhomogeneous low-dimensional systems based on a Néel sublattices concept while using a spin 1 Heisenberg Hamiltonian. The model allows us to investigate in a straightforward manner the layer-dependent phenomena. In this context, we propose a model of noncollinear magnetization structure based on the appropriate distribution of the anisotropy parameters inside the Fe films on W(110). The spin reorientation transition originates at the Fe/W(110) interface and proceeds via noncollinear magnetization structure toward the surface with increasing film thickness in accordance with the experimental findings. The temperature-driven spin reorientation transition in freestanding Fe films and in Fe/W(110) systems is also discussed in detail.     

Zero field muon spin relaxation in simple magnets and spin glasses

A theory is developed for the calculation of zero field muon spin relaxation function for classical simple magnets (Ising, XY, and Heisenberg) in D(=1,2,3) dimensions. The results are different from the Kubo-Toyabe theory, except for Heisenberg system in three dimension. Relation between the relaxation function and random field distribution is dicussed and a new method of analysing experimental data is suggested and discussed in the context of spin glasses.     

不变本征算符法计算各向异性海森伯亚铁磁系统的自旋波能量

利用不变本征算符法计算了X-Y-Z模型各向异性海森伯亚铁磁系统的自旋波能量,并讨论了此系统特殊情形下的自旋波能量及不变本征算符法的优点与不足.