Magnetic Properties of One-Dimensional Ferromagnetic Mixed-Spin Model within Tyablikov Decoupling Approximation

In this paper, we apply the two-time Green's function method, and provide a simple way to study the magnetic properties of one-dimensional spin-(S,s) Heisenberg ferromagnets. The magnetic susceptibility and correlation functions are obtained by using the Tyablikov decoupling approximation. Our results show that the magnetic susceptibility and correlation length are amonotonically decreasing function of temperature regardless of the mixed spins. It is found that in the case of S=s, our results of one-dimensional mixed-spin model is reduced to be those of the isotropic ferromagnetic Heisenberg chain in the whole temperature region. Our results for the susceptibility are in agreement with those obtained by other theoretical approaches.     

Cellular Model with Improved Decoupling Approximation in Random Nonlinear Composite

Cellular model with improved decoupling approximation is proposed to study the effective nonlinear response in random nonlinear granular materials. The results are compared with numerical simulations on random nonlinear resistor networks, a good agreement is obtained.     

二维磁性系统和准一维磁性纳米管的内能

采用量子统计理论的多体格林函数法计算二维单离子各向异性海森伯铁磁体、反铁磁体以及单壁铁磁纳米管的内能,对比铁磁体和反铁磁体的结果.在相同的参量下,反铁磁能量总是低于相应的铁磁能量(相变点除外).由于反铁磁能量随温度上升的速度较铁磁能量快,当温度升高到居里点T_C和奈尔点T_N时(T_C=T_N),铁磁能量和反铁磁能量相等.横向关联效应对系统内能的影响较大,不能忽略.     

Ferromagnetic Domain Wall and Spiral Ground States in One-Dimensional Deformed Flat-Band Hubbard Model

We construct a set of exact ground states with a localized ferromagnetic domain wall and an extended spiral structure in a quasi-one-dimensional deformed flat-band Hubbard model. In the case of quarter filling, we show the uniqueness of the ground state with a fixed magnetization. The ground states with these structures are degenerate with the all-spin-up and all-spin-down states. This property of the degeneracy is the same as the domain wall solutions in the XXZ Heisenberg–Ising model. We derive a useful recursion relation for the normalization of the domain wall ground state. Using this recursion relation, we discuss the convergence of the ground state expectation values of arbitrary local operators in the infinite-volume limit. In the ground state of the infinite-volume system, the translational symmetry is spontaneously broken by this structure. We prove that the cluster property holds for the domain wall ground state and excited states. We also estimate bounds of the ground state expectation values of several observables, such as one- and two-point functions of spin and electron number density.     

On Superconductivity State in Pure Graphene

We study theoretically the possibility of superconductivity state in pure graphene within the extended attractive Hubbard model. In the absence of disorder, when we use the local attractive interaction potential, U ≌ 5t, where t is hopping term, pure graphene can be in superconductivity state.     

Functional Integrals and Excitation Energy in Three-Band Hubbard Model

The normal and anomalous Green＇s functions of antiferromagnetie state in three-band Hubbard model are studied by using functional integrals and temperature Green＇s function method. The equations of energy spectrum are derived. In addition, excitation energy of Fermi fields are calculated under long wave approximation.     

外磁场对纳米管上Blume-Capel模型磁热性能的研究

利用有效场理论研究了纳米管上外磁场中Blume-Capel模型格点的磁化强度、磁化率、内能、比热和自由能,得到了系统格点的磁化强度、磁化率、内能、比热和自由能与外磁场和晶场的关系.结果表明:外磁场强度、交换相互作用和晶场强度等诸多因素相互竞争,使系统表现出比没有外磁场作用的Blume-Capel模型更为丰富的磁学特性;外磁场能够增大系统格点的磁化强度,导致系统的二级相变消失;负晶场作用系统时,系统会发生一级相变;晶场强度、外磁场强度不同时,系统的磁化率、内能、比热和自由能也呈现出复杂性.     

钴纳米结构光学性质的离散偶极近似分析

基于离散偶极近似理论,模拟分析了四种不同钴纳米结构的光学性质,具体讨论了钴单质半径、钴金合金材料的组分、钴金核壳结构中的内核大小及壳厚度、钴空心球的尺寸及空球壳厚度等参数对其消光光谱的影响。结果表明,半径50nm的钴颗粒水溶液消光效率最大,且散射强度优于吸收;中空钴球相比实心颗粒消光谱红移,内半径40nm、壳厚5nm的空心钴纳米结构在可见光区域的消光效率最高;半径50nm、钴金原子成分比值为1的合金颗粒在可见光区域具有较宽的散射光谱;随钴金核壳结构中核壳尺寸的增大,消光谱都由显示有两个峰位的波形演化为一个半高宽较大的波形,颗粒特性受核壳金属的共同作用。这些结果可以为其在太阳能领域等应用中的结构参数选择提供参考和借鉴。     

The Critical Properties of One—Dimensional Extended Hubbard Model

In the framework of nonperturbative quantum field theory,the critical phenomena of one-dimensional extended Hubbard model (EHM) at half-filling are discussed from weak to intermediate interactions.After the EHM being mapped into two decoupled sine-Gordon models,the ground state phase diagram of the system is derived in an explicit way.It is confirmed that the coexisting phases appear in different interaction regimes which cannot be found by conventional theoretical methods.The diagram shows that there are seven different phase regions in the ground state,which seems not to be the same as previous discussions,especially the boundary between the phase separation and condensed phase regions.The phase transition properties of the model between various phase regions are studied in detail.     

Gauge Invariance of a Time-Dependent Harmonic Oscillator in Magnetic Dipole Approximation

A manifestly gauge-invariant formulation of non-relativistic quantum mechanics is applied to the case of time-dependent harmonic oscillator in the magnetic dipole approximation. A general equation for obtaining gauge-invariant transition probability amplitudes is derived.     

外磁场作用下一维光子晶体的光传输特性

采用光学传输矩阵方法,研究了外磁场作用下一维光子晶体的光传输特性.在外磁场作用下,介质介电函数在回旋频率ω.附近受到强烈的调制,使组分材料的色散关系发生明显改变,导致光子晶体的能带发生变化,透射谱出现复杂结构.在光子带隙中出现窄通带,窄带中的光是局域的.这表明,在不改变光子晶体组分材料的条件下,可以通过改变外磁场的大小,调制光子晶体的能带及其光传输性质.     

The Physical Property of Susceptibility for One-Dimensional Ferrimagnetic Chain with Alternating Spins 1 and 1/2 in Finite Magnetic Field

We further calculate the dependence of xT on T in high magnetic fields,where X denotes susceptibility and T is temperature,using our previous research work - Green function‘s decoupling approximate approach,for the one-dimensional ferrimagnetic chain with alternating spins 1 and 1/2.We find a linear correlation in certain range of magnetic field between the temperature of xT maximum and the magnetic field.Moreover,we simply analyze its physical meaning by our approach.``     

High—Temperature Cutoff Approximation of the 3D kinetic Ising Model

A single-spin transition critical dynamics is used to investigate the three-dimensional kinetic Ising model on an anisotropic cubic lattice,We first derive the fundamental dynamical equations.and then linearize them by a cutoff approximation.We obtain the approximate solutions of the local magnetization and equal-time pair correlation function approximation.We obtain the approximate solutions of the local magnetization and equal-time pair correlation function in zero field.In which the axial-decoupling terms γ1γ2,γ2γ3and γ1γ3as higher infinitesimal quantity are ignored,where γα=tanh(2k0633)=tanh(2Jα/kβT）（α=1,2,3,)We think that it is reasonable as the temperature of the system is very high.The result of what we obtain in this paper can go back to the one-dimensional Glauber‘s theory as long as k2=k3=0.     

The Physical Property of Susceptibility for One-Dimensional Ferrimagnetic Chain with Alternating Spins 1 and 1/2 in Finite Magnetic Field

We further calculate the dependence of χT on T in high magnetic fields,where χ denotes susceptibility and T is temperature,using our previous research work - Green function's decoupling approximate approach,for the one-dimensional ferrimagnetic chain with alternating spins 1 and 1/2.We find a linear correlation in certain range of magnetic field between the temperature of χT maximum and the magnetic field.Moreover,we simply analyze its physical meaning by our approach.     

Strain effect on transport properties of hexagonal boron—nitride nanoribbons

<正>The transport properties of hexagonal boron-nitride nanoribbons under the uniaxial strain are investigated by the Green's function method.We find that the transport properties of armchair boron-nitride nanoribbon strongly depend on the strain.In particular,the features of the conductance steps such as position and width are significantly changed by strain.As a strong tensile strain is exerted on the nanoribbon,the highest conductance step disappears and subsequently a dip emerges instead.The energy band structure and the local current density of armchair boron-nitride nanoribbon under strain are calculated and analysed in detail to explain these characteristics.In addition,the effect of strain on the conductance of zigzag boron-nitride nanoribbon is weaker than that of armchair boron nitride nanoribbon.     

Critical Properties of a Generalized Planar Rotator Model

The critical properties of the planar rotator model with chiral Dzyaloshinsky-Moriya interaction are analyzed using a hybrid Monte Carlo method. Simulations on different lattices conform an observation that there is an XY-like Berezinskii-Kosterlitz-Thouless (BKT) phase transition in this model. The ground state and some thermodynamics properties are also discussed.     

硫化锌纳米管稳定性、电子性质和磁性质的比较研究

用第一性原理方法系统地研究硫化锌纳米管的稳定性、电子性质和掺杂磁性质.比较三种纳米管的稳定性.研究表明,六边形截面的双壁管的稳定性最高,相同截面的单壁管稳定性次之,而圆截面的之字形和扶手椅纳米管稳定性最低.电子能带结构计算表明它们都是直接带隙半导体.纳米管表面氢吸附后,六边形截面的单壁管转变为间接带隙半导体.研究了磁性原子掺杂六边形截面管的磁性质.发现掺杂纳米管的形成能比纯纳米管的形成能低,说明掺杂过程是一个放热反应.纳米管的总磁矩等于掺杂的磁性原子的磁矩.这些单掺杂纳米管在可调磁的新材料方面有潜在的应用价值.     

Effect of Logarithmic Mesonic Potential on Nucleon Magnetic Moments and Hedgehog Mass

The logarithmic mesonic potential is proposed for computing some nucleon properties. The logarithmic potential is based on some aspects of QCD. The field equations have been solved in mean-field approximation. Good results are obtained for the nucleon magnetic moment and the hedgehog mass in comparison with the Skyrmion model. In particular, nucleon properties are calculated for sigma and quark masses which are computed recently.     

推广的Thomas－Fermi方法中适用的新式核密度

给出一种适用于推广的Ｔｈｏｍａｓ－Ｆｅｒｍｉ方法（ＥＴＦ）的密度形式．取ＳｋＭ势参量，对几个球形核的基态性质进行了计算，结果优于通常采用的多参数密度形式．用期望值方法（ＥＶＭ）给出的基态能量能重现Ｈ—Ｆ的计算结果．     

三维频域格林函数的高效率计算方法

将高斯积分引入频域格林函数及其导数的数值计算,计算结果与已有文献进行对比,证明该方法在满足足够精度的基础上,使计算过程简化,减少分区,提高计算效率.