一维强关联系统的Peierls相变温度与Hubbard模型参数的关系

在一维强关联电子系统中 ,用一维大UHubbard Peierls哈密顿量去讨论它的Peierls相变 ,其中用RPA求电子自能修正 ,发现这样的系统能引起一个反铁磁自旋波和声子相互作用而引起的二聚化相变 ,而且相变温度随掺杂参数δ的增加而降低 .这种处理方法在δt≥J的区域内有效 .

韧脆转变区16MnR钢断裂韧性变化规律研究——断裂韧性双峰的PEIERLS机制

用材料变形的热激活机制研究了 16MnR钢断裂韧性在韧脆转变区随温度的变化规律 ,通过对Peierls能垒双峰模型的分析计算 ,得出了Peierls能垒形状因子α =9时 16MnR钢断裂韧性J积分随温度的变化规律 ,并与 16MnR钢低温断裂韧性的试验结果进行了比较。结果表明 :韧脆转变区 16MnR钢断裂韧性双峰的出现是Peierls机制的作用 。

APPLICATION OF PARAMETRIC DERIVATION METHOD TO THE CALCULATION OF PEIERLS ENERGY AND PEIERLS STRESS IN LATTICE THEORY

Applying the parametric derivation method, Peierls energy and Peierls stress are calculated with a non-sinusoidal force law in the lattice theory, while the results obtained by the power-series expansion according to sinusoidal law can be deduced as a limiting case of non- sinusoidal law. The simplified expressions of Peierls energy and Peierls stress are obtained for the limit of wide and narrow. Peierls energy and Peierls stress decrease monotonically with the factor of modification of force law. Present results can be used expediently for prediction of the correct order of magnitude of Peierls stress for materials.

二维三角晶格的Peierls相变前后的声子色散曲线的研究

利用晶格动力学理论计算了二维三角晶格的Peierls相变前后的声子能谱。并且在第一布里渊区绘制了主要的对称点、线上的声子色散曲线。通过对Peierls相变前后的声子能谱比较可知 ,随其对称性降低 ,声子能谱的简并度被破缺。二维三角晶格的Peierls相变前只有两支声频支声子能谱 ,Peierls相变后有两支声频支声子能谱与两支光频支声子能谱 ,并且声频支声子能谱及光频支声子能谱不相交 ,两支光频支声子沿ky

掺杂蓝青铜的Peierls相变及非线性电输运性质

对钾钼蓝青铜 Ｋ０．３ Ｍｏ Ｏ３ 及其 Ｎａ 离子掺杂单晶 Ｋ０．３－ ｘ Ｎａｘ Ｍｏ Ｏ３ （ｘ ＝ ０．０２， ０．０５，０．１０）系列的 Ｐｅｉｅｒｌｓ 相变及７７ Ｋ 非线性电输运性质进行了系统研究发现 Ｎａ 离子掺杂对 Ｋ０．３ Ｍｏ Ｏ３ 单晶的 Ｐｅｉｅｒｌｓ 相变温度无明显改变，本文认为这是由于 Ｎａ 离子所起的两种相反作用的结果； Ｎａ 离子掺杂使样品的半导体能隙和第一阈值电场均明显增大，用钉扎理论对后者给予了定性解释；非线性电荷密度波电流 Ｉ Ｃ Ｄ Ｗ 与外场间满足指数关系： Ｉ Ｃ Ｄ Ｗ∝（ Ｖ／ Ｖ Ｔ － １）α，其中α≈３／２，并随 Ｎａ

电子-电子相互作用对Peierls相变的影响

研究短程强电子关联对Peierls相变的影响 .研究结果表明 ,短程强库仑作用对Peierls相变的影响与电子填充有关 .证明了电子单占据条件使费米面的态密度 ρ(εF)在n =1时奇异 ,此奇异性增强系统的二聚化 .此外 ,研究表明 ,增大最近邻电子 -电子相互作用V 将显著压低半满附近的Peierls相变温度Tp 以及增高n≈ 1/ 2附近的Peierls相变温度Tp;对n =1/ 2填充带 ,增大V将增进系统四聚化 .

铁磁自旋波对介观环中持续电流的影响Ⅱ．Peierls失稳中magnon的作用

研究在Ｔｅｘｔｕｒｅ结构中自旋波的量子涨落（ｍａｇｎｏｎ）对具有Ｐｅｉｅｒｌｓ失稳性的介观环持续电流的影响。

Peierls框架与裂纹尖端位错行为

本文在Peieris框架下对裂纹尖端位错成核与发射问题进行了严格的数学分析。在修正Rice设想的基础上,建立了一组新的控制方程。应力场与位错密度场分别表示成第一类与第二类切比雪夫多项式的级数。相应的张开位移与滑错位移可以用三角级数表示。通过离散的方法,控制方程转化为一组非线性代数方程。用Newton—Raphson方法求解这组方程,得到远场为纯剪、纯拉及两者复合情况下的解答。计算结果清楚地揭示了裂纹尖端位错成核与发射过程。

二维三角晶格的Peierls相变前后的声子色散曲面的研究

利用晶格动力学理论计算了二维三角晶格的Peierls相变前后的声子能谱。并且在第一布里渊区绘制了声子色散曲面。通过对Peierls相变前后的声子能谱比较可知 ,随其对称性降低 ,声子能谱的简并度被破缺。二维三角晶格的Peierls相变前只有两支声频支声子能谱 ,Peierls相变后有两支声频支声子能谱与两支光频支声子能谱 ,并且声频支声子能谱与光频支声子能谱不相交 ,两支光频支声子沿ky 轴平缓地变化。

Peierls Structural Transition in Q1D Organic Crystals of TTT<SUB>2</SUB>I<SUB>3</SUB>for Different Values of Carrier Concentration

The Peierls structural transition in the TTT2I3 (tetrathiotetracene-iodide) crystal, for different values of carrier concentration is studied in 3D approximation. A crystal physical model is applied that considers two of the most important hole-phonon interactions. The first interaction describes the deformation potential and the second one is of polaron type. In the presented physical model, the interaction of carriers with the structural defects is taken into account. This is crucial for the explanation of the transition. The renormalized phonon spectrum is calculated in the random phase approximation for different temperatures applying the method of Green functions. The renormalized phonon frequencies for different temperatures are presented in two cases. In the first case the interaction between TTT chains is neglected. In the second one, this interaction is taken into account. Computer simulations for the 3D physical model of the TTT2I3 crystal are performed for different values of dimensionless Fermi momentum kF, that is determined by variation of carrier concentration. It is shown that the transition is of Peierls type and strongly depends on iodine concentration. Finally, the Peierls critical temperature was determined.

Peierls基态的量子涨落效应

介绍了一维电-声相互作用体系中Peierls二聚化基态的量子晶格涨落效应的近期研究进展。在简略评述国内外相关工作的基础上,给出采用泛函积分方法在单圈图近似下获得的量子晶格涨落对基态二聚化的影响。对一维分子晶体Holstein模型,证明量子涨落会破坏Peierls二聚化,产生从二聚化的电荷密度波到Luttinger金属相的相变。这一结果纠正了前人的错误,并已得到同行的证实。对描写共轭高分子的Su-Schrieffer-Heeger模型,给出了在Gross-Neveu极限下,弱电声作用体系的零动量光学声子频率为零;非简并高分子的量子涨落减少;链间耦合部分抑制量子涨落,从而使得任何耦合常数和声子频率的体系量子涨落均不会破坏Peierls二聚化。

An improvement of the Peierls equation by taking into account the lattice effects

An improvement of the Peierls equation has been made by including the lattice effects. By using the non-trivially gluing mechanism for the simple cubic lattice, in which atoms interact with its first and second nearest neighbours through a central force, the dislocation equation has been derived rigorously for the isotropic case. In the slowly varying approximation, the Peierls equation with the improvement by including the lattice effects has been obtained explicitly. The new equation can be used to substitute for the old one in theoretical investigations of dislocations, The major change of the predicted dislocation structure is in the core region. The width of the dislocation given by using the new equation is about three times that given by the classical Peierls-Nabarro theory for the simple cubic lattice.

Dislocation energy and calculation from Peierls stress： a rigorous the lattice theory

In the classical Peierls-Nabarro （P-N） theory of dislocation, there is a long-standing contradiction that the stable configuration of dislocation has maximum energy rather than minimum energy. In this paper, the dislocation energy is calculated rigorously in the context of the full lattice theory. It is found that besides the misfit energy considered in the classical P-N theory, there is an extra elastic strain energy that is also associated with the discreteness of lattice. The contradiction can be automatically removed provided that the elastic strain energy associated with the discreteness is taken into account. This elastic strain energy is very important because its magnitude is larger than the misfit energy, its sign is opposite to the misfit energy. Since the elastic strain energy and misfit energy associated with discreteness cancel each other, and the width of dislocation becomes wide in the lattice theory, the Peierls energy, which measures the height of the effective potential barrier, becomes much smaller than that given in the classical P-N theory. The results calculated here agree with experimental data. Furthermore, based on the results obtained, a useful formula of the Peierls stress is proposed to fully include the discreteness effects.

轨道诱导Peierls相变材料MgTi_2O_4的电子自旋共振研究

用变温电子自旋共振手段(Electron Spin Resonance,ESR),对轨道诱导Peierls相变MgTi_2O_4体系进行了研究.研究发现,轨道诱导Peierls相变所伴随的自旋二聚相变对ESR谱产生了影响.在相变温度以上,MgTi_2O_4的磁性为顺磁行为.而在相变温度以下,ESR谱显示MgTi_2O_4的磁性偏离了顺磁行为.对ESR谱线的参数拟合结果显示,MgTi_2O_4在发生轨道诱导Peierls相变时,自旋耦合作用逐渐增强.这说明:自旋耦合作用的增强很有可能是导致相变的一个重要的因素.

准一维系统中的Peierls畸变

Ｃｎ聚合物群（ｐｏｌｙＣｎｇｒｏｕｐ）是一类简单而有代表性的准一维共轭聚合物，作者用一种统一的方法分析了这一整个序列．结果发现，由于键间耦合所产生的高维效应，准一维系统中Ｐｅｉｅｒｌｓ畸变并非不可避免．在这一意义上来说，Ｌｉｔｌｅ关于高温有机超导的设想是有可能实现的．

Quantum Mechanical Tunneling of Dislocations: Quantization and Depinning from Peierls Barrier

Theories of Mott and Weertmann pertaining to quantum mechanical tunneling of dislocations from Peierls barrier in cubic crystals are revisited. Their mathematical calculations about logarithmic creep rate and lattice vibrations as a manifestation of Debye temperature for quantized thermal energy are found correct but they can not ascertain to choose the mass of phonon or “quanta” of lattice vibrations. The quantum mechanical yielding in metals at relatively low temperatures, where Debye temperatures operate, is resolved and the mathematical formulas are presented. The crystal plasticity is studied with stress relaxation curves instead of logarithmic creep rate. With creep rate formulas of Mott and Weertmann, a new formula based on logarithmic profile of stress relaxation curves is proposed which suggests simultaneous quantization of dislocations with their stress, i.e., and depinning of dislocations, i.e., , where is quantum action, σ is the stress, N is the number of dislocations, A is the area and t is the time. The two different interpretations of “quantum length of Peierls barrier”, one based on curvature of space, i.e., yields quantization of Burgers vector and the other based on the curvature of time, i.e., yields depinning of dislocations from Peierls barrier in cubic crystals, are presented. , i.e., the unitary operator on shear modulus yields the variations in the curvature of time due to which simultaneous quantization, and depinning of dislocations occur from Peierls barrier in cubic crystals.

Phonons near Peierls Structural Transition in Quasi-One-Dimensional Organic Crystals of TTF-TCNQ

The Peierls structural transition in quasi-one-dimensional organic crystals of TTF-TCNQ is investigated in the frame of a more complete physical model. The two most important electron-phonon interaction mechanisms are taken into account simultaneously. One is similar of that of deformation potential and the other is of polaron type. For simplicity, the 2D crystal model is considered. The renormalized phonon spectrum and the phonon polarization operator are calculated in the random phase approximation for different temperatures. The effects of interchain interaction on renormalized acoustic phonons and on the Peierls critical temperature are analyzed.

Influence of Strong Electron-Electron Interaction on the Peierls Transition

The influence of short-ranged Coulomb repulsion of strongly correlated electrons on the Peierls transition for a quasi-one-dimensional system is investigated.It shows that the influence varies with the band filling and proves that the condition of single-occupation leads to a singularity on the density of states at half-filling which enhances dimerization.It also shows that dimerization is suppressed by the increase of U in the region of large-U and proves that increasing nearest-neighbor interaction V will suppress the Peierls transition temperature at half-filling,and strongly enhance it for band-filling at n≈1/4,which means the enhancement of tetramer-ization for a quarter-filled band.

含时Peierls方程的呼吸子近似解

呼吸子是一种广泛存在于非线性模型中的重要非线性振动模.本文给出了含时Peierls方程的近似呼吸子解,并且通过数值方法验证了呼吸子解的正确性.结果表明了动力学Peierls方程也存在呼吸子解,呼吸子可以看作是位错和反位错的束缚态.

Peierls stress for <110>{001} mixed dislocation in SrTiO_3 within framework of constrained path approximation

The core structure of （110）{001} mixed disloca- tion in perovskite SrTiO3 is investigated with the modified two-dimensional Peierls-Nabarro dislocation equation con- sidering the discreteness effect of crystals. The results show that the core structure of mixed dislocation is independent of the unstable energy in the （100） direction, but closely related to the unstable energy in the （110） direction which is the direction of total Burgers vector of mixed dislocation. Furthermore, the ratio of edge displacement to screw one nearly equals to the tangent of dislocation angle for differ- ent unstable energies in the （110） direction. Thus, the con- strained path approximation is effective for the （110）{001} mixed dislocation in SrTiO3 and two-dimensional equation can degenerate into one-dimensional equation that is only related to the dislocation angle. The Peierls stress for （110） {001 } dislocations can be expediently obtained with the one-dimensional equation and the predictive values for edge, mixed and screw dislocations are 0.17, 0.22 and 0.46 GPa, respectively.