反铁磁体KCuF3中的孤立子能量

考虑磁-声子耦合作用和磁子间相互作用,采用双子格模型和相干态表示,研究了自旋S=1/2反铁磁体KCuF3的非线性集体激发特性,求出了孤立子的能量和质量,并比较了磁性孤立子和局域性磁子激发能量。结果表明在一维反铁磁体KCuF3中发现孤立子激发是可能。     

一维反铁磁分子晶体NENP中的孤立子激发

考虑到磁－声子耦合作用和磁子间的相互作用对非线性集体激发的贡献，我们采用Ｄｙｓｏｎ－Ｍａｌｅｅｖ变换和相干态表示，从一维反铁磁分子晶体ＮＥＮＰ的哈密顿得到了一个非线性Ｋｌｅｉｎ－Ｇｏｒｄｏｎ方程，研究了它的孤立子激发的性质，并求出了孤立子的能量。通过分析发现，只有在具有很强的各向异性反铁磁体中，才有可能观察到孤立子的激发。     

自旋波-声子耦合对反铁磁体红外吸收谱的影响

由于交换作用常数受到磁离子间距离变化的影响是不可忽略的,在磁有序物质中存在自旋波和声子的耦合作用。本文探讨了非金属反铁磁体中自旋波-声子耦合在红外吸收谱上可能有的表现,辐射场的电偶极矩作用在激发一个光频支声子的同时,通过自旋波-声子耦合又激发两个自旋波和一个声子,这就在晶格吸收谱的高频边缘以外形成附加吸收带。当反铁磁体的Néel点足够高,并且自施波态密度有尖锐的极大值时,附加吸收带就有超出晶格吸收边缘足够大的能量,且有明显的峯形,上述吸收峯就应在实验上观测到。把这一结果应用于NiO,解释了它的红外光谱中0.24电子伏的附加吸收峯,计算得到与实验相符合的吸收能量和吸收强度,并指出这一吸收机构只能在反铁磁体中而不能在铁磁体中发生。本文最后指出,Mizuno和Koide在企图解释同一现象的工作中,所探讨者相对于本文所考虑的跃迁机构,它只可能产生极其次要的贡献。     

序参量守恒的反铁磁分子晶体的非线性集体激发

采用双子格模型和相干态表示，考虑磁－声子耦合作用和磁子间的相互作用，研究了序参量守恒的一维反铁磁分子晶体ＣｅＡｓ在外磁场存在下的非线性集体激发特性，并求了孤立子能量、质量和自旋的空间组态，给出在一维序参量守恒的反铁磁分子晶体ＣｅＡｓ中出现的非线性磁子局域特性。     

序参量守恒的反铁磁分子晶体的非线性集团激发

采用双子格模型和相干态表示，考虑磁－声子耦合作用和磁子间的相互作用，研究了序参量守恒的一维反铁磁分子晶体ＣｅＡｓ在外磁场存在下的非线性集团激发特性，并求了孤立子能量，质量和自旋的空间组态，给出在一维序参量守恒的反铁磁分子晶体ＣｅＡｓ中出现的非线性磁子局域特性。     

弯曲应变下六角晶格量子反铁磁体的赝朗道能级

利用线性自旋波理论和量子蒙特卡罗方法研究了弯曲应变下六角晶格量子反铁磁体的赝朗道能级.通过线性自旋波理论,发现磁赝朗道能级出现在磁子能谱的高能端,其能级间距与能级指数的平方根成正比.线性自旋波理论和量子蒙特卡罗方法都显示,尺寸相同时随着应变强度的逐渐增加,局域磁化强度逐渐减弱,应变强度相同的条件下反铁磁序在y方向上连续减弱,因为上边界处的海森伯链解耦为孤立的垂直链,导致上边界附近的磁序被破坏.量子蒙特卡罗方法提供了更精确的反铁磁序演化:在特定应变强度下上边界处垂直关联不变,水平关联增加,从而影响磁化强度,使局域磁化在上边界处呈上翘趋势.研究结果有助于理解弯曲应变对自旋激发的影响,并可能在二维量子磁性材料实验中得以实现.     

酰胺Ⅰ与残基分子间不对称耦合作用下孤立子特性的变化

文内研究了酰胺Ⅰ振动与其前后胺基酸残基分子间不对称耦合对蛋白质分子链上所激发孤立子的能量、动量等特性的影响。结果表明，无论是亚声速孤立子还是超声速孤立子都能被激发，并且这种非对称耦合致使亚声速孤立子的波形振幅、能量及动量增大，孤立子的形成能降低     

低温下二维绝缘铁磁体的磁振子软化

在二维正方绝缘铁磁系统基础上建立了一个磁振子-声子相互作用模型.利用格林函数方法研 究了磁振子-声子相互作用下的二维绝缘铁磁体的磁振子谱, 计算了布里渊区的主要对称点 线上的磁振子色散曲线.发现在布里渊区边界区域磁振子谱的软化和磁振子谱线增宽最明显. 比较了纵向声子与横向声子对磁振子谱的软化与磁振子谱线增宽的影响，也讨论了各项参数 的变化对磁振子谱的软化与磁振子谱线增宽的影响. 关键词： 磁振子-声子相互作用 磁振子软化 铁磁体 磁振子谱线增宽     

CuCl2·2N（C5D5）中的孤子激发

采用双子格模型和相干态表示，考虑磁－声子耦合作用和磁子间的相互作用，研究了具有最近邻和次近邻相互作用的一维反铁磁分子晶体ＣｕＣｌ２·２Ｎ（Ｃ５Ｄ５）的非线性集体激发特性，分析了孤子的峰值、宽度、能量和有效质量的特点，结果表明ＣｕＣｌ２·２Ｎ（Ｃ５Ｄ５）中出现孤子激发是可能的。     

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.     

New properties of magnon density in uniaxial anisotropic ferromagnet on the background of spin wave

The N-soliton solutions of magnetization in uniaxial anisotropic ferromagnet on the background of spin wave are presented by using the effective Darboux transformation method. With the analytical solutions new properties of magnon density is studied in detail. On the ground state background the magnon density is constant for the spin wave solution and the magnetic soliton, respectively. However, on the spin wave background the magnon density possesses of temporal or spatial periodic oscillation. Moreover, the soliton solution possess the breather character in its propagation along the ferromagnet. These results show that during soliton propagation a periodic magnon exchange occurs between the magnetic soliton and the spin wave background.     

Quantum-statistical mechanics of non-linear excitations in the one-dimensional antiferromagnet

We study the quantum-statistical mechanics, at low temperatures, of a one-dimensional antiferromagnetic Heisenberg model with two anisotropies. In the weak-coupling limit, the temperature dependences of the soliton energy, and the soliton density are determined. At temperaturesT<m ₁ c (wherem ₁ c is the energy of the lowest energy magnon) the soliton density agrees with the classical statistical-mechanics results if the soliton energy in the classical theory is replaced by the renormalized one of the present theory.     

Solitons and magnons in Sine-Gordon like magnetic chains

We present theoretical results on the dynamic structure factors of both the classical Sine-Gordon chain and thexy-like ferromagnetic chain in a symmetry breaking magnetic field. We investigate the lowest order corrections to the noninteracting soliton/magnon picture and show that interference effects between solitons and magnons considerably reduce the intensity of the soliton induced central peak. We discuss the additional contribution of two magnon processes to the central peak and find that the combined strength is in agreement with numerical results. We calculate magnon intensities including quantum effects and find that the intensity depends strongly on temperature and wavevector. Quantitative results are given for the one-dimensional magnet CsNiF₃ and compared to neutron scattering data. The soliton induced line-width of the long wavelength magnon is also given.     

Exact soliton solution of spin chain with an external magnetic field in linear wave background

Employing a simple, straightforward Darboux transformation we construct exact N-soliton solution for anisotropic spin chain driven by an external magnetic field in linear wave background. As a special case the explicit one- and two-soliton solution dressed by the linear wave corresponding to magnon in quantum theory is obtained analytically and its property is discussed in detail. The dispersion law, effective soliton mass, and the energy of each soliton are investigated as well. Our result show that the stability criterion of soliton is related with anisotropic parameter and the amplitude of the linear wave.     

Stochastic motion of Sine-Gordon-solitons and the spin-correlation function of CsNiF3

The interaction of solitons and magnons (linear modes) of the Sine-Gordon equation is studied. The phase shift of the magnon in presence of a soliton gives rise to a shift of the position of the soliton, if magnon wave packets are considered. This leads to a stochastic part of the soliton motion in a gas of thermally activated magnons yielding an effective velocity and a diffusion constant. The influence of this effect on the solitonic part of the correlation function is discussed and compared with the recent experiment by Steiner and Kjems.     

Acoustic Solit on in One-Dimensional Ferromagnetic Systems

The local nonlinear excitation caused by the magnon-phonon interactions as an anisotropic source of nonlinearity is studied. The nonlinear equation for the Schrodinger probability amplitude of spin motion is given, and its soliton solutions are obtained in a weak coupling approximation. The existence conditions are discussed. It is shown that the soliton excitation energy can be less than a one-magnon state and a gap appears in the energy spectrum. The effect of the magnon-rnagnon interactions on the local acouitic soliton excitation is also discussed.     

光频支声子对二维Heisenberg铁磁系统磁激发的影响

在二维复式正方Heisenberg铁磁系统的基础上建立了磁振子-声子相互作用模型. 利用松原格林函数理论研究了系统的磁激发，计算了布里渊区的主要对称点线上的磁振子色散曲线，比较了光频支声子与声频支声子对系统磁激发的影响以及各项参数的变化对磁振子软化的影响. 发现光频支声子-磁振子耦合对磁振子软化起主要作用，尤其是纵向光频支声子对磁振子软化起更大的作用，并且非磁性离子的光频支声子对磁振子软化的作用比磁性离子的光频支声子对磁振子软化的作用更显著.     

Resonance THz spectroscopy in high magnetic fields

The employment of the high-magnetic-field resonance spectroscopy to probe magnetic excitations in the THz frequency range is reported. To illustrate the great potential of this technique in solid state physics, we present results of recent electron spin resonance studies of the quantum-tunneling effect in the single-molecule magnet Mn12tba and of the soliton–magnon crossover in Cu-PM, a spin-1/2 Heisenberg chain system with a staggered transverse field. Among others, we report on the successful use of the THz-range time-domain and free electron laser spectroscopy to study magnetic excitation spectra in pulsed magnetic fields.