Soliton-like excitations in the strong spin-phonon interaction

Soliton-like solutions are shown to exist in a one-dimensional chain of spins $\text{1}\text{2}$ strongly coupled to the lattice phonons. The features of these solutions are investigated and discussed.     

Magnetoelastic excitations and structural phase transitions in tetragonal paramagnets

The systematic discussion of the elastic and structural properties of the tetragonal paramagnetic model with the maximum value of the total angular momentumJ=1 in an external magnetic field along thez orx direction is given. The sound velocities of all the symmetry modes are calculated by using the standard perturbation theory and Green's function method. It is shown that only in the presence of the external field directed along thez-axis, for some values of this field and temperature one of the symmetry elastic constantsc ₄₄ orc _B becomes zero and the phase transition to monoclinic (triclinic) or volume change transition can occur.     

A surface wave dispersion relation for non-local media

Conditions are obtained for the existence of surface waves at the interface of vacuum and a semi-infinite non-local medium whose inverse dielectric function is assumed to be symmetric in spatial coordinate in the direction perpendicular to the interface. It is shown that these conditions reduce to those obtained by Maradudin in the appropriate limits: for the isotropic case; and for no retardation.     

A dispersion relation for gravitational radiation in a Schwarzschild background

A dispersion relation is derived for gravitational radiation emitted from an almost spherical object.     

APW dispersion relation for plasmon in metals

Following Ichikawa's technique we derived a dispersion relation for plasmons in metals using APW (Augmented Plane Wave) wave functions. The formula contained herein may be used to acquire information concerning the filling of the energy bands and so data needed in explaining electrical and magnetic properties of metals.     

A coupled-mode theory of heisenberg paramagnets

A new topographic method is presented using sound beams with frequencies at 24 GHz and 35 GHz for imaging crystal defects in nearly perfect dielectric crystals. Large crystals with dimensions up to 20×20×50 mm³ can be investigated. In this method the echo amplitude of longitudinal or transverse phonons is measured at low temperatures during a two-dimensional scan of a movable sound beam. The position dependent echo amplitude is presented as brightness-modulated image. The lateral resolution is limited by the effective diameter of the movable sound beam which is between 0.2 mm and 0.5 mm at present. The contrast pattern observed in natural quartz crystals can mainly be attributed to defects produced during growing time preferable at edges orr-faces andz-faces.     

Renormalized dispersion of elementary excitations in spinor polariton condensates

We analyse the polarization of spinor polariton condensates and corresponding dispersions of elementary excitations. We have considered the effects of magnetic field induced splitting in circular polarizations and residual splitting in linear polarizations in the ground state provided by the cavity asymmetry. We show that anisotropic polariton–polariton interactions fully compensate the Zeeman splitting in circular polarizations below the critical magnetic field, thus leading to the spin-Meissner effect for the polariton condensates. We also analyzed the effect of polariton–polariton interactions on the stability of the gap in linear polarizations characteristic for anisotropic microcavities. It was shown that in realistic systems this gap increases with concentration of the particles, thus contributing to the stability of the pinning of linear polarization of photoemission in semiconductor microcavities for pump intensities above the stimulation threshold.     

Local-field fluctuations in paramagnets

Equations are derived for the local-field fluctuations in a paramagnet. A comparison is made with the second moment and with the Lorentz local field.     

普遍色散关系下的热波长

指出目前教科书和文献所用的热波长概念仅适用于非相对论性系统，而本文引进了普遍热波长的概念。由此可使理想量子气体的热力学函数表示成统一的简洁形式，并进一步揭示了热波长的物理内涵。另外还导出玻色－爱因斯坦凝聚温度和费米温度间的普遍关系。     

Exciton dispersion and electronic excitations in hcp 4He

We present first measurements of the dispersion of excitons in solid helium, taken on a single hcp 4He crystal along the c axis. In agreement with studies on helium clusters, the major energy-loss peak can be interpreted as an intermediate molecular-type exciton, as we do not observe Wannier-like excitations. The measurements are in the (0 0 2) periodic zone, with the exciton energy dispersing along the c axis with a minimum at the gamma point. A calculated conduction band minimum at 31.0 eV above the valence band at gamma is supported by our data at energies above the exciton energy, leading to an exciton binding energy of 8.4 eV.     

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.     

A comparative study of the full dispersion relation, Compton dispersion relation, and Raman dispersion relation of a free-electron laser in helical wiggler and guiding magnetic fields

The full dispersion relation obtained for a free-electron laser in the presence of circularly polarized, periodic, static wiggler and guiding magnetic fields by the kinetic approach incorporating the particle trajectories is reduced to Compton and Raman regime approximations in the case of a tenuous electron beam. The temporal growth rate has been compared between the full dispersion relation and the Compton dispersion relation, as well as between the full dispersion relation and the Raman dispersion relation in the microwave region. The results show the maxima of growths in the full dispersion relation and the Compton dispersion relation, as well as the full dispersion relation and the Raman dispersion relation, are at the same locations, but the growth rates in both regimes are enhanced with respect to the full dispersion relation for the same plasma frequency and cavity parameters.     

Cubic dispersion relation for a relativistic backward-waveoscillator

The cubic approximation to the dispersion relation for a relativistic backward-wave oscillator is obtained, and the utility and limits of the approximation are presented. The approximation is obtained by Taylor series expansion of the wave admittance in the dispersion relation for the transverse-magnetic and free-streaming modes of a relativistic, thin, hollow, cylindrical electron beam moving along the axis of a disc-loaded waveguide in a strong axial magnetic field. The resulting cubic dispersion relation yields instability growth rates and frequencies which fall off beyond their maximum more sharply with increasing wavenumber than for the complete dispersion relation. The approximation is found to be quite good near the operating points of contemporary high-power relativistic backward-wave oscillators, namely, for relatively long wavelength and small ratio of Budker's parameter to the relativistic gamma factor of the beam     

On the spin-phonon interaction in anharmonic crystals

In this paper, a theory is developed for examining the influence of the spin-phonon interaction on the phonon dynamics in anharmonic crystals. In contrast to a harmonic approximation such an approach allows for comparing the role of the direct interaction between lattice vibrations with that of the indirect interaction via spins in the propagation and attenuation of sound as well as in the behaviour of thermodynamic quantities. Explicit expressions are derived for the phonon self-energy using successively higher approximations obtained from a cumulant expansion of the density of interparticle distances. It is shown that even in the harmonic approximation the two-spin correlation function and the four-spin correlation function enter into the expression of the generalized dynamical matrix in deviation from previous results. The modification of this harmonic dynamical matrix due to the renormalization of the harmonic phonons and due to phonon-phonon scattering processes is given employing a “weak coupling” approximation between the localized spins and the interparticle-distance density of the crystal. The resemblance of the present approach to an earlier microscopic treatment of electronic contributions to phonon dynamics in anharmonic crystals is pointed out.     

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建立了等离子体-绝缘管-真空结构的等离子体天线物理模型,推导了新的色散关系方程,通过几何诠释,给出了一种新的高精度快速收敛求解方法,计算机仿真验证了结论的正确性和有效性。利用算法研究了当电子密度按线性律减小时,圆柱等离子体天线的色散关系,并绘制了方向图。这些结果对等离子体天线的分析与设计具有重要的参考价值。     

Spin-phonon coupling in Van Vleck paramagnets

We investigate the effect of phonons on the phase transition of exchange induced Van Vleck paramagnets. We approximate the full crystalline-field level scheme of the magnetic ions by two singlet levels. It is shown that the coupling of the magnetic excitations to the phonons reduces appreciably the temperature dependence of the former near the ordering temperatureT _c . Special attention is focussed on Pr₃Tl and it is discussed to what extent the present mechanism might explain recent inelastic neutron-scattering data.