Hamiltonian description of barotropic Rossby waves

A transformation into the normal canonical variables is found in the beta-plane approximation for barotropic Rossby waves of an arbitrary amplitude. This transformation is used to derive a matrix of three-wave interaction and to find an expression for the fourth-order term in the interaction Hamiltonian, which describes the modulation instability of Rossby waves. An increment of this instability has been calculated and estimated numerically.     

Emergence of X-shaped spatiotemporal coherence in optical waves

Considering the problem of parametric nonlinear interaction, we report the experimental observation of electromagnetic waves characterized by an X-shaped spatiotemporal coherence; i.e., coherence is neither spatial nor temporal, but skewed along specific spatiotemporal trajectories. The application of the usual, purely spatial or temporal, measures of coherence would erroneously lead to the conclusion that the field is fully incoherent. Such hidden coherence has been identified owing to an innovative diagnostic technique based on simultaneous analysis of both the spatial and temporal spectra.     

Nonlinear electrostatic waves in a magnetized plasma

The modulational interaction of finite-amplitude high-frequency electrostatic waves propagating at an arbitrary angle to an external magnetic field with slow plasma motion is considered. A set of nonlinear evolution equations describing the interaction is obtained. New types of solitary waves propagating at near sonic speeds are found.     

Generation of flexural waves in plates by laser-initiated airborne shock waves

Results of the semi-analytical modelling of the interaction of laser-initiated airborne shock waves with an infinite horizontally positioned elastic plate are presented. The impact of the airborne shock waves on the plate is approximated by a cylindrically diverging surface force resulting from the pressure of the incident and reflected shock waves. This force is then represented in the wavenumber-frequency domain by means of Hankel and Fourier transforms that are carried out numerically so that the interaction problem can be solved using the Green’s function method. The resulting frequency spectra and time histories of generated flexural wave pulses are calculated for different values of laser pulse energy and for different heights of the laser beam focusing above the plate surface. The theoretical results obtained are compared with the results of laboratory measurements of the interaction of laser-generated acoustic shocks with a large plastic plate. The comparison shows reasonably good agreement between the semi-analytical predictions and data.     

Spin waves in cold gases with the spin-orbit interaction

A new type of spin waves that appear in cold paramagnetic gases owing to the spin-orbit interaction has been predicted. The Boltzmann gases of heavy atoms with a nonzero orbital angular momentum are considered. The dispersion relation of the spin waves is determined by the scattering amplitude due to the spin-orbit interaction.     

Crystallization waves in a dusty plasma

Crystallization waves in the dusty component of a complex plasma, which were recently observed experimentally, have been investigated numerically. The evolution of the system of charged microparticles whose interaction between each other is described by a screened Coulomb potential (Yukawa potential) has been numerically simulated using the molecular dynamics method. It has been shown that the process of the formation and propagation of a crystallization wave in such a system is fundamentally three-dimensional. Analysis of the local structure of dust particles behind the crystallization wave front indicates the coexistence of different types of the crystal lattice including the metastable phase, i.e., a nonequilibrium phase transition.     

Spin waves in Hubbard model

Gutzwiller's variational method has been used to study the spin waves in the ferromagnetic state of a narrow band. The spin wave energies are investigated in both the nondegenerate and the doubly degenerate bands. The electron correlation restricts the spin excitations and so improves the RPA solutions of the magnon energies. It is found that the bare intra-atomic interaction energies in the RPA solutions are replaced by smaller effective ones. In the case of a degenerate band model, contrary to the constant value as predicted by RPA, the Stoner gap parameter is reduced by the correlation effect.     

Chirality waves in two-dimensional magnets

We theoretically show that moderate interaction between electrons confined to move in a plane and localized magnetic moments leads to formation of a noncoplanar magnetic state. The state is similar to the Skyrmion crystal recently observed in cubic systems with the Dzyaloshinskii-Moriya interaction; however, it does not require spin-orbit interaction. The noncoplanar magnetism is accompanied by the ground-state electrical and spin currents, generated via the real-space Berry phase mechanism. We examine the stability of the state with respect to lattice discreteness effects and the magnitude of magnetic exchange interaction. The state can be realized in a number of transition metal and magnetic semiconductor systems.     

Two-dimensional nonlinear electromagnetic waves in a carbon nanotube array

Physics of the Solid State - The interaction of electromagnetic waves with carbon nanotubes has been investigated theoretically. The dynamics of nonlinear electromagnetic waves is considered in...     

Interaction of strongly nonlinear waves on the free surface of a dielectric liquid in a horizontal electric field

The nonlinear dynamics of the free surface of an ideal dielectric liquid with a large relative permittivity in a strong horizontal electric field has been considered. It has been demonstrated that the interaction between oppositely propagating solitary waves in arbitrary geometry is elastic: they conserve their energy and momentum. The interaction between waves has been numerically simulated with the use of conformal variables. It has been shown that the interaction deforms the waves; this effect is weak for waves with a relatively small amplitude: deformation for oppositely propagating waves with the identical shape is determined by the fourth power of their amplitude. At multiple collisions of strongly nonlinear waves, a tendency to the formation of singularities, i.e., points with a high energy density of the field, is observed.     

Long-range interaction of picosecond solitons through excitation of acoustic waves in optical fibers

We present the theory of electrostrictional interaction of soliton pulses in optical fibers. Solitons excite acoustic waves propagating in the direction transverse to the fiber axis. Scattering of optical radiation on these waves leads to a timing jitter of the optical pulses arrival time. We consider this effect as nonlinear self-scattering of light on acoustic waves. Because of the fact that a value of acoustic lifetime can reach a value of about 100 ns self-scattering on acoustic waves can be observed for a single optical pulse as well as for an optical pulse sequence as a whole. The value of single soliton self-frequency shift due to excitation of acoustic waves as a function of soliton duration have been obtained. For soliton duration _sol > 14 ps an acoustic wave soliton self-frequency shift is larger than the Raman soliton self-frequency shift.The obtained theoretical results describe well the long-range interaction of soliton pulse trains in an optical fiber. The value of bit error rate due to electrostrictional interaction of optical pulses in high bit rate, ultra long soliton communication systems have been obtained.     

Acousto-optic interaction with leaky surface acoustic waves in Y-cut LiTaO3 crystals

The acousto-optic interaction with leaky surface acoustic wave radiation into the bulk of YX-cut LiTaO₃ crystals has been investigated. The light incidence and diffraction angles corresponding to the strongest acousto-optic interaction were calculated and measured as functions of the acoustic wave frequency. The dependencies of the diffracted light intensity on the amplitude of radio-frequency voltage applied to the interdigital transducer (IDT) were studied. Our acousto-optic measurements revealed generation, by the IDTs, of slow shear bulk acoustic waves propagating at different angles depending on their frequency. A secondary acousto-optic interaction from the bulk waves radiated by the receiving IDT has been studied.     

Propagation of ultrasonic waves in neptunium monochalcogenides

The ultrasonic attenuation and acoustic coupling constants due to phonon–phonon interaction and thermoelastic relaxation mechanisms have been studied for longitudinal and shear waves in B₁ structured neptunium monochalcogenides NpX (X: S, Se, Te) along 〈1 0 0〉 direction in the temperature range 100–300 K. The second and third order elastic constants (SOEC and TOEC) of the chosen monochalcogenides are also computed for the evaluation of ultrasonic parameters. The ultrasonic attenuation due to phonon–phonon interaction process is predominant over thermoelastic relaxation process in these materials. The ultrasonic attenuation in NpTe has been found lesser than other materials NpS, NpSe and GdY (Y: P, As, Sb and Bi). The semiconducting or semimetallic nature of neptunium monochalcogenides can be well understood with the study of thermal relaxation time. Total ultrasonic attenuation in these materials is found to be quadratic function of temperature. The nature of NpTe is very similar to semimetallic GdP. The mechanical and ultrasonic study indicates that NpTe is more reliable, perfect, flawless material.     

Dust acoustic waves in a nonequilibrium dusty plasma

With the use of the method of moments applicable for any values of the parameter of the nonideality of a dusty plasma and the hydrodynamic approach applicable only for small nonideality parameters, the theory of waves and oscillations of a complex plasma has been generalized to the case of a two-exponential interaction potential. It has been shown that the hydrodynamic approach and method of moments give the same dispersion relation for small nonideality parameters. It has been demonstrated that the velocity of dust acoustic waves in the long- and short-wavelength regions is determined by the small and large screening constants, respectively. It has been shown that the velocity of dust acoustic waves in nonequilibrium plasma is much higher than that obtained in the Debye screening theory for equilibrium plasma. In the hydrodynamic approach, the importance of the inclusion of the self-consistent mutual effect of the dust, electron, and ion components, and sinks of electrons and ions on dust particles, which lead to a noticeable change in the parameters of the interaction potential of dust particles, has been demonstrated.     

Self-modulation of acoustic waves in resonant bars

Observations of the induced transparency in the oscillations of a glass bar containing an “artificial crack” in the form of a saw-cut with a tightly inserted small metal plate are reported. In such a configuration, the increase of the resonator quality factor with increasing wave amplitude (denoting a decrease of dissipation which will be referred to as self-induced transparency) has been observed indicating an important role of the amplitude-dependent losses introduced by the inter-surface contacts. The self-induced transparency manifests itself also by the discontinuities (jumps) in the acoustic wave amplitude measured as a function of sweeping excitation frequency around the sample eigenfrequencies and by a self-modulation instability of the primary acoustic wave. This instability leads to the generation of side-lobes in the wave spectrum near the fundamental excitation frequency. The developed theoretical model confirms that all these observations can be self-consistently attributed to nonlinearity of the sound dissipation process. Possible physical mechanisms of the nonlinear dissipation are discussed. Although self-modulation has already been observed in nonlinear acoustical systems, to the knowledge of the authors, the reported data constitute the first observation of the instabilities due to essentially dissipative system behaviour that requires neither nonlinear elasticity nor multimode interaction.     

Superconductivity and spin density waves

In the electron-electron interaction the r-space structure caused by magnetic fluctuations at the phase transition from a nonmagnetic metal to an antiferromagnetic metal gives rise to a d-wave attractive interaction for Cooper pairing. This is a contribution to some total electron-electron interaction which in total may or may not give rise to Cooper pairing and superconductivity.     

Electron plasma waves generation in suddenly created isotropicplasma

Electron plasma waves excitation in suddenly created isotropic plasma as a result of weak nonlinear interaction of linearly polarized plane electromagnetic (EM) wave and electrons has been considered. By the use of standard perturbation method the problem is solved in closed form for the case of a simple harmonic source EM wave. The appearance of the second harmonic and time independent modes have been demonstrated. The efficiency of excitation of these modes is possible to control by varying the frequency of the source wave     

Spin waves in a Bose-Einstein--condensed atomic spin chain

The spin dynamics of atomic Bose-Einstein condensates confined in a one-dimensional optical lattice is studied. The condensates at each lattice site behave like spin magnets that can interact with each other through both the light-induced dipole-dipole interaction and the static magnetic dipole-dipole interaction. We show how these site-to-site dipolar interactions can distort the ground-state spin orientations and lead to the excitation of spin waves. The dispersion relation of the spin waves is studied and possible detection schemes are proposed.     

Inelastic neutron scattering measurement of spin waves and magnetic interactions in NiO

The dispersion relation E(q) for spin waves in NiO, a Type II f.c.c. antiferromagnet, has been measured at 78°K. Values for the isotropic exchange interactions have been determined by fitting the Hamiltonian to the data. The next nearest neighbour interaction is found to dominate and the small nearest neighbour interaction is ferromagnetic in sign, in agreement with simple overlap theory.