Observation of self-generation of dark envelope solitons for spin waves in ferromagnetic films

We have performed experiments in which self-generation of dark envelope solitons for spin waves at microwave frequencies were obtained. Stable self-generation of dark solitons was observed in a ring consisting of tangentially magnetized yttrium iron garnet film and a microwave signal amplifier. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 3, 229–233 (10 August 1998)     

Low-frequency relativistic electromagnetic solitons in collisionless plasmas

A relativistic electromagnetic soliton solution in the model of a one-dimensional, unbounded, cold, collisionless plasma is obtained without using the envelope approximation. The breaking of solitons with over-critical amplitudes is observed. The stability of undercritical solitons and the breaking of overcritical solitons are demonstrated by a particle-in-cell computer simulation. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 1, 33–38 (10 July 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Stochastic excitation of a stimulated spin echo

The excitation of a stimulated spin echo by two coherent pulses of Gaussian white noise and a δ-function-like radio pulse is studied. The mean value of the complex envelope of the echo is obtained by solving the Bloch equations. The behavior of the mean value of the envelope of the stimulated echo is investigated for a Lorentzian shape of the inhomogeneously broadened absorption line. It is shown that in an excitation regime which is linear for noise pulses the envelope corresponds to the Fourier transform of the line-shape function. Nonlinear distortions of the mean value of the envelope of a stimulated echo can arise outside the linear excitation regime. Zh. Tekh. Fiz. 67, 100–104 (October 1997)     

Observation of spin-wave envelope Dark solitons in ferromagnetic films

Microwave spin-wave envelope dark solitons were experimentally observed for the first time. Dark solitons with zero minimum amplitude were generated by two-frequency excitation of input spin waves with a fixed amplitude. Nonlinear interaction between these two traveling waves gave rise to periodic sequences of dark solitons in a ferromagnetic film.     

Mechanism for the appearance and randomization of the self-modulation of high-intensity spin waves

Modulational instability of high-intensity spin waves exhibiting amplification is studied in magnetic films under conditions of three-magnon decay. The mechanisms for this effect and for randomization of the envelope under self-modulation are identified. Zh. Tekh. Fiz. 69, 100–103 (August 1999)     

Envelope solitons of electromagnetic spin waves in an artificial layered multiferroic

The nonlinear wave properties of an artificial multiferroic medium consisting of a ferroelectric layer and a ferromagnetic layer have been studied. The simultaneous effect of wave nonlinearities of both layers on the formation and propagation of envelope solitons has been analyzed. It has been shown that bright envelope solitons of electromagnetic spin waves can appear in such a medium owing to the wave nonlinearity of ferroelectric layer. In order to confirm the theoretical results, the coefficients of the nonlinear Schrödinger equation have been calculated and this equation has been solved numerically.     

Envelope solitons in a medium with strong nonlinear damping

The formation of microwave spin-wave envelope solitons in the ferrite film of yttrium iron garnet in the presence of strong nonlinear damping has been experimentally found and investigated. The solitons are formed due to the four-wave interactions of spin waves when the characteristic time of wave modulation-instability development is much shorter than the time for establishing the generation of short-wavelength magnons. The presence of nonlinear damping allows the excitation of spin-wave envelope solitons by means of long microwave pulses.     

Dynamic topological solitons in a two-dimensional ferromagnet

It is shown that stable, skyrmion-type, dynamic solitons can be constructed for a wide class of two-dimensional models of anisotropic ferromagnets. These solitons are stabilized as a result of the conservation of various integrals of motion: the z projection of the total spin S _z or the orbital angular momentum L _z of the magnetization field. A class of two-parameter solitons with quite complicated (almost periodic) magnetization-field dynamics exists for a purely uniaxial model (in the sense of both spin and spatial rotations) with maximum symmetry. Stable solitons with periodic magnetization dynamics exist for ferromagnets with lower symmetry (only S _z or L _z or the total angular momentum J _z =L _z +S _z is conserved). Zh. éksp. Teor. Fiz. 115, 1511–1530 (April 1999)     

Thirring combo-solitons with cubic nonlinearity and spatio-temporal dispersion

Abstract

The vector-coupled nonlinear Schrödinger equation, which can be applied to describe the propagation of Thirring optical solitons in birefringent ?bers with Kerr law nonlinearity, detuning, intermodal dispersion and spatiotemporal dispersion, has been studied analytically. By means of the complex envelope function ansatz, exact Thirring bright-dark combosolitons are reported, and the properties of these solitons are discussed.     

Soliton regimes of surface magnetostatic wave propagation in a magnet-semiconductor structure

The nonlinear properties of exchange-free surface magnetostatic spin waves in a layered structure containing films of a ferromagnet and a semiconductor are investigated theoretically. The stability of nonlinear surface magnetostatic waves relative to longitudinal disturbances is investigated using the envelope evolution equation in the weak-nonlinearity approximation. It is shown that, under certain conditions, a surface spin-wave pulse propagates in the form of an envelope soliton. Calculations are performed for the case of an yttrium iron-garnet-indium antimonide structure. Fiz. Tverd. Tela (St. Petersburg) 41, 1272–1275 (July 1999)     

Slow relaxation experiments in disordered charge and spin density waves: collective dynamics of randomly distributed solitons

We show that the dynamics of disordered charge density waves (CDWs) and spin density waves (SDWs) is a collective phenomenon. The very low temperature specific heat relaxation experiments are characterized by: (i) “interrupted” ageing (meaning that there is a maximal relaxation time); and (ii) a broad power-law spectrum of relaxation times which is the signature of a collective phenomenon. We propose a random energy model that can reproduce these two observations and from which it is possible to obtain an estimate of the glass cross-over temperature (typically T _g≃ 100-200 mK). The broad relaxation time spectrum can also be obtained from the solutions of two microscopic models involving randomly distributed solitons. The collective behavior is similar to domain growth dynamics in the presence of disorder and can be described by the dynamical renormalization group that was proposed recently for the one dimensional random field Ising model [D.S. Fisher, P. Le Doussal, C. Monthus, Phys. Rev. Lett. 80, 3539 (1998)]. The typical relaxation time scales like ∼τexp(T _g/T). The glass cross-over temperature T_g related to correlations among solitons is equal to the average energy barrier and scales like T _g∼ 2xξΔ. x is the concentration of defects, ξ the correlation length of the CDW or SDW and Δ the charge or spin gap. Received 12 December 2001     

Observation of spin-wave envelope solitons in periodic magnetic film structures

The formation and propagation of light and dark microwave spin-wave envelope solitons in a periodic magnetic film structure have been observed. The periodic structure was manufactured on the basis of the single-crystal film of iron-yttrium garnet and a lattice of copper strips placed on the surface of the film perpendicularly to the propagation direction of carrying spin waves. The solitons are generated at frequencies corresponding to the band gap in the spectrum of the spin waves of the periodic structure, which is due to the first Bragg resonance.     

On the structure and stability of two-dimensional dynamic solitons in ferromagnets

Dynamic solitons in uniaxial and orthorhombic magnets are investigated. It is shown that centrosymmetric solitons can be unstable with respect to elliptic distortions. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 12, 899–903 (25 June 1997)     

Self-generation of spin-wave envelope soliton trains with different periods

The self-generation of periodic spin-wave envelope soliton trains of microwave spin waves in active rings based on ferromagnetic films is studied experimentally. The trains of bright solitons with different periods are self-generated in the same ring due to the frequency-selective control of the attenuation of spin waves circulating in an active ring.     

Generation and interaction of large-amplitude solitons

The results of a numerical simulation of the interaction and generation of solitons in nonlinear integrable systems which admit the existence of very-large-amplitude solitons are reported. The nonlinear integrable system chosen for study is the Gardner equation, particular examples of which are the Korteweg-de Vries equation (for quadratic nonlinearity) and a modified Korteweg-de Vries equation (for cubic nonlinearity).It is shown that during the evolution process solitons of opposite polarity appear on the crest of the maximum soliton. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 9, 628–633 (10 May 1998)     

Pulsed-ESR Study of Spin Solitons as a Probe of Neutral-to-Ionic Phase Transition of TTF-CA Single Crystal

Ionic phase of charge-transfer crystal composed of tetrathiafulvalene (TTF) and p -chloranil (CA) has been studied by two-pulse electron-spin echo (ESE) at 4 K. By measuring the angular dependence of the field-swept ESE spectrum, at least three kinds of paramagnetic centers have been resolved, which are presumably ascribed to spin solitons formed at domain boundary. With varying the time separation between the microwave pulses, envelope modulations due to anisotropic hyperfine interaction have been detected. By analyzing the modulation, we have firstly obtained ENDOR spectrum of the spin solitons. Response of the ESE intensity for the optical excitation has been also examined.     

Giant waves in weakly crossing sea states

The formation of rogue waves in sea states with two close spectral maxima near the wave vectors k ₀ ± Δk/2 in the Fourier plane is studied through numerical simulations using a completely nonlinear model for long-crested surface waves [24]. Depending on the angle θ between the vectors k ₀ and Δk, which specifies a typical orientation of the interference stripes in the physical plane, the emerging extreme waves have a different spatial structure. If θ ≲ arctan(1/√2), then typical giant waves are relatively long fragments of essentially two-dimensional ridges separated by wide valleys and composed of alternating oblique crests and troughs. For nearly perpendicular vectors k ₀ and Δk, the interference minima develop into coherent structures similar to the dark solitons of the defocusing nonlinear Schroedinger equation and a two-dimensional killer wave looks much like a one-dimensional giant wave bounded in the transverse direction by two such dark solitons.     

Hard soliton excitation regime: Stability investigation

The problem of the stability of one-dimensional solitons in the hard regime of soliton excitation, where the matrix element of the four-wave interaction has an additional smallness, is studied. It is that shown for optical solitons striction can weaken the Kerr nonlinearity. It is shown that solitons with a finite amplitude discontinuity at the critical soliton velocity, equal to the minimum phase velocity of linear waves, are unstable while solitons with a soft transition remain stable with respect to one-dimensional perurbations. Two-and three-dimensional solitons near threshold are unstable with respect to modulation perturbations. Zh. éksp. Teor. Fiz. 116, 299–317 (July 1999)     

Self-action of intense electromagnetic radiation in an electron-positron vacuum

An analysis is done of the effects of self-action of intense coherent electromagnetic radiation in an electron-positron vacuum that is in homogeneous electric and magnetic fields. A modified version of the Heisenberg-Euler theory, in which the Lagrangian incorporates terms with field derivatives, is used to take into account vacuum dispersion. The nonphysical branch of the solutions of the dispersion equation is excluded by a transition to a quasioptical equation for the slowly varying field envelope, an equation that describes the propagation of radiation with allowance for diffraction, spatial-temporal dispersion, and vacuum nonlinearity. The existence of dark solitons (with an intensity gap) in the vacuum is shown to be present. Finally, self-focusing of radiation in a vacuum is demonstrated and the critical self-focusing power is determined. Zh. éksp. Teor. Fiz. 113, 513–520 (February 1998)