Vector solitons in semiconductor quantum dots

A theory of an optical vector soliton of self-induced transparency in an ensemble of semiconductor quantum dots is considered. By using the perturbative reduction method, the system of the Maxwell–Liouville equations is reduced to the two-component coupled nonlinear Schrödinger equations. It is shown that a distribution of transition dipole moments of the quantum dots and phase modulation changes significantly the pulse parameters. The shape of the optical two-component vector soliton with the sum and difference of the frequencies in the region of the carrier frequency is presented. The vector soliton can be reduced to the breather solution of self-induced transparency with a different profile. Explicit analytical expressions in the presence of single-excitonic and biexcitonic transitions for the optical vector soliton are obtained with realistic parameters which can be reached in current experiments.     

Phase-modulated soliton of self-induced transparency

A theory of optical self-induced transparency for a two-component soliton in the presence of phase modulation is developed. It is shown that, under these conditions, it is possible to generate a vector soliton with characteristic parameters of oscillations with the sum and difference frequencies in the region of the carrier wave frequency. Explicit analytical expressions for nonlinear wave parameters under experimentally implemented conditions are given. In particular case, a well-known solution in the form of a breather is obtained.     

Inhomogeneous magnetostriction states in uniaxial ferromagnetic films

Surface magnetoelastic Love waves and nonuniform distributions of the magnetization and elastic strains are investigated in a uniaxial ferromagnetic film on a massive nonmagnetic substrate in a tangential external magnetic field. A new inhomogeneous phase is predicted having spatial modulation of the order parameter, arising from magnetostrictive coupling of the magnetization with lattice strains near the interface of the magnetoelastic and elastic media. It is shown that, at some critical magnetic field H _c, different from the orientational transition field in an isolated sample, a magnetoelastic Love wave propagating parallel to the magnetization vector in the film plane becomes unstable. The frequency and group velocity of the wave vanish at wave number k=k _c≠0 and the wave freezes, forming a domain structure localized in the film and adjoining substrate. Fiz. Tverd. Tela (St. Petersburg) 41, 665–671 (April 1999)     

Vacuum-deposited wave-guiding layers on STW resonators based on LiTaO3 substrate as love wave sensors for chemical and biochemical sensing in liquids

A promising approach to apply the Love wave concept to commercially available low-loss surface acoustic wave (SAW) devices of the type Murata SAF 380 is presented. Thin wave-guiding layers of variable thickness are coated on the piezoelectric substrate of the devices. Two different layer materials were used: sputtered SiO₂ and a new polymer in this field, parylene C (poly-[2-chloro-p-xylylene]). Insertion loss, resonance frequency, frequency changes during protein precipitation and noise of the devices are discussed as a function of the thickness of the wave-guiding layer. It is demonstrated that the application of an optimized wave-guiding layer increases the sensitivity. When using SiO₂ as wave-guiding layer, an optimum layer thickness of 4 μm leads to a detection limit of 1.7 pg/mm². Therefore, the detection limit is improved by factor 7.7 as compared to uncoated SAW devices. Parylene-coated devices reach a detection limit of 2.9 pg/mm² at an optimum layer thickness of 0.5 μm. This corresponds to an improvement by factor 4.3. As the SAW devices used in this study are commercially available at low costs, applying appropriate wave-guiding layers permits an application as chemical or biochemical sensors with excellent sensitivities. Moreover, parylene-coated devices combine the sensitivity increase by excitation of Love waves with an excellent protective effect against corrosive attacks by the surrounding medium. Therefore, these sensors are most suitable for biosensing in conducting buffer solutions.     

Acoustic scattering of a high-order Bessel beam by an elastic sphere

The exact analytical solution for the scattering of a generalized (or “hollow”) acoustic Bessel beam in water by an elastic sphere centered on the beam is presented. The far-field acoustic scattering field is expressed as a partial wave series involving the scattering angle relative to the beam axis and the half-conical angle of the wave vector components of the generalized Bessel beam. The sphere is assumed to have isotropic elastic material properties so that the nth partial wave amplitude for plane wave scattering is proportional to a known partial-wave coefficient. The transverse acoustic scattering field is investigated versus the dimensionless parameter ka(k is the wave vector, a radius of the sphere) as well as the polar angle θ for a specific dimensionless frequency and half-cone angle β. For higher-order generalized beams, the acoustic scattering vanishes in the backward (θ = π) and forward (θ = 0) directions along the beam axis. Moreover it is possible to suppress the excitation of certain resonances of an elastic sphere by appropriate selection of the generalized Bessel beam parameters.     

CW-pumped polarization-maintaining Brillouin fiber ring laser: I. Self-structuration of Brillouin solitons

Stimulated Brillouin scattering (SBS) of a cw-pump in a long optical fiber ring cavity generates for a given gain G, below a critical feedback R_crit, a backward soliton Stokes pulse at the roundtrip repetition rate, through resonant three-wave interaction between the optical pump wave and backward Stokes wave, and a high frequency (GHz) axial acoustic wave. In Part I, we perform a systematic experimental and numerical exploration of the whole soliton localisation domain for a large set of (G, R) parameters, in a polarization-maintaining Brillouin fiber ring laser in the best conditions of stability and coherence, and we confirm the excellent quantitative agreement of the coherent three-wave model and the experiments.     

High-frequency ultrasonic studies of the structural phase transition in an La<Subscript>0.875</Subscript>Sr<Subscript>0.125</Subscript>MnO<Subscript>3</Subscript> single crystal

The specific features of a phase transition from a disordered orbital state to an ordered orbital state in an La_0.875Sr_0.125MnO₃ single crystal are investigated using acoustic methods at a frequency f = 500 MHz. The phase transition is accompanied by a distortion of MnO₆ octahedra due to the cooperative Jahn-Teller effect and is a first-order phase transition, as judged from the sharp change observed in the damping of acoustic pulses, the acoustic wave velocity, and the temperature hysteresis. It is revealed that the parameters of the acoustic waves change significantly throughout the temperature range of existence of the cooperatively distorted structure. In an external magnetic field, the structural phase transition is shifted toward lower temperatures.     

Nonlinear theory of transverse perturbations of quasi-one-dimensional solitons

An averaged variational principle is applied to analyze the nonlinear effect of transverse perturbations (including diffraction) on quasi-one-dimensional soliton propagation governed by various wave equations. It is shown that parameters of the spatiotemporal solitons described by the cubic Schrödinger equation and the Yajima-Oikawa model of interaction between long-and short-wavelength waves satisfy the spatial quintic nonlinear Schrödinger equation for a complex-valued function composed of the amplitude and eikonal of the soliton. Three-dimensional solutions are found for two-component “bullets” having long-and short-wavelength components. Vortex and hole-vortex structures are found for envelope solitons and for two-component solitons in the regime of resonant long/short-wave coupling. Weakly nonlinear behavior of transverse perturbations of one-dimensional soliton solutions in a self-defocusing medium is described by the Kadomtsev-Petviashvili equation. The corresponding rationally localized “lump” solutions can be considered as secondary solitons propagating along the phase fronts of the primary solitons. This conclusion holds for primary solitons described by a broad class of nonlinear wave equations.     

乐甫波结冰状态监测的响应机理分析

提出了将冰层进行多孔介质等效方法,对冰层、液体/波导层/压电基底多层乐甫(Love)波导结构建立分层介质模型,利用部分波理论和边界条件精确推导,分析不同状态下的传感响应,求解结冰过程Love波速度及声波衰减的变化,获得结冰过程中的声学传感机制。为了验证理论分析,实验制作了200 MHz的36°LiTaO₃/SiO₂波导结构的Love波器件,并构建模拟环境的试验系统对研制器件进行了实验测试。实验结果表明,利用Love波的工作频率以及插入损耗瞬变这一特征可以实现对结冰状态的准确监测。      

Brillouin scattering in KH3 (SeO3)2 above the transition temperature

The Brillouin scattering measurement in KH₃(SeO₃)₂ above the transition temperature shows a large anomaly in hypersonic velocity of the transverse wave with the wave vector q = [010] and the polarization ξ = [001], which indicates acoustic phonon softening.     

Spin-wave resonance in three-layer NiFe/DyxCo1−x /NiFe films as a method for detecting structural inhomogeneities in amorphous DyxCo1−x Layers

The standing spin-wave spectrum was studied by spin-wave resonance in three-layer Ni₈₀Fe₂₀/Dy_xCo_1?x /Ni₈₀Fe₂₀ films with an amorphous interlayer of DyCo alloy in the region of compensation compositions. It is shown that the spin-wave resonance (SWR) spectrum in the geometry k‖M is observed only for a planar system with a DyCo layer of precompensation composition. In the k⊥M geometry, the SWR spectrum was observed for the DyCo systems with both pre-and postcompensation compositions. The exchange stiffness was analyzed as a function of the DyCo layer thickness to formulate a model of microheterophase structure for amorphous DyCo alloys in the compensation region, where the magnetic microstructure accounts for the dynamic and static magnetic characteristics of these materials.     

Drift ion acoustic solitons in an inhomogeneous 2-D quantum magnetoplasma

Linear and nonlinear propagation characteristics of quantum drift ion acoustic waves are investigated in an inhomogeneous two-dimensional plasma employing the quantum hydrodynamic (QHD) model. In this regard, the dispersion relation of the drift ion acoustic waves is derived and limiting cases are discussed. In order to study the drift ion acoustic solitons, nonlinear quantum Kadomstev-Petviashvilli (KP) equation in an inhomogeneous quantum plasma is derived using the drift approximation. The solution of quantum KP equation using the tangent hyperbolic (tanh) method is also presented. The variation of the soliton with the quantum Bohm potential, the ratio of drift to soliton velocity in the co-moving frame, , and the increasing magnetic field are also investigated. It is found that the increasing number density decreases the amplitude of the soliton. It is also shown that the fast drift soliton (i.e., v_*>u) decreases whereas the slow drift soliton (i.e., v_*<u) increases the amplitude of the soliton. Finally, it is shown that the increasing magnetic field increases the amplitude of the quantum drift ion acoustic soliton. The stability of the quantum KP equation is also investigated. The relevance of the present investigation in dense astrophysical environments is also pointed out.     

Excitation of ion acoustic waves at the difference frequency of two microwave beams in a semiconductor

This letter presents an investigation of the resonant excitation of the electrostatic ion acoustic wave at the difference frequency of two microwave beams in a semiconductor, viz., n-type InSb. The ponderomotive force at the difference frequency on electrons drives the ion acoustic wave at the difference frequency. The resonance conditions are satisfied over a wide range of semiconductor parameters. For typical plasma parameters of n-InSb and microwave beams of power densities 1 MW cm^?2, the power density of the excited ion acoustic wave is ≈ 1.76 kW cm^?2.     

Fermi resonance of optical one-phonon and acoustic two-phonon vibrations in light metals

It is shown that the anharmonicity of crystal lattice vibrations in light metals such as beryllium, can give rise to a Fermi resonance of optical one-phonon and acoustic two-phonon vibrations. New hybridized vibrational states are formed as a result of such a resonance interaction: biphonon and quasibiphonon vibrations and renormalized optical vibrations. Depending on the wave vector, these vibrational states can be both damped and stationary. The corresponding dispersion equation is obtained, whose solution made it possible to determine the spectrum of these vibrations (dispersion curves and the wave vector dependence of the damping for damped vibrations). It is shown that ultrafast damping of optical vibrations, similar to the well-known superradiance effect for Frenkel’ and Wannier-Mott excitons, is possible. Fiz. Tverd. Tela (St. Petersburg) 39, 542–546 (March 1997)     

Critical behavior of RMn2O5 oxides near the magnetic phase transition to a structure incommensurate in two spatial directions

A phase transition from the paramagnetic state to the long-period magnetic structure in RMn₂O₅ oxides with the star of the wave vector determining the incommensurability of long-range magnetic order in two spatial directions has been investigated. An effective Hamiltonian of the system that allows one to describe this transition in the framework of the renormalization group approach has been constructed. It has been shown that there is a stable critical point of transformations of this group at which there occurs a second-order phase transition. The critical indices have been found. The obtained results have been compared with the results for phase transitions occurring in these oxides in accordance with the star of the wave vector, which provides incommensurability in one of the spatial directions. It has been found that fluctuations of the four-component order parameter due to the low spatial symmetry of these compounds do not change the order of the phase transition, which was found in terms of the Landau theory.     

Weakly dissipative dust acoustic solitons in the presence of superthermal particles

An investigation of the linear and non‐linear properties of low‐frequency electrostatic (dust acoustic) waves in a collisional dusty plasma with negative dust grains, Maxwellian electrons, and κ ‐distributed ions is carried out. Low dust–neutral collisions accounting for dissipation (wave damping effect) is considered. The linear properties of dust acoustic excitations are discussed for varying values of relevant plasma parameters. It is shown that large wavelengths (beyond a critical value) are overdamped. In the limit of low dust–neutral collision rate, we have derived a damped Korteweg de Vries (KdV) equation by using the reductive perturbation technique. Supplemented by vanishing boundary conditions, the time‐varying solution of damped KdV equation leads to a weakly dissipative negative potential soliton. The soliton evolution with the damping parameter and other physical plasma parameters (superthermality, dust concentration, ion temperature) is delineated.     

Inelastic neutron scattering from transverse acoustic modes in K2SnCl6

In cubic K₂SnCl₆ the dispersion curve für q q; [110] of [1$\text{1}$0] polarized acoustic phonons has been measured at three temperatures near the phase transition temperature T_c1. The acoustic branch shows no temperature dependence in the low wave vector region and stiffens slightly near the X-point of the fcc-Brillouin zone as the temperature approaches the phase transition T_c1= 262 K from above. The results support a previously developed model on acoustic anomalies in this compound.     

Coexistence of superconductivity and magnetic order

The microscopic theory of simple antiferromagnetic superconductors is extended to structures where the magnetic order is described by a spin-density wave. For the case where the magnetic system is inherently ferromagnetic, the free energy of the combined system is minimized with respect to the amplitude and the wave vector of the spin-density wave. It is found that the wave vector depends very weakly on temperature. We apply the theory to the coexistence region in ErRh₄B₄, finding a first-order re-entry transition.     

Two wave collapses and a strange soliton in current carrying plasmas

A current driven plasma is analyzed in the two-fluid approach. A Lagrangian treatment of the charge neutral system results in a nonlinear scalar wave equation, which exhibits two different singular wave solutions. One wave collapse is associated with a density excavation, the other with a density compression. The latter represents the scenario of wave breaking and survives under charge separation. A new soliton solution is found just above threshold of linear instability of the charge nonneutral system in case of hot electrons. It is reminiscent of an ion acoustic KdV-soliton but differs from it in several respects such as in the propagation speed, in the strength and polarity of the electrostatic potential and in the spatial width. It is a finite ion temperature effect and disappears in the cold ion limit T_i → 0.