Interacting topological magnons in a checkerboard ferromagnet

This work is devoted to studying the magnon–magnon interaction effect in a two-dimensional checkerboard ferromagnet with the Dzyaloshinskii–Moriya interaction. Using a first-order Green function method, we analyze the influence of magnon–magnon interaction on the magnon band topology. We find that Chern numbers of two renormalized magnon bands are different above and below the critical temperature, which means that the magnon band gap-closing phenomenon is an indicator for one topological phase ...     

Quantum Solitary Wave Solutions in a Ferromagnetic Chain with Nearest- and Next-Nearest-Neighbor Interaction

The quantum solitary wave solutions in a one-dimensional ferromagnetic chain is investigated by using the Hartree-Fock approach and the multiple-scale method. It is shown that quantum solitary wave solutions can exist in a ferromagnetic system with nearest- and next-nearest-neighbor exchange interaction, and at the certain value of the first Brillouin zone, the solitary wave solution of the Hartree wave function becomes the intrinsic localized mode.     

Exact soliton solutions in anisotropic ferromagnetic wires with Dzyaloshinskii–Moriya interaction

We theoretically investigate the exact soliton solutions of anisotropic ferromagnetic wires with Dzyaloshinskii–Moriya interaction. For example, we give the bright and black soliton solutions. From these results we find that the Dzyaloshinskii–Moriya interaction affects the existence region of soliton, spin-wave transport, and soliton dynamic properties. As the Dzyaloshinskii–Moriya interaction grows, the soliton width is widened, which provides a way to control the soliton dynamics.     

Magnon energy gap in a four-layer ferromagnetic superlattice

The magnon energy band in a four-layer ferromagnetic superlattice is studied by using the linear spin-wave approach and Green＇s function technique. It is found that three modulated energy gaps exist in the magnon energy band along Kx direction perpendicular to the superlattice plane. The spin quantum numbers and the interlayer exchange couplings all affect the three energy gaps. The magnon energy gaps of the four-layer ferromagnetic superlattice are different from those of the three-layer one. For the four-layer ferromagnetic superlattice, the disappearance of the magnon energy gaps △ω12, △ω23 and △ω34 all correlates with the symmetry of this system. The zero energy gap △ω23 correlates with the symmetry of interlayer exchange couplings, while the vanishing of the magnon energy gaps △ω12 and △ω34 corresponds to a translational symmetry of x-direction in the lattice. When the parameters of the system deviate from these symmetries, the three energy gaps will increase.     

Frozen Quantum Coherence for a Central Two-Qubit System in a Spin-Chain Environment

We investigate the dynamics of coherence for a central two-qubit system coupled to an XY spin chain with the Dzyaloshinsky–Moriya interaction. It is found that a sudden transition of coherence exists near the critical point in the weak-coupling case, and an oscillatory envelope appears in the strong-coupling case. In both cases the freezing phenomenon of coherence can be found.     

Solitons and intrinsic localized modes in a one-dimensional antiferromagnetic chain

By use of the Hartree approximation and the method of multiple scales, we investigate quantum solitons and intrinsic localized modes in a one-dimensional antiferromagnetic chain. It is shown that there exist solitons of two different quantum frequency bands: i.e., magnetic optical solitons and acoustic solitons. At the boundary of the Brillouin zone, these solitons become quantum intrinsic localized modes: their quantum eigenfrequencies are below the bottom of the harmonic optical frequency band and above the top of the harmonic acoustic frequency band.     

Efect of Varying Dzyaloshinskii–Moriya Interaction on the Bistable Nano-Scale Soliton Switching

The efect of Dzyaloshinskii–Moriya(D-M) interaction on the bistable nano-scale soliton switching ofers the possiblity of developing a new innovative approach for data storage technology. The dynamics of Heisenberg ferromagnetic spin system is expressed in terms of generalized inhomogeneous higher order nonlinear Schro¨dinger(NLS) equation. The bistable soliton switching in the ferromagnetic medium is established by solving the associated coupled evolution equations for amplitude and velocity of the soliton using the fourth order Runge–Kutta method numerically.     

Spin-Wave Modes in Exchange-Coupled FePt/FeNi Bilayer Films

A simple magnetic modulation structure of the exchange-coupling FePt/FeNi bilayer film is fabricated and studied for its magnetization dynamics using time-resolved magneto-optical polar Kerr spectroscopy. It is found that two spin-wave modes can be excited. One is fixed at -3.2 GHz in frequency for any external field and may serve as a frequency-stabilized spin-wave filter, while the other is external field dependent. In contrast, only the external field-dependent mode is excited in single-layer FeNi, supporting the localized origin of the mode at -3.2 GHz, which is confined to a thin exchange-coupling region. The other external field-dependent mode in frequency is attributed to the Kittel mode.     

Frequency in Middle of Magnon Band Gap in a Layered Ferromagnetic Superlattice

The frequency in middle of magnon energy band in a five-layer ferromagnetic superlattice is studied by using the linear spin-wave approach and Green＇s function technique. It is found that four energy gaps and corresponding four frequencie in middle of energy gaps exist in the magnon band along Kx direction perpendicular to the superlattice plane. The spin quantum numbers and the interlayer exchange couplings all affect the four frequencies in middle of the energy gaps. When all interlayer exchange couplings are same, the effect of spin quantum numbers on the frequency wg1 in middle of the energy gap Δw12 is complicated, and the frequency wg1 depends on the match of spin quantum numbers in each layer. Meanwhile, the frequencies wg2, wg3, and wg4 in middle of other energy gaps increase monotonously with increasing spin quantum numbers. When the spin quantum numbers in each layer are same, the frequencies wg1, wg2, wg3, and wg4 all increase monotonously with increasing interlayer exchange couplings.     

The characteristic of power flow in broad band dynamic vibration absorber

DVA (dynamic vibration absorber) is good for restrain of the resonance vibration in low frequency, especially under the condition that there are only one mode or two modes in a frequency band. It seems rather difficult to control the resonance vibration of elastic structures in high frequency, since usually there are so many modes in high frequency band. The broad band DVA is brought forward to reduce the resonance vibration of elastic structures. The broad band DVA is designed on the basis of the characteristic of power flow in structure in this paper. The broad band DVA is effective on absorbing the resonance vibration power flow of the most important modes. The ability of absorbing vibration for the broad band DVA is analyzed in detail. The results obtained in this paper provide a basis for the optimization design of the broad band DVA and the optimization positions on structures.     

Topological magnon insulator with Dzyaloshinskii–Moriya interaction under the irradiation of light

The topological magnon insulator on a honeycomb lattice with Dzyaloshinskii–Moriya interaction(DMI) is studied under the application of a circularly polarized light.At the high-frequency regime, the effective tight-binding model is obtained based on Brillouin–Wigner theory.Then, we study the corresponding Berry curvature and Chern number.In the Dirac model, the interplay between a light-induced handedness-dependent effective DMI and intrinsic DMI is discussed.     

Propagation of chirped solitons on a cw background in a non-Kerr quintic medium with self-steepening effect

We study the existence and stability of envelope solitons on a continuous-wave background in a non-Kerr quintic optical material exhibiting a self-steepening effect. Light propagation in such a nonlinear medium is governed by the Gerdjikov–Ivanov equation. We find that the system supports a variety of localized waveforms exhibiting an important frequency chirping property which makes them potentially useful in many practical applications to optical communication. This frequency chirp is found to...     

Entanglement in a two-spin system with long-range interactions

The quantum entanglement between two spins in the Ising model with an added Dzyaloshinsky–Moriya(DM) interaction and in the presence of the transverse magnetic field is studied. The exchange interaction is considered as a function of the distance between spins. The negativity as a function of magnetic field, exchange and DM interaction is calculated.The effect of the distance between spins is studied based on the negativity. In addition, the effect of the thermal fluctuation on the negativity is also investigated.     

Selective flattening of magnon bands in kagome-lattice ferromagnets with Dzyaloshinskii-Moriya interaction

There is growing interest in revealing exotic properties of collective spin excitations in kagome-lattice ferromagnets such as magnon Hall effects,topological magnon insulators,and flat magnon bands.Using the well-established nearest-neighbor Heisenberg ferromagnet model with Dzyaloshinskii-Moriya interaction (DMI),in this study we uncover intriguing new aspects in the selectivity and topology of flat magnon bands.Among the three magnon bands (except for the top one,which is flat in the absence of DMI),we observe that each of the three bands can be selectively flattened at the critical DMI of ■.With a general DMI,the magnon bands become non-flat;however,there are nested lines that create a David star pattern for all three magnon bands whose flatness is robust during changing exchange coupling or DMIs.Contrary to prevailing belief,we show that each of the three flat bands is actually topologically trivial at critical DMIs.Furthermore,we show that while the middle band remains topologically trivial,for the other two bands,D=0 corresponds to the topological phase transition where their Chern numbers get interchanged;when ■,the system undergoes a phase transition to the nonferromagnetic state.These central findings increase our understanding of spin excitations for future magnonics applications.     

Dynamics of high-frequency modulated waves in a nonlinear dissipative continuous bi-inductance network

This paper presents intensive investigation of dynamics of high frequency nonlinear modulated excitations in a damped bimodal lattice. The effects of the dissipation are considered through a linear dissipation coefficient whose evolution in terms of the carrier wave frequency is checked. There appears that the dissipation coefficient increases with the carrier wave frequency. In the linear limit and for high frequency waves, study of the asymptotic behavior of plane waves reveals the existence of two additional regions in the dispersion curve where the modulational phenomenon is observed compared to the lossless line. Based on the multiple scales method exploited in the continuum approximation using an appropriate decoupling ansatz for the voltage of the two different cells, it appears that the motion of modulated waves is described by a dissipative complex Ginzburg–Landau equation instead of a Korteweg–de Vries equation. We also show that this amplitude wave equation admits envelope and hole solitons in the high frequency mode. From basic sources, we design a programmable electronic generator of complex signals with desired characteristics, which delivers signals exploited as input waves for all our numerical simulations. These simulations are performed in the LTspice software that uses realistic components and give the results that corroborate perfectly our analytical predictions.     

The phenomenon of even bulk modes variance in a ferromagnetic A--A bilayer system

The eigenproblems of spin waves in a symmetrical ferromagnetic bilayered system with periodic boundary conditions are solved using the interface-rescaling approach (IRA). The results show that interface coupling between two sublayers would not change the excitation energy of odd bulk modes, but change excitation energy of even bulk modes. We call this peculiar phenomenon the phenomenon of even bulk mode variance (PEBMV). There are two kinds of mechanisms which cause PEBMV: phase reversal and phase translation of the magnon at the interface, corresponding, respectively, to the antiferromagnetic and ferromagnetic interface coupling cases. PEBMV embodies the selective effect of the interface on different bulk magnons.     

Polar interface and surface optical vibration spectra in multi-layer wurtzite quantum wires： transfer matrix method

The polar interface optical （IO） and surface optical （SO） phonon modes and the corresponding Froehlich electron phonon-interaction Hamiltonian in a freestanding multi-layer wurtzite cylindrical quantum wire （QWR） are derived and studied by employing the transfer matrix method in the dielectric continuum approximation and Loudon＇s uniaxial crystal model. A numerical calculation of a freestanding wurtzite GaN/AlN QWR is performed. The results reveal that for a relatively large azimuthal quantum number m or wave-number kz in the free z-direction, there exist two branches of IO phonon modes localized at the interface, and only one branch of SO mode localized at the surface in the system. The degenerating behaviours of the IO and SO phonon modes in the wurtzite QWR have also been clearly observed for a small kz or m. The limiting frequency properties of the IO and SO modes for large kz and m have been explained reasonably from the mathematical and physical viewpoints. The calculations of electron-phonon coupling functions show that the high-frequency IO phonon branch and SO mode play a more important role in the electron phonon interaction.     

Dual Space Analyzing Based on Symmetry Properties for Phonons of Si Quantum Dot

Phonon modes in spherical Si quantum dots (QDs) with up to 7.9 nm in diameter are calculated by using the projection operators of the group theory into valence force field model. The phonons of dot modes in each of five irreducible representations (symmetries) are classified by using a dual space analysis method. It is found that the bulk-like modes with localization radius much smaller than the dot‘s radius have clearly pronounced bulk specific-κdefinite bulk band (one in six modes). In Si dots of all sizes, each specific bulk-like dot mode has specific symmetry.TO dot modes and bulk-like X-derived TA and LA dot modes red-shift in frequency with decreasing dot size. There is almost not LO/TO mixing for bulk-like modes. As for the surface-like modes localized at the periphery of the dot,their eigenmodes have not a dominant bulk specific-κ point parentage or a dominant BZ parentage around some special point. They are a superposition of many bulk bands with κ from all over the bulk BZ. They have much significant mode mixing than the bulk-like phonons. The classification of dot modes based on the symmetry of group theory will bring advantageous to the discussion of Ramam spectrum, electron-phonon interaction and other phonon-assisted effects in QDs.     

Electron-Phonon Interaction in an Annular Quantum Dot

The confined longitudinal-optical （LO） phonon and surface-optical （SO） phonon modes of a free-standing annular cylindrical quantum dot are derived within the framework of dielectric continuum approximation. It is found that there exist two types of SO phonon modes： top SO （TSO） mode and side SO（SSO） mode in a cylindrical quantum annulus. Numerical calculation on CdS annulus system has been performed. Results reveal that the two different solutions of SSO mode distribute mainly at the inner or outer surfaces of the annulus. The dispersion relations and the coupling intensions of phonons in a quantum annulus are compared with those in a cylindrical quantum dot. It is found that the dispersion relations of the two different structures are similar, but the coupling intension of the phonon-electron interaction in quantum annulus is larger than that in quantum dot. The Hamiltonians describing the free phonon modes and their interactions with electrons in the system are also derived.     

Coupling between Collective Excitations of a Bose--Einstein Condensate and Modulated Interactions

We investigate collective excitations of a Bose Einstein repulsive interactions, and analytically demonstrate that condensate in the presence of temporal modulation of the modulated interaction can drive the condensate to oscillate with the external modulation frequency, and that the interaction couples with the eigen modes of the condensate collective excitations, which was previously considered to be independent of interaction. When the external modulation frequency approaches or is far away from the eigen frequency of the density monopole mode, the condensate shows resonant or beating behaviour.