61 research outputs found
On modulational instability and energy localization in anharmonic lattices at finite energy density
The localization of vibrational energy, induced by the modulational
instability of the Brillouin-zone-boundary mode in a chain of classical
anharmonic oscillators with finite initial energy density, is studied within a
continuum theory. We describe the initial localization stage as a gas of
envelope solitons and explain their merging, eventually leading to a single
localized object containing a macroscopic fraction of the total energy of the
lattice. The initial-energy-density dependences of all characteristic time
scales of the soliton formation and merging are described analytically. Spatial
power spectra are computed and used for the quantitative explanation of the
numerical results.Comment: 12 pages, 7 figure
On a simple model of the photonic or phononic crystal
A model is proposed for a one-dimensional dielectric or elastic superlattice (SL) that relatively simply describes the frequency spectrum of electromagnetic or acoustic waves. The band frequency spectrum is reduced to mini-bands contracting with increasing frequency. A procedure is suggested for obtaining local states near a defect in a SL, and the simplest of these states is described. Conditions for the initiation of Bloch oscillations of a wave packet in a SL are discussed
Formation of soliton complexes in dispersive systems
The concept of soliton complex in a nonlinear dispersive medium is formulated. It is shown that interacting identical topological solitons in the
medium can form bound soliton complexes which move without radiation.
This phenomenon is considered to be universal and applicable to various physical systems. The soliton complex and its “excited” states are described analytically and numerically as solutions of nonlinear dispersive
equations with the fourth and higher order spatial or mixed derivatives.
The dispersive sine-Gordon, double and triple sine-Gordon, and piecewise
models are studied in detail. Mechanisms and conditions of the formation
of soliton complexes, and peculiarities of their stationary dynamics are investigated. A phenomenological approach to the description of the complexes and the classification of all the possible complex states are proposed. Some examples of physical systems, where the phenomenon can
be experimentally observed, are briefly discussed.Формулюється концепція солітонних комплексів в нелінійному дисперсійному середовищі. Показано, що взаємодіючі тотожні топологічні солітони у такому середовищі здатні утворювати солітонні комплекси, що рухаються без випромінювання. Вважається, що це явище є універсальним і зустрічається у різних фізичних системах. Солітонні комплекси і їхні збуджені стани описуються аналітично і чисельно як розв’язки нелінійних дисперсійних рівнянь з четвертою і
вищими просторовимі і змішаними похідними. Ретельно вивчаються дисперсійні системи синус-Гордон, подвійний і потрійний синус-Гордон, а також кусково-лінійна модель. Досліджуються механізми і
умови формування солітонних комплексів і особливості їхньої стаціонарної динаміки. Запропоновано феноменологічний підхід до описання комплексів і класифікацію усіх можливих їхніх станів. Стисло
розглянуті кілька прикладів фізичних систем, в яких це явище може
експериментально спостерігатись
Quantum carpet interferometry for trapped atomic Bose-Einstein condensates
We propose an ``interferometric'' scheme for Bose-Einstein condensates using
near-field diffraction. The scheme is based on the phenomenon of intermode
traces or quantum carpets; we show how it may be used in the detection of weak
forces.Comment: 4 figures. Submitted to Phys. Rev.
Some mechanisms of "spontaneous" polarization of superfluid He-4
Previously, a quantum "tidal" mechanism of polarization of the atoms of He-II
was proposed, according to which, as a result of interatomic interaction, each
atom of He-II acquires small fluctuating dipole and multipole moments, oriented
chaotically on the average. In this work, we show that, in the presence of a
temperature or density gradient in He-II, the originally chaotically oriented
tidal dipole moments of the atoms become partially ordered, which results in
volume polarization of He-II. It is found that the gravitational field of the
Earth induces electric induction U =10(-7)V in He-II (for vessel dimensions of
the order of 10 cm). We study also the connection of polarization and
acceleration, and discuss a possible nature of the electric signal dU = kdT/2e
observed by A.S. Rybalko in experiments with second sound.Comment: 13 pages; the calculation is extended and refined; v4: reconstructio
Evolution of discrete local levels into an impurity band in solidified inert gas solution
The density of states g(w) of disordered solutions of solidified inert gases have been calculated using the
Jacobian matrix method. The transformation of a discrete vibrational level into an impurity zone at a
growing concentration of light impurity atoms has been investigated. It is shown that a 1–10% change in the
impurity concentration leads to smearing the local discrete level into an impurity band. As this occurs,
additional resonance levels appear which carry important information about the impurity–impurity and impurity–
basic lattice force interactions in such solutions
Low Temperature Static and Dynamic Behavior of the Two-Dimensional Easy-Axis Heisenberg Model
We apply the self-consistent harmonic approximation (SCHA) to study static
and dynamic properties of the two-dimensional classical Heisenberg model with
easy-axis anisotropy. The static properties obtained are magnetization and spin
wave energy as functions of temperature, and the critical temperature as a
function of the easy-axis anisotropy. We also calculate the dynamic correlation
functions using the SCHA renormalized spin wave energy. Our analytical results,
for both static properties and dynamic correlation functions, are compared to
numerical simulation data combining cluster-Monte Carlo algorithms and Spin
Dynamics. The comparison allows us to conclude that far below the transition
temperature, where the SCHA is valid, spin waves are responsible for all
relevant features observed in the numerical simulation data; topological
excitations do not seem to contribute appreciably. For temperatures closer to
the transition temperature, there are differences between the dynamic
correlation functions from SCHA theory and Spin Dynamics; these may be due to
the presence of domain walls and solitons.Comment: 12 pages, 14 figure
Elementary excitations in one-dimensional spin-orbital models: neutral and charged solitons and their bound states
We study, both numerically and variationally, the interplay between different
types of elementary excitations in the model of a spin chain with anisotropic
spin-orbit coupling, in the vicinity of the "dimer line" with an exactly known
dimerized ground state. Our variational treatment is found to be in a
qualitative agreement with the exact diagonalization results. Soliton pairs are
shown to be the lowest excitations only in a very narrow region of the phase
diagram near the dimer line, and the phase transitions are always governed by
magnon-type excitations which can be viewed as soliton-antisoliton bound
states. It is shown that when the anisotropy exceeds certain critical value, a
new phase boundary appears. In the doped model on the dimer line, the exact
elementary charge excitation is shown to be a hole bound to a soliton. Bound
states of those "charged solitons" are studied; exact solutions for N-hole
bound states are presented.Comment: 11 pages revtex, 6 figure
Directed motion of domain walls in biaxial ferromagnets under the influence of periodic external magnetic fields
Directed motion of domain walls (DWs) in a classical biaxial ferromagnet
placed under the influence of periodic unbiased external magnetic fields is
investigated. Using the symmetry approach developed in this article the
necessary conditions for the directed DW motion are found. This motion turns
out to be possible if the magnetic field is applied along the most easy axis.
The symmetry approach prohibits the directed DW motion if the magnetic field is
applied along any of the hard axes. With the help of the soliton perturbation
theory and numerical simulations, the average DW velocity as a function of
different system parameters such as damping constant, amplitude, and frequency
of the external field, is computed.Comment: Added references, corrected typos, extended introductio
Glide and Superclimb of Dislocations in Solid He
Glide and climb of quantum dislocations under finite external stress,
variation of chemical potential and bias (geometrical slanting) in Peierls
potential are studied by Monte Carlo simulations of the effective string model.
We treat on unified ground quantum effects at finite temperatures . Climb at
low is assisted by superflow along dislocation core -- {\it superclimb}.
Above some critical stress avalanche-type creation of kinks is found. It is
characterized by hysteretic behavior at low . At finite biases gliding
dislocation remains rough even at lowest -- the behavior opposite to
non-slanted dislocations. In contrast to glide, superclimb is characterized by
quantum smooth state at low temperatures even for finite bias. In some
intermediate -range giant values of the compressibility as well as
non-Luttinger type behavior of the core superfluid are observed.Comment: Updated version submitted to JLTP as QFS2010 proceedings; 11 pages, 6
figure
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