1,768 research outputs found
Obtaining Breathers in Nonlinear Hamiltonian Lattices
We present a numerical method for obtaining high-accuracy numerical solutions
of spatially localized time-periodic excitations on a nonlinear Hamiltonian
lattice. We compare these results with analytical considerations of the spatial
decay. We show that nonlinear contributions have to be considered, and obtain
very good agreement between the latter and the numerical results. We discuss
further applications of the method and results.Comment: 21 pages (LaTeX), 8 figures in ps-files, tar-compressed uuencoded
file, Physical Review E, in pres
Breathers on lattices with long range interaction
We analyze the properties of breathers (time periodic spatially localized
solutions) on chains in the presence of algebraically decaying interactions
. We find that the spatial decay of a breather shows a crossover from
exponential (short distances) to algebraic (large distances) decay. We
calculate the crossover distance as a function of and the energy of the
breather. Next we show that the results on energy thresholds obtained for short
range interactions remain valid for and that for (anomalous
dispersion at the band edge) nonzero thresholds occur for cases where the short
range interaction system would yield zero threshold values.Comment: 4 pages, 2 figures, PRB Rapid Comm. October 199
Dynamical mechanisms of DC current generation in driven Hamiltonian systems
Recent symmetry considerations (Phys. Rev. Lett. {\bf 84} 2358 (2000)) have
shown that dc currents may be generated in the stochastic layer of a system
describing the motion of a particle in a one-dimensional potential in the
presence of an ac time-periodic drive. In this paper we explain the dynamical
origin of this current. We show that the dc current is induced by the presence
and desymmetrization of ballistic channels inside the stochastic layer. The
existence of these channels is due to resonance islands with non-zero winding
numbers. The characterization of the flights dynamics inside ballistic channels
is described by distribution functions. We obtain these distribution functions
numerically and find very good agreement with simulation data.Comment: 4 pages, 3 figure
AC-driven quantum spins: resonant enhancement of transverse DC magnetization
We consider s=1/2 spins in the presence of a constant magnetic field in
z-direction and an AC magnetic field in the x-z plane. A nonzero DC
magnetization component in y direction is a result of broken symmetries. A
pairwise interaction between two spins is shown to resonantly increase the
induced magnetization by one order of magnitude. We discuss the mechanism of
this enhancement, which is due to additional avoided crossings in the level
structure of the system.Comment: 7 pages, 7 figure
Interaction of discrete breathers with electrons in nonlinear lattices
We study the effects of electron-lattice interaction in the presence of
discrete breathers. The lattice is treated classically. We consider two
different situations - i) the scattering of an electron by a discrete breather
in the semiconducting regime, where the electron-breather distance is large
compared to the breather size, and ii) the appearance of a bound
electron-breather state, which exists at least over one half of the breather
period of oscillation. In the second case the localization length of the
electron can be of the order of the breather size - a few lattice periods.
Remarkably these results are derived in the absence of disorder, since discrete
breathers exist in translationally invariant nonlinear lattices
Spreading of wave packets in disordered systems with tunable nonlinearity
We study the spreading of single-site excitations in one-dimensional
disordered Klein-Gordon chains with tunable nonlinearity for different values of . We perform extensive numerical
simulations where wave packets are evolved a) without and, b) with dephasing in
normal mode space. Subdiffusive spreading is observed with the second moment of
wave packets growing as . The dependence of the numerically
computed exponent on is in very good agreement with our
theoretical predictions both for the evolution of the wave packet with and
without dephasing (for in the latter case). We discuss evidence
of the existence of a regime of strong chaos, and observe destruction of
Anderson localization in the packet tails for small values of .Comment: 9 pages, 7 figure
Slow Relaxation and Phase Space Properties of a Conservative System with Many Degrees of Freedom
We study the one-dimensional discrete model. We compare two
equilibrium properties by use of molecular dynamics simulations: the Lyapunov
spectrum and the time dependence of local correlation functions. Both
properties imply the existence of a dynamical crossover of the system at the
same temperature. This correlation holds for two rather different regimes of
the system - the displacive and intermediate coupling regimes. Our results
imply a deep connection between slowing down of relaxations and phase space
properties of complex systems.Comment: 14 pages, LaTeX, 10 Figures available upon request (SF), Phys. Rev.
E, accepted for publicatio
Nonlinear response and discrete breather excitation in driven micro-mechanical cantilever arrays
We explain the origin of the generation of discrete breathers (DBs) in
experiments on damped and driven micromechanical cantilever arrays (M.Sato et
al. Phys. Rev. Lett. {\bf 90}, 044102, 2003). Using the concept of the
nonlinear response manifold (NLRM) we provide a systematic way to find the
optimal parameter regime in damped and driven lattices where DBs exist. Our
results show that DBs appear via a new instability of the NLRM different from
the anticipated modulational instability (MI) known for conservative systems.
We present several ways of exciting DBs, and compare also to experimental
studies of exciting and destroying DBs in antiferromagnetic layered systems.Comment: 4 pages, 5 figure
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