28 research outputs found
Microchemistry-dependent simulation of yield stress and flow stress in non-heat treatable Al sheet alloys
Spreading, Nonergodicity, and Selftrapping: a puzzle of interacting disordered lattice waves
Localization of waves by disorder is a fundamental physical problem
encompassing a diverse spectrum of theoretical, experimental and numerical
studies in the context of metal-insulator transitions, the quantum Hall effect,
light propagation in photonic crystals, and dynamics of ultra-cold atoms in
optical arrays, to name just a few examples. Large intensity light can induce
nonlinear response, ultracold atomic gases can be tuned into an interacting
regime, which leads again to nonlinear wave equations on a mean field level.
The interplay between disorder and nonlinearity, their localizing and
delocalizing effects is currently an intriguing and challenging issue in the
field of lattice waves. In particular it leads to the prediction and
observation of two different regimes of destruction of Anderson localization -
asymptotic weak chaos, and intermediate strong chaos, separated by a crossover
condition on densities. On the other side approximate full quantum interacting
many body treatments were recently used to predict and obtain a novel many body
localization transition, and two distinct phases - a localization phase, and a
delocalization phase, both again separated by some typical density scale. We
will discuss selftrapping, nonergodicity and nonGibbsean phases which are
typical for such discrete models with particle number conservation and their
relation to the above crossover and transition physics. We will also discuss
potential connections to quantum many body theories.Comment: 13 pages in Springer International Publishing Switzerland 2016 1 M.
Tlidi and M. G. Clerc (eds.), Nonlinear Dynamics: Materials, Theory and
Experiment, Springer Proceedings in Physics 173. arXiv admin note: text
overlap with arXiv:1405.112
Wave interactions in localizing media - a coin with many faces
A variety of heterogeneous potentials are capable of localizing linear
non-interacting waves. In this work, we review different examples of
heterogeneous localizing potentials which were realized in experiments. We then
discuss the impact of nonlinearity induced by wave interactions, in particular
its destructive effect on the localizing properties of the heterogeneous
potentials.Comment: Review submitted to Intl. Journal of Bifurcation and Chaos Special
Issue edited by G. Nicolis, M. Robnik, V. Rothos and Ch. Skokos 21 Pages, 8
Figure
Nonlinear Lattice Waves in Random Potentials
Localization of waves by disorder is a fundamental physical problem
encompassing a diverse spectrum of theoretical, experimental and numerical
studies in the context of metal-insulator transition, quantum Hall effect,
light propagation in photonic crystals, and dynamics of ultra-cold atoms in
optical arrays. Large intensity light can induce nonlinear response, ultracold
atomic gases can be tuned into an interacting regime, which leads again to
nonlinear wave equations on a mean field level. The interplay between disorder
and nonlinearity, their localizing and delocalizing effects is currently an
intriguing and challenging issue in the field. We will discuss recent advances
in the dynamics of nonlinear lattice waves in random potentials. In the absence
of nonlinear terms in the wave equations, Anderson localization is leading to a
halt of wave packet spreading.
Nonlinearity couples localized eigenstates and, potentially, enables
spreading and destruction of Anderson localization due to nonintegrability,
chaos and decoherence. The spreading process is characterized by universal
subdiffusive laws due to nonlinear diffusion. We review extensive computational
studies for one- and two-dimensional systems with tunable nonlinearity power.
We also briefly discuss extensions to other cases where the linear wave
equation features localization: Aubry-Andre localization with quasiperiodic
potentials, Wannier-Stark localization with dc fields, and dynamical
localization in momentum space with kicked rotors.Comment: 45 pages, 19 figure
Interactions destroy dynamical localization with strong and weak chaos
Bose-Einstein condensates loaded into kicked optical lattices can be treated
as quantum kicked rotor systems. Noninteracting rotors show dynamical
localization in momentum space. The experimentally tunable condensate
interaction is included in a qualitative Gross-Pitaevskii type model based on
two-body interactions. We observe strong and weak chaos regimes of wave packet
spreading in momentum space. In the intermediate strong chaos regime the
condensate energy grows as . In the asymptotic weak chaos case the
growth crosses over into a law. The results do not depend on the
details of the kicking.Comment: 6 pages, 3 figures, submitted to Europhys. Let
Thermal conductivity of nonlinear waves in disordered chains
We present computational data on the thermal conductivity of nonlinear waves
in disordered chains. Disorder induces Anderson localization for linear waves
and results in a vanishing conductivity. Cubic nonlinearity restores normal
conductivity, but with a strongly temperature-dependent conductivity
. We find indications for an asymptotic low-temperature and intermediate temperature laws. These findings are in
accord with theoretical studies of wave packet spreading, where a regime of
strong chaos is found to be intermediate, followed by an asymptotic regime of
weak chaos (EPL 91 (2010) 30001).Comment: 8 pages, 3 figure
Strong and weak chaos in weakly nonintegrable many-body Hamiltonian systems
We study properties of chaos in generic one-dimensional nonlinear Hamiltonian
lattices comprised of weakly coupled nonlinear oscillators, by numerical
simulations of continuous-time systems and symplectic maps. For small coupling,
the measure of chaos is found to be proportional to the coupling strength and
lattice length, with the typical maximal Lyapunov exponent being proportional
to the square root of coupling. This strong chaos appears as a result of
triplet resonances between nearby modes. In addition to strong chaos we observe
a weakly chaotic component having much smaller Lyapunov exponent, the measure
of which drops approximately as a square of the coupling strength down to
smallest couplings we were able to reach. We argue that this weak chaos is
linked to the regime of fast Arnold diffusion discussed by Chirikov and
Vecheslavov. In disordered lattices of large size we find a subdiffusive
spreading of initially localized wave packets over larger and larger number of
modes. The relations between the exponent of this spreading and the exponent in
the dependence of the fast Arnold diffusion on coupling strength are analyzed.
We also trace parallels between the slow spreading of chaos and deterministic
rheology.Comment: 15 pages, 14 figure
Kolmogorov turbulence, Anderson localization and KAM integrability
The conditions for emergence of Kolmogorov turbulence, and related weak wave
turbulence, in finite size systems are analyzed by analytical methods and
numerical simulations of simple models. The analogy between Kolmogorov energy
flow from large to small spacial scales and conductivity in disordered solid
state systems is proposed. It is argued that the Anderson localization can stop
such an energy flow. The effects of nonlinear wave interactions on such a
localization are analyzed. The results obtained for finite size system models
show the existence of an effective chaos border between the
Kolmogorov-Arnold-Moser (KAM) integrability at weak nonlinearity, when energy
does not flow to small scales, and developed chaos regime emerging above this
border with the Kolmogorov turbulent energy flow from large to small scales.Comment: 8 pages, 6 figs, EPJB style
The Nonlinear Schroedinger Equation with a random potential: Results and Puzzles
The Nonlinear Schroedinger Equation (NLSE) with a random potential is
motivated by experiments in optics and in atom optics and is a paradigm for the
competition between the randomness and nonlinearity. The analysis of the NLSE
with a random (Anderson like) potential has been done at various levels of
control: numerical, analytical and rigorous. Yet, this model equation presents
us with a highly inconclusive and often contradictory picture. We will describe
the main recent results obtained in this field and propose a list of specific
problems to focus on, that we hope will enable to resolve these outstanding
questions.Comment: 21 pages, 4 figure