1,610 research outputs found
Directed transport and localization in phase-modulated driven lattices
We explore the dynamics of non-interacting particles loaded into a
phase-modulated one-dimensional lattice formed by laterally oscillating square
barriers. Tuning the parameters of the driven unit cell of the lattice selected
parts of the classical phase space can be manipulated in a controllable manner.
We find superdiffusion in position space for all parameters regimes. A directed
current of an ensemble of particles can be created through locally breaking the
spatiotemporal symmetries of the time-driven potential. Magnitude and direction
of the current are tunable. Several mechanisms for transient localization and
trapping of particles in different wells of the driven unit cell are presented
and analyzed
Pentaquarks with One Color Sextet Diquark
The masses of pentaquarks are calculated within the framework of
a semirelativistic effective QCD Hamiltonian, using a diquark picture. This
approximation allows a correct treatment of the confinement, assumed here to be
similar to a Y-junction. With only color antitriplet diquarks, the mass of the
pentaquark candidate with positive parity is found around 2.2 GeV. It
is shown that, if a color sextet diquark is present, the lowest
pentaquark is characterized by a much smaller mass with a negative parity. A
mass below 1.7 GeV is computed, if the masses of the color antitriplet and
color sextet diquarks are taken similar
Effect of pressure on the polarized infrared optical response of quasi-one-dimensional LaTiO
The pressure-induced changes in the optical properties of the
quasi-one-dimensional conductor LaTiO were studied by
polarization-dependent mid-infrared micro-spectroscopy at room temperature. For
the polarization of the incident radiation parallel to the conducting
direction, the optical conductivity spectrum shows a pronounced mid-infrared
absorption band, exhibiting a shift to lower frequencies and an increase in
oscillator strength with increasing pressure. On the basis of its pressure
dependence, interpretations of the band in terms of electronic transitions and
polaronic excitations are discussed. Discontinuous changes in the optical
response near 15 GPa are in agreement with a recently reported pressure-induced
structural phase transition and indicate the onset of a dimensional crossover
in this highly anisotropic system.Comment: 7 pages, 7 figure
Multifractal eigenstates of quantum chaos and the Thue-Morse sequence
We analyze certain eigenstates of the quantum baker's map and demonstrate,
using the Walsh-Hadamard transform, the emergence of the ubiquitous Thue-Morse
sequence, a simple sequence that is at the border between quasi-periodicity and
chaos, and hence is a good paradigm for quantum chaotic states. We show a
family of states that are also simply related to Thue-Morse sequence, and are
strongly scarred by short periodic orbits and their homoclinic excursions. We
give approximate expressions for these states and provide evidence that these
and other generic states are multifractal.Comment: Substantially modified from the original, worth a second download. To
appear in Phys. Rev. E as a Rapid Communicatio
Extreme events in discrete nonlinear lattices
We perform statistical analysis on discrete nonlinear waves generated though
modulational instability in the context of the Salerno model that interpolates
between the intergable Ablowitz-Ladik (AL) equation and the nonintegrable
discrete nonlinear Schrodinger (DNLS) equation. We focus on extreme events in
the form of discrete rogue or freak waves that may arise as a result of rapid
coalescence of discrete breathers or other nonlinear interaction processes. We
find power law dependence in the wave amplitude distribution accompanied by an
enhanced probability for freak events close to the integrable limit of the
equation. A characteristic peak in the extreme event probability appears that
is attributed to the onset of interaction of the discrete solitons of the AL
equation and the accompanied transition from the local to the global
stochasticity monitored through the positive Lyapunov exponent of a nonlinear
map.Comment: 5 pages, 4 figures; reference added, figure 2 correcte
Dynamical screening of the Coulomb interaction for two confined electrons in a magnetic field
We show that a difference in time scales of vertical and lateral dynamics
permits one to analyze the problem of interacting electrons confined in an
axially symmetric three-dimensional potential with a lateral oscillator
confinement by means of the effective two-dimensional Hamiltonian with a
screened Coulomb interaction. Using an adiabatic approximation based on
action-angle variables, we present solutions for the effective charge of the
Coulomb interaction (screening) for a vertical confinement potential simulated
by parabolic, square, and triangular wells. While for the parabolic potential
the solution for the effective charge is given in a closed anlytical form, for
the other cases similar solutions can be easily calculated numerically.Comment: 10 pages, 6 figure
Lyapunov exponents as a dynamical indicator of a phase transition
We study analytically the behavior of the largest Lyapunov exponent
for a one-dimensional chain of coupled nonlinear oscillators, by
combining the transfer integral method and a Riemannian geometry approach. We
apply the results to a simple model, proposed for the DNA denaturation, which
emphasizes a first order-like or second order phase transition depending on the
ratio of two length scales: this is an excellent model to characterize
as a dynamical indicator close to a phase transition.Comment: 8 Pages, 3 Figure
Mixing and reaction efficiency in closed domains
We present a numerical study of mixing and reaction efficiency in closed
domains. In particular we focus our attention on laminar flows. In the case of
inert transport the mixing properties of the flows strongly depend on the
details of the Lagrangian transport. We also study the reaction efficiency.
Starting with a little spot of product we compute the time needed to complete
the reaction in the container. We found that the reaction efficiency is not
strictly related to the mixing properties of the flow. In particular, reaction
acts as a "dynamical regulator".Comment: 11 pages, 10 figure
Superconvergent Perturbation Method in Quantum Mechanics
An analogue of Kolmogorov's superconvergent perturbation theory in classical
mechanics is constructed for self adjoint operators. It is different from the
usual Rayleigh--Schr\"odinger perturbation theory and yields expansions for
eigenvalues and eigenvectors in terms of functions of the perturbation
parameter.Comment: 11 pages, LaTe
Super-diffusion in optical realizations of Anderson localization
We discuss the dynamics of particles in one dimension in potentials that are
random both in space and in time. The results are applied to recent optics
experiments on Anderson localization, in which the transverse spreading of a
beam is suppressed by random fluctuations in the refractive index. If the
refractive index fluctuates along the direction of the paraxial propagation of
the beam, the localization is destroyed. We analyze this broken localization,
in terms of the spectral decomposition of the potential. When the potential has
a discrete spectrum, the spread is controlled by the overlap of Chirikov
resonances in phase space. As the number of Fourier components is increased,
the resonances merge into a continuum, which is described by a Fokker-Planck
equation. We express the diffusion coefficient in terms of the spectral
intensity of the potential. For a general class of potentials that are commonly
used in optics, the solutions of the Fokker-Planck equation exhibit anomalous
diffusion in phase space, implying that when Anderson localization is broken by
temporal fluctuations of the potential, the result is transport at a rate
similar to a ballistic one or even faster. For a class of potentials which
arise in some existing realizations of Anderson localization atypical behavior
is found.Comment: 11 pages, 2 figure
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