79 research outputs found
Gibbs attractor: a chaotic nearly Hamiltonian system, driven by external harmonic force
A chaotic autonomous Hamiltonian systems, perturbed by small damping and
small external force, harmonically dependent on time, can acquire a strange
attractor with properties similar to that of the canonical distribution - the
Gibbs attractor. The evolution of the energy in such systems can be described
as the energy diffusion. For the nonlinear Pullen - Edmonds oscillator with two
degrees of freedom the properties of the Gibbs attractor and their dependence
on parameters of the perturbation are studied both analytically and
numerically.Comment: 8 pages RevTeX, 3 figure
A pulsed atomic soliton laser
It is shown that simultaneously changing the scattering length of an
elongated, harmonically trapped Bose-Einstein condensate from positive to
negative and inverting the axial portion of the trap, so that it becomes
expulsive, results in a train of self-coherent solitonic pulses. Each pulse is
itself a non-dispersive attractive Bose-Einstein condensate that rapidly
self-cools. The axial trap functions as a waveguide. The solitons can be made
robustly stable with the right choice of trap geometry, number of atoms, and
interaction strength. Theoretical and numerical evidence suggests that such a
pulsed atomic soliton laser can be made in present experiments.Comment: 11 pages, 4 figure
On the interaction of a single-photon wave packet with an excited atom
The interaction of a single-photon wave packet with an initially excited
two-level atom in free space is studied in semiclassical and quantum
approaches. It is shown that the final state of the field does not contain
doubly occupied modes. The process of the atom's transition to the ground state
may be accelerated, decelerated or even reversed by the incoming photon,
depending on parameters. The spectrum of emitted radiation is close to the sum
of the spectrum of the incoming single-photon wave packet and the natural line
shape, with small and complicated deviations.Comment: 17 pages, 5 figure
Pseudogap in 1d revisited
Two decades ago, Sadovskii found an exact solution of a model describing a
pseudogap in electron energy spectrum (first introduced by Lee, Rice and
Anderson). The discovery of a pseudogap in high-Tc superconductors has revived
the interest to his exact solution. I review the model with the emphasis on
physical content, point out an error in the original Sadovskii's solution and
explain which problem he actually solved. A recent incorporation of Sadovskii's
ideas into a description of "hot spots" on the Fermi surface in cuprate
superconductors (Schmalian, Pines and Stojkovic) is briefly discussed.Comment: Final version to appear in PR
The dynamics of a strongly driven two component Bose-Einstein Condensate
We consider a two component Bose-Einstein condensate in two spatially
localized modes of a double well potential, with periodic modulation of the
tunnel coupling between the two modes. We treat the driven quantum field using
a two mode expansion and define the quantum dynamics in terms of the Floquet
Operator for the time periodic Hamiltonian of the system. It has been shown
that the corresponding semiclassical mean-field dynamics can exhibit regions of
regular and chaotic motion. We show here that the quantum dynamics can exhibit
dynamical tunneling between regions of regular motion, centered on fixed points
(resonances) of the semiclassical dynamics
Microscopic theory of weak pseudogap behavior in the underdoped cuprate superconductors I: General theory and quasiparticle properties
We derive in detail a novel solution of the spin fermion model which is valid
in the quasi-static limit pi T<<omega_sf, found in the intermediate
(pseudoscaling) regime of the magnetic phase diagram of cuprate
superconductors, and use it to obtain results for the temperature and doping
dependence of the single particle spectral density, the electron-spin
fluctuation vertex function, and the low frequency dynamical spin
susceptibility. The resulting strong anisotropy of the spectral density and the
vertex function lead to the qualitatively different behavior of_hot_ (around
k=(pi,0)) and_cold_ (around k=(pi/2,pi/2)) quasiparticles seen in ARPES
experiments. We find that the broad high energy features found in ARPES
measurements of the spectral density of the underdoped cuprate superconductors
are determined by strong antiferromagnetic (AF) correlations and incoherent
precursor effects of an SDW state, with reduced renormalized effective coupling
constant. The electron spin-fluctuation vertex function, i.e. the effective
interaction of low energy quasiparticles and spin degrees of freedom, is found
to be strongly anisotropic and enhanced for hot quasiparticles; the
corresponding charge-fluctuation vertex is considerably diminished. We thus
demonstrate that, once established, strong AF correlations act to reduce
substantially the effective electron-phonon coupling constant in cuprate
superconductors.Comment: REVTEX with EPS figures, uses multicol.sty, epsfig,sty, psfig.st
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