17,984 research outputs found
A discrete nonlinear model with substrate feedback
We consider a prototypical model in which a nonlinear field (continuum or
discrete) evolves on a flexible substrate which feeds back to the evolution of
the main field. We identify the underlying physics and potential applications
of such a model and examine its simplest one-dimensional Hamiltonian form,
which turns out to be a modified Frenkel-Kontorova model coupled to an extra
linear equation. We find static kink solutions and study their stability, and
then examine moving kinks (the continuum limit of the model is studied too). We
observe how the substrate effectively renormalizes properties of the kinks. In
particular, a nontrivial finding is that branches of stable and unstable kink
solutions may be extended beyond a critical point at which an effective
intersite coupling vanishes; passing this critical point does not destabilize
the kink. Kink-antikink collisions are also studied, demonstrating alternation
between merger and transmission cases.Comment: a revtex text file and 6 ps files with figures. Physical Review E, in
pres
Pairing in Inhomogeneous Superconductors
Starting from a t-J model, we introduce inhomogeneous terms to mimic stripes.
We find that if the inhomogeneous terms break the SU(2) spin symmetry the
binding between holes is tremendously enhanced in the thermodynamic limit. In
any other model (including homogeneous models) the binding in the thermodynamic
limit is small or neglible. By including these inhomogeneous terms we can
reproduce experimental neutron scattering data. We also discuss the connection
of the resulting inhomogeneity-induced superconductivity to recent experimental
evidence for a linear relation between magnetic incommensurability and the
superconducting transition temperature, as a function of doping.Comment: 4 pages, 2 figure
Discrete Breathers in a Nonlinear Polarizability Model of Ferroelectrics
We present a family of discrete breathers, which exists in a nonlinear
polarizability model of ferroelectric materials. The core-shell model is set up
in its non-dimensionalized Hamiltonian form and its linear spectrum is
examined. Subsequently, seeking localized solutions in the gap of the linear
spectrum, we establish that numerically exact and potentially stable discrete
breathers exist for a wide range of frequencies therein.
In addition, we present nonlinear normal mode, extended spatial profile
solutions from which the breathers bifurcate, as well as other associated
phenomena such as the formation of phantom breathers within the model.
The full bifurcation picture of the emergence and disappearance of the
breathers is complemented by direct numerical simulations of their dynamical
instability, when the latter arises.Comment: 9 pages, 7 figures, 1 tabl
Spectral signatures of the Luttinger liquid to charge-density-wave transition
Electron- and phonon spectral functions of the one-dimensional,
spinless-fermion Holstein model at half filling are calculated in the four
distinct regimes of the phase diagram, corresponding to an attractive or
repulsive Luttinger liquid at weak electron-phonon coupling, and a band- or
polaronic insulator at strong coupling. The results obtained by means of kernel
polynomial and systematic cluster approaches reveal substantially different
physics in these regimes and further indicate that the size of the phonon
frequency significantly affects the nature of the quantum Peierls phase
transition.Comment: 5 pages, 4 figures; final version, accepted for publication in
Physical Review
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