170 research outputs found
Comment on ``Stripe Glasses: Self-Generated Randomness in a Uniformly Frustrated System''
comment on J. Schmalian and P. Wolynes, Phys. Rev. Lett. {\bf 85}, 836
(2000).Comment: 1 page, 1 Figure, accepted in Phys. Rev. Letter
Non glassy ground-state in a long-range antiferromagnetic frustrated model in the hypercubic cell
We analize the statistical mechanics of a long-range antiferromagnetic model
defined on a D-dimensional hypercube, both at zero and finite temperatures. The
associated Hamiltonian is derived from a recently proposed complexity measure
of Boolean functions, in the context of neural networks learning processes. We
show that, depending of the value of D, the system either presents a low
temperature antiferromagnetic stable phase or the global antiferromagnetic
order disappears at any temperature. In the last case the ground state is an
infinitely degenerated non-glassy one, composed by two equal size anti-aligned
antiferromagnetic domains. We also present some results for the ferromagnetic
version of the model.Comment: 8 pages, 5 figure
Langevin dynamics of the Coulomb frustrated ferromagnet: a mode-coupling analysis
We study the Langevin dynamics of the soft-spin, continuum version of the
Coulomb frustrated Ising ferromagnet. By using the dynamical mode-coupling
approximation, supplemented by reasonable approximations for describing the
equilibrium static correlation function, and the somewhat improved dynamical
self-consistent screening approximation, we find that the system displays a
transition from an ergodic to a non-ergodic behavior. This transition is
similar to that obtained in the idealized mode-coupling theory of glassforming
liquids and in the mean-field generalized spin glasses with one-step replica
symmetry breaking. The significance of this result and the relation to the
appearance of a complex free-energy landscape are also discussed.Comment: 13 pages, 11 figures, submitted to Phys. Rev.
Evidence of polariton induced transparency in a single organic quantum wire
The resonant interaction between quasi-one dimensional excitons and photons
is investigated. For a single isolated organic quantum wire, embedded in its
single crystal monomer matrix, the strong exciton-photon coupling regime is
reached. This is evidenced by the suppression of the resonant excitonic
absorption arising when the system eigenstate is a polariton. These
observations demonstrate that the resonant excitonic absorption in a
semiconductor can be understood in terms of a balance between the exciton
coherence time and the Rabi period between exciton-like and photon-like states
of the polariton.Comment: 9 pages and 4 figure
Evidence for "fragile" glass-forming behavior in the relaxation of Coulomb frustrated three-dimensional systems
We show by means of a Monte Carlo simulation study that three-dimensional
models with long-range frustration display the generic phenomena seen in
fragile glassforming liquids. Due to their properties (absence of quenched
disorder, physical motivation in terms of structural frustration, and tunable
fragility), these systems appear as promising minimal theoretical models for
describing the glass transition of supercooled liquids.Comment: 4 pages, 4 figure
Microphase Separation and modulated phases in a Coulomb frustrated Ising ferromagnet
We study a 3-dimensional Ising model in which the tendency to order due to
short-range ferromagnetic interactions is frustrated by competing long-range
(Coulombic) interactions. Complete ferromagnetic ordering is impossible for any
nonzero value of the frustration parameter, but the system displays a variety
of phases characterized by periodically modulated structures. We have performed
extensive Monte-Carlo simulations which provide strong evidence that the
microphase separation transition between paramagnetic and modulated phases is a
fluctuation-induced first-order transition. Additional transitions to various
commensurate phases may also occur when further lowering the temperature.Comment: 6 pages, 4 figures, accepted in Europhys. Letter
The frustrated spherical model: an alternative to Ginzburg-Landau Hamiltonians with competing interactions
We solve analytically the Langevin dynamics of the classic spherical model
considering the ferromagnetic exchange and a long-range antiferromagnetic
interaction. Our results in the asymptotic regime, shows an equivalence in the
functionality of the spatial and self-correlations between this model and the
recently studied Ginzburg-Landau frustrated model within the Hartree
approximation. A careful discussion is done about the low temperature behavior
in the context of glassy dynamics. The appearance of interesting features
regarding the establishment of the ferromagnetic phase is also analyzed in view
of the effects of the spherical restriction. We propose a new variant of the
spherical model in which the global restriction is substituted by an infinite
set of restrictions over finite size regions. This modification leads to a new
dynamical equation that suggests the appearance of the low temperature phase
transition even in the non-frustrated case were the classic spherical model
fails
Etude de la variabilité d'un agent pathogène, Xanthomonas campestris pv manihotis, par l'analyse factorielle multiple
International audienc
Locally Preferred Structure and Frustration in Glassforming Liquids: A Clue to Polyamorphism?
We propose that the concept of liquids characterized by a given locally
preferred structure (LPS) could help in understanding the observed phenomenon
of polyamorphism. ``True polyamorphism'' would involve the competition between
two (or more) distinct LPS, one favored at low pressure because of its low
energy and one favored at high pressure because of its small specific volume,
as in tetrahedrally coordinated systems. ``Apparent polyamorphism'' could be
associated with the existence of a poorly crystallized defect-ordered phase
with a large unit cell and small crystallites, which may be illustrated by the
metastable glacial phase of the fragile glassformer triphenylphosphite; the
apparent polyamorphism might result from structural frustration, i. e., a
competition between the tendency to extend the LPS and a global constraint that
prevents tiling of the whole space by the LPS.Comment: 11, 6 figures, Proceedings of the Conference "Horizons in Complex
Systems", Messina; in honor of the 60th birthday of H.E. Stanle
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