65 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
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 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
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
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
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
Influence of exciton spin relaxation on the photoluminescence spectra of semimagnetic quantum dots
We present a comprehensive experimental and theoretical studies of
photoluminescence of single CdMnTe quantum dots with Mn content x ranging from
0.01 to 0.2. We distinguish three stages of the equilibration of the exciton-Mn
ion spin system and show that the intermediate stage, in which the exciton spin
is relaxed, while the total equilibrium is not attained, gives rise to a
specific asymmetric shape of the photoluminescence spectrum. From an excellent
agreement between the measured and calculated spectra we are able to evaluate
the exciton localization volume, number of paramagnetic Mn ions, and their
temperature for each particular dot. We discuss the values of these parameters
and compare them with results of other experiments. Furthermore, we analyze the
dependence of average Zeeman shifts and transition linewidths on the Mn content
and point out specific processes, which control these values at particular Mn
concentrations.Comment: submitted to Phys. Rev.
The nature of slow dynamics in a minimal model of frustration-limited domains
We present simulation results for the dynamics of a schematic model based on
the frustration-limited domain picture of glass-forming liquids. These results
are compared with approximate theoretical predictions analogous to those
commonly used for supercooled liquid dynamics. Although model relaxation times
increase by several orders of magnitude in a non-Arrhenius manner as a
microphase separation transition is approached, the slow relaxation is in many
ways dissimilar to that of a liquid. In particular, structural relaxation is
nearly exponential in time at each wave vector, indicating that the mode
coupling effects dominating liquid relaxation are comparatively weak within
this model. Relaxation properties of the model are instead well reproduced by
the simplest dynamical extension of a static Hartree approximation. This
approach is qualitatively accurate even for temperatures at which the mode
coupling approximation predicts loss of ergodicity. These results suggest that
the thermodynamically disordered phase of such a minimal model poorly
caricatures the slow dynamics of a liquid near its glass transition
A Monte Carlo study of the three-dimensional Coulomb frustrated Ising ferromagnet
We have investigated by Monte-Carlo simulation the phase diagram of a
three-dimensional Ising model with nearest-neighbor ferromagnetic interactions
and small, but long-range (Coulombic) antiferromagnetic interactions. We have
developed an efficient cluster algorithm and used different lattice sizes and
geometries, which allows us to obtain the main characteristics of the
temperature-frustration phase diagram. Our finite-size scaling analysis
confirms that the melting of the lamellar phases into the paramgnetic phase is
driven first-order by the fluctuations. Transitions between ordered phases with
different modulation patterns is observed in some regions of the diagram, in
agreement with a recent mean-field analysis.Comment: 14 pages, 10 figures, submitted to Phys. Rev.
Dynamics of systems with isotropic competing interactions in an external field: a Langevin approach
We study the Langevin dynamics of a ferromagnetic Ginzburg-Landau Hamiltonian
with a competing long-range repulsive term in the presence of an external
magnetic field. The model is analytically solved within the self consistent
Hartree approximation for two different initial conditions: disordered or zero
field cooled (ZFC), and fully magnetized or field cooled (FC). To test the
predictions of the approximation we develop a suitable numerical scheme to
ensure the isotropic nature of the interactions. Both the analytical approach
and the numerical simulations of two-dimensional finite systems confirm a
simple aging scenario at zero temperature and zero field. At zero temperature a
critical field is found below which the initial conditions are relevant
for the long time dynamics of the system. For a logarithmic growth of
modulated domains is found in the numerical simulations but this behavior is
not captured by the analytical approach which predicts a growth law at
- âŠ