566 research outputs found
A simple spin model for three steps relaxation and secondary proccesses in glass formers
A number of general trends are known to occur in systems displaying secondary
processes in glasses and glass formers. Universal features can be identified as
components of large and small cooperativeness whose competition leads to excess
wings or apart peaks in the susceptibility spectrum. To the aim of
understanding such rich and complex phenomenology we analyze the behavior of a
model combining two apart glassy components with a tunable different
cooperativeness. The model salient feature is, indeed, based on the competition
of the energetic contribution of groups of dynamically relevant variables,
e.g., density fluctuations, interacting in small and large sets. We investigate
how the model is able to reproduce the secondary processes physics without
further ad hoc ingredients, displaying known trends and properties under
cooling or pressing.Comment: 11 Pages, 11 Figure
Reply to Comment on ``Spherical 2+p spin-glass model: an analytically solvable model with a glass-to-glass transition''
In his Comment, Krakoviack [Phys. Rev. B (2007)] finds that the phase
behavior of the s+p spin-glass model is different from what proposed by
Crisanti and Leuzzi [Phys. Rev. B 73, 014412 (2006)] if s and p are larger than
two and are separated well enough. He proposes a trial picture, based on a one
step replica symmetry breaking solution, displaying a mode-coupling-like
glass-to-glass transition line ending in a A3 singularity. However, actually,
the physics of these systems changes when p-s is large, the instability of
which the one step replica symmetry breaking glassy phase suffers turns out to
be so wide ranging that the whole scenario proposed by Krakoviack must be
seriously reconsidered.Comment: 4 pages, 5 figure; reply to arXiv:0705.3187. To be published in Phys
Rev B 76 (2007
The K-sat problem in a simple limit
We compute the thermodynamic properties of the 3-satisfiability problem in
the infinite connectivity limit. In this limit the computations can be strongly
simplified and the thermodynamical properties can be obtained with an high
accuracy. We find evidence for a continuous replica symmetry breaking in the
region of high number of clauses, .Comment: 9 pages, 6 figures. To appear in J. Stat. Phys. Minor change
The disordered Backgammon model
In this paper we consider an exactly solvable model which displays glassy
behavior at zero temperature due to entropic barriers. The new ingredient of
the model is the existence of different energy scales or modes associated to
different relaxational time-scales. Low-temperature relaxation takes place by
partial equilibration of successive lower energy modes. An adiabatic scaling
solution, defined in terms of a threshold energy scale \eps^*, is proposed.
For such a solution, modes with energy \eps\gg\eps^* are equilibrated at the
bath temperature, modes with \eps\ll\eps^* remain out of equilibrium and
relaxation occurs in the neighborhood of the threshold \eps\sim \eps^*. The
model is presented as a toy example to investigate conditions related to the
existence of an effective temperature in glassy systems and its possible
dependence on the energy sector probed by the corresponding observable.Comment: 24 pages, 11 figure
The Complexity of the Spherical -spin spin glass model, revisited
Some questions concerning the calculation of the number of ``physical''
(metastable) states or complexity of the spherical -spin spin glass model
are reviewed and examined further. Particular attention is focused on the
general calculation procedure which is discussed step-by-step.Comment: 13 pages, 3 figure
The random Blume-Capel model on cubic lattice: first order inverse freezing in a 3D spin-glass system
We present a numerical study of the Blume-Capel model with quenched disorder
in 3D. The phase diagram is characterized by spin-glass/paramagnet phase
transitions of both first and second order in the thermodynamic sense.
Numerical simulations are performed using the Exchange-Monte Carlo algorithm,
providing clear evidence for inverse freezing. The main features at criticality
and in the phase coexistence region are investigated. The whole inverse
freezing transition appears to be first order. The second order transition
appears to be in the same universality class of the Edwards-Anderson model. The
nature of the spin-glass phase is analyzed by means of the finite size scaling
behavior of the overlap distribution functions and the four-spins real-space
correlation functions. Evidence for a replica symmetry breaking-like
organization of states is provided.Comment: 18 pages, 24 figures, 7 table
Complexity of the Sherrington-Kirkpatrick Model in the Annealed Approximation
A careful critical analysis of the complexity, at the annealed level, of the
Sherrington-Kirkpatrick model has been performed. The complexity functional is
proved to be always invariant under the Becchi-Rouet-Stora-Tyutin
supersymmetry, disregarding the formulation used to define it. We consider two
different saddle points of such functional, one satisfying the supersymmetry
[A. Cavagna {\it et al.}, J. Phys. A {\bf 36} (2003) 1175] and the other one
breaking it [A.J. Bray and M.A. Moore, J. Phys. C {\bf 13} (1980) L469]. We
review the previews studies on the subject, linking different perspectives and
pointing out some inadequacies and even inconsistencies in both solutions.Comment: 20 pages, 4 figure
Phase diagram and complexity of mode-locked lasers: from order to disorder
We investigate mode-locking processes in lasers displaying a variable degree
of structural randomness, from standard optical cavities to multiple-scattering
media. By employing methods mutuated from spin-glass theory, we analyze the
mean-field Hamiltonian and derive a phase-diagram in terms of the pumping rate
and the degree of disorder. Three phases are found: i) paramagnetic,
corresponding to a noisy continuous wave emission, ii) ferromagnetic, that
describes the standard passive mode-locking, and iii) the spin-glass in which
the phases of the electromagnetic field are frozen in a exponentially large
number of configurations. The way the mode-locking threshold is affected by the
amount of disorder is quantified. The results are also relevant for other
physical systems displaying a random Hamiltonian, like Bose-Einstein
condensates and nonlinear optical beams.Comment: 4 pages, 2 figure
The Ising M-p-spin mean-field model for the structural glass: continuous vs. discontinuous transition
The critical behavior of a family of fully connected mean-field models with
quenched disorder, the Ising spin glass, is analyzed, displaying a
crossover between a continuous and a random first order phase transition as a
control parameter is tuned. Due to its microscopic properties the model is
straightforwardly extendable to finite dimensions in any geometry.Comment: 10 pages, 1 figure, 1 tabl
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