238 research outputs found
Fragile vs strong liquids: a saddles ruled scenario
In the context of the energy landscape description of supercooled liquids, we
propose an explanation for the different behaviour of fragile and strong
liquids. Above the Goldstein crossover temperature Tx, diffusion is interpreted
as a motion in the phase space among unstable stationary points of the
potential energy, that is among saddles. In this way two mechanisms of
diffusion arise: mechanism A takes place when the system crosses potential
energy barriers along stable uphill directions, while mechanism B consists in
finding unstable downhill directions out of a saddle. Depending on the mutual
value of the efficiency temperatures of A and B, we obtain two very different
behaviours of the viscosity, reproducing the usual classification of liquids in
fragile and strong. Moreover, this scenario very naturally predicts the
possibility of a fragile-to-strong crossover when lowering the temperature.Comment: Revised versio
Glass and polycrystal states in a lattice spin model
We numerically study a nondisordered lattice spin system with a first order
liquid-crystal transition, as a model for supercooled liquids and glasses.
Below the melting temperature the system can be kept in the metastable liquid
phase, and it displays a dynamic phenomenology analogous to fragile supercooled
liquids, with stretched exponential relaxation, power law increase of the
relaxation time and high fragility index. At an effective spinodal temperature
Tsp the relaxation time exceeds the crystal nucleation time, and the
supercooled liquid loses stability. Below Tsp liquid properties cannot be
extrapolated, in line with Kauzmann's scenario of a `lower metastability limit'
of supercooled liquids as a solution of Kauzmann's paradox. The off-equilibrium
dynamics below Tsp corresponds to fast nucleation of small, but stable, crystal
droplets, followed by extremely slow growth, due to the presence of pinning
energy barriers. In the early time region, which is longer the lower the
temperature, this crystal-growth phase is indistinguishable from an
off-equilibrium glass, both from a structural and a dynamical point of view:
crystal growth has not advanced enough to be structurally detectable, and a
violation of the fluctuation-dissipation theorem (FDT) typical of structural
glasses is observed. On the other hand, for longer times crystallization
reaches a threshold beyond which crystal domains are easily identified, and FDT
violation becomes compatible with ordinary domain growth.Comment: 25 page
Supersymmetric quenched complexity in the Sherrington-Kirkpatrick model
By using the BRST supersymmetry we compute the quenched complexity of the TAP
states in the SK model. We prove that the BRST complexity is equal to the
Legendre transform of the static free energy with respect to the largest
replica symmetry breaking point of its overlap matrix
Specific heat anomaly in a supercooled liquid with amorphous boundary conditions
We study the specific heat of a model supercooled liquid confined in a
spherical cavity with amorphous boundary conditions. We find the equilibrium
specific heat has a cavity-size-dependent peak as a function of temperature.
The cavity allows us to perform a finite-size scaling (FSS) analysis, which
indicates that the peak persists at a finite temperature in the thermodynamic
limit. We attempt to collapse the data onto a FSS curve according to different
theoretical scenarios, obtaining reasonable results in two cases: a
"not-so-simple" liquid with nonstandard values of the exponents {\alpha} and
{\nu}, and random first-order theory, with two different length scales.Comment: Includes Supplemental Materia
Interface Fluctuations, Burgers Equations, and Coarsening under Shear
We consider the interplay of thermal fluctuations and shear on the surface of
the domains in various systems coarsening under an imposed shear flow. These
include systems with nonconserved and conserved dynamics, and a conserved order
parameter advected by a fluid whose velocity field satisfies the Navier-Stokes
equation. In each case the equation of motion for the interface height reduces
to an anisotropic Burgers equation. The scaling exponents that describe the
growth and coarsening of the interface are calculated exactly in any dimension
in the case of conserved and nonconserved dynamics. For a fluid-advected
conserved order parameter we determine the exponents, but we are unable to
build a consistent perturbative expansion to support their validity.Comment: 10 RevTeX pages, 2 eps figure
Response to "Comment on Static correlations functions and domain walls in glass-forming liquids: The case of a sandwich geometry" [J. Chem. Phys. 144, 227101 (2016)]
The point-to-set correlation function has proved to be a very valuable tool
to probe structural correlations in disordered systems, but more than that, its
detailed behavior has been used to try to draw information on the mechanisms
leading to glassy behavior in supercooled liquids. For this reason it is of
primary importance to discern which of those details are peculiar to glassy
systems, and which are general features of confinement. Within the present
response we provide an answer to the concerns raised in [J. Chem. Phys. 144,
227101 (2016)]
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