5 research outputs found
How a spin-glass remembers. Memory and rejuvenation from intermittency data: an analysis of temperature shifts
The memory and rejuvenation aspects of intermittent heat transport are
explored theoretically and by numerical simulation for Ising spin glasses with
short-ranged interactions. The theoretical part develops a picture of
non-equilibrium glassy dynamics recently introduced by the authors. Invoking
the concept of marginal stability, this theory links irreversible
`intermittent' events, or `quakes' to thermal fluctuations of record magnitude.
The pivotal idea is that the largest energy barrier surmounted prior
to by thermal fluctuations at temperature determines the rate of the intermittent events occurring near . The idea leads
to a rate of intermittent events after a negative temperature shift given by
, where the `effective age' has
an algebraic dependence on , whose exponent contains the temperatures
before and after the shift. The analytical expression is verified by numerical
simulations. Marginal stability suggests that a positive temperature shift could erase the memory of the barrier . The simulations show
that the barrier controls the intermittent dynamics,
whose rate is hence .
Additional `rejuvenation' effects are also identified in the intermittency
data for shifts of both signs.Comment: Revised introduction and discussion. Final version to appear in
Journal of Statistical Mechanics: Theory and Experimen
Exploring valleys of aging systems: the spin glass case
We present a statistical method for complex energy landscape exploration
which provides information on the metastable states—or
valleys—actually explored by an unperturbed
aging process following a quench. Energy fluctuations of
record size are identified as the events which move the system
from one valley to the next. This allows for a semi-analytical
description in terms of log-Poisson statistics, whose main features are
briefly explained. The bulk of the paper is devoted to thorough
investigations of Ising spin glasses with Gaussian interactions of
both short and long range,
a well established paradigm for glassy dynamics.
Simple scaling expressions with universal exponents for
(a) barrier energies, (b) energy minima, and (c)
the Hamming distance as a function of the valley index are
found. The distribution of residence time inside valleys entered at
age tw is investigated, along with the distribution of
time at which the global minimum inside a valley is hit.
Finally, the correlations between the minima of the landscape are
presented.
The results fit well into the framework of available
knowledge about spin glass aging. At the same time
they support a novel interpretation of thermal relaxation
in complex landscapes with multiple metastable states.
The marginal stability of the attractors selected is
emphasized and explained in terms of geometrical properties
of the landscape