7,044 research outputs found
Kob-Andersen model: a non-standard mechanism for the glassy transition
We present new results reflecting the analogies between the Kob-Andersen
model and other glassy systems. Studying the stability of the blocked
configurations above and below the transition we also give arguments that
supports their relevance for the glassy behaviour of the model.
However we find, surprisingly, that the organization of the phase space of
the system is different from the well known organization of other mean-field
spin glasses and structural glasses.Comment: New reference added and one update
DYNAMICAL SOLUTION OF A MODEL WITHOUT ENERGY BARRIERS
In this note we study the dynamics of a model recently introduced by one of
us, that displays glassy phenomena in absence of energy barriers. Using an
adiabatic hypothesis we derive an equation for the evolution of the energy as a
function of time that describes extremely well the glassy behaviour observed in
Monte Carlo simulations.Comment: 11 pages, LaTeX, 3 uuencoded figure
A Variational Approach to the Spinless Relativistic Coulomb Problem
By application of a straightforward variational procedure we derive a simple,
analytic upper bound on the ground-state energy eigenvalue of a
semirelativistic Hamiltonian for (one or two) spinless particles which
experience some Coulomb-type interaction.Comment: 7 pages, HEPHY-PUB 606/9
Langevin dynamics of the Lebowitz-Percus model
We revisit the hard-spheres lattice gas model in the spherical approximation
proposed by Lebowitz and Percus (J. L. Lebowitz, J. K. Percus, Phys. Rev.{\
144} (1966) 251). Although no disorder is present in the model, we find that
the short-range dynamical restrictions in the model induce glassy behavior. We
examine the off-equilibrium Langevin dynamics of this model and study the
relaxation of the density as well as the correlation, response and overlap
two-time functions. We find that the relaxation proceeds in two steps as well
as absence of anomaly in the response function. By studying the violation of
the fluctuation-dissipation ratio we conclude that the glassy scenario of this
model corresponds to the dynamics of domain growth in phase ordering kinetics.Comment: 21 pages, RevTeX, 14 PS figure
Phase diagram of glassy systems in an external field
We study the mean-field phase diagram of glassy systems in a field pointing
in the direction of a metastable state. We find competition among a
``magnetized'' and a ``disordered'' phase, that are separated by a coexistence
line as in ordinary first order phase transitions. The coexistence line
terminates in a critical point, which in principle can be observed in numerical
simulations of glassy models.Comment: 4 pages, 5 figure
Glassy Transition and Aging in a Model without Disorder
We study the off-equilibrium relaxational dynamics of the Amit-Roginsky
field theory, for which the mode coupling approximation is exact. We
show that complex phenomena such as aging and ergodicity breaking are present
at low temperature, similarly to what is found in long range spin glasses. This
is a generalization of mode coupling theory of the structural glass transition
to off-equilibrium situations.Comment: 9 pages, 1 uuencoded figure, LaTex, preprint NORDITA 94/3
Magnetic field induced charge and spin instabilities in cuprate superconductors
A d-wave superconductor, subject to strong phase fluctuations, is known to
suffer an antiferromagnetic instability closely related to the chiral symmetry
breaking in (2+1)-dimensional quantum electrodynamics (QED3). On the basis of
this idea we formulate a "QED3 in a box" theory of local instabilities of a
d-wave superconductor in the vicinity of a single pinned vortex undergoing
quantum fluctuations around its equilibrium position. As a generic outcome we
find an incommensurate 2D spin density wave forming in the neighborhood of a
vortex with a concomitant "checkerboard" pattern in the local electronic
density of states, in agreement with recent neutron scattering and tunneling
spectroscopy measurements.Comment: 4 pages REVTeX + 2 PostScript figures included in text. Version to
appear in PRL (minor stylistic changes, references updated). For related work
and info visit http://www.physics.ubc.ca/~fran
Duality and the vibrational modes of a Cooper-pair Wigner crystal
When quantum fluctuations in the phase of the superconducting order parameter
destroy the off-diagonal long range order, duality arguments predict the
formation of a Cooper pair crystal. This effect is thought to be responsible
for the static checkerboard patterns observed recently in various underdoped
cuprate superconductors by means of scanning tunneling spectroscopy. Breaking
of the translational symmetry in such a Cooper pair Wigner crystal may, under
certain conditions, lead to the emergence of low lying transverse vibrational
modes which could then contribute to thermodynamic and transport properties at
low temperatures. We investigate these vibrational modes using a continuum
version of the standard vortex-boson duality, calculate the speed of sound in
the Cooper pair Wigner crystal and deduce the associated specific heat and
thermal conductivity. We then suggest that these modes could be responsible for
the mysterious bosonic contribution to the thermal conductivity recently
observed in strongly underdoped ultraclean single crystals of YBCO tuned across
the superconductor-insulator transition.Comment: 14 pages; 3 figures; corrected the sample size value; version 3 to
appear in PR
Survival of the d-wave superconducting state near the edge of antiferromagnetism in the cuprate phase diagram
In the cuprate superconductor , hole doping in the
layers is controlled by both oxygen content and the degree of oxygen-ordering.
At the composition , the ordering can occur at room
temperature, thereby tuning the hole doping so that the superconducting
critical temperature gradually rises from zero to 20 K. Here we exploit this to
study the c-axis penetration depth as a function of temperature and doping. The
temperature dependence shows the d-wave superconductor surviving to very low
doping, with no sign of another ordered phase interfering with the nodal
quasiparticles. The only apparent doping dependence is a smooth decline of
superfluid density as Tc decreases.Comment: 4 pages, 3 figure
Glassy behavior induced by geometrical frustration in a hard-core lattice gas model
We introduce a hard-core lattice-gas model on generalized Bethe lattices and
investigate analytically and numerically its compaction behavior. If
compactified slowly, the system undergoes a first-order crystallization
transition. If compactified much faster, the system stays in a meta-stable
liquid state and undergoes a glass transition under further compaction. We show
that this behavior is induced by geometrical frustration which appears due to
the existence of short loops in the generalized Bethe lattices. We also compare
our results to numerical simulations of a three-dimensional analog of the
model.Comment: 7 pages, 4 figures, revised versio
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