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1.
F. Krzakala O.C. Martin 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(2):199-208
We address the problem of chaotic temperature dependence in disordered glassy systems at equilibrium by following states of
a random-energy random-entropy model in temperature; of particular interest are the crossings of the free-energies of these
states. We find that this model exhibits strong, weak or no temperature chaos depending on the value of an exponent. This
allows us to write a general criterion for temperature chaos in disordered systems, predicting the presence of temperature
chaos in the Sherrington-Kirkpatrick and Edwards-Anderson spin glass models, albeit when the number of spins is large enough.
The absence of chaos for smaller systems may justify why it is difficult to observe chaos with current simulations. We also
illustrate our findings by studying temperature chaos in the naıve mean field equations for the Edwards-Anderson spin glass.
Received 27 March 2002 Published online 19 July 2002 相似文献
2.
B. Drossel H. Bokil M.A. Moore A.J. Bray 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(2):369-375
We study the link overlap between two replicas of an Ising spin glass in three dimensions using the Migdal-Kadanoff approximation
and scaling arguments based on the droplet picture. For moderate system sizes, the distribution of the link overlap shows
the asymmetric shape and large sample-to-sample variations found in Monte-Carlo simulations and usually attributed to replica
symmetry breaking. However, the scaling of the width of the distribution, and the link overlap in the presence of a weak coupling
between the two replicas are in agreement with the droplet picture. We also discuss why it is impossible to see the asymptotic
droplet-like behaviour for moderate system sizes and temperatures not too far below the critical temperature.
Received 25 May 1999 相似文献
3.
S. Miyashita E. Vincent 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(2):203-211
Aging in spin glasses (and in some other systems) reveals astonishing effects of `rejuvenation and memory' upon temperature
changes. In this paper, we propose microscopic mechanisms (at the scale of spin-spin interactions) which can be at the origin
of such phenomena. Firstly, we recall that, in a frustrated system, the effective average interaction between two spins may take different values (possibly with opposite signs) at different temperatures. We give simple examples
of such situations, which we compute exactly. Such mechanisms can explain why new ordering processes (rejuvenation) seem to take place in spin glasses when the temperature is lowered. Secondly, we emphasize the fact that inhomogeneous interactions do naturally lead to a wide distribution of relaxation times for thermally activated flips. `Memory spots' spontaneously
appear, in the sense that the flipping time of some spin clusters becomes extremely long when the temperature is decreased.
Such memory spots are capable of keeping the memory of previous ordering at a higher temperature while new ordering processes occur at a lower temperature. After a qualitative
discussion of these mechanisms, we show in the numerical simulation of a simplified example that this may indeed work. Our
conclusion is that certain chaos-like phenomena may show up spontaneously in any frustrated and inhomogeneous magnetic system, without impeding the occurrence of memory effects.
Received 5 February 2001 and Received in final form 27 April 2001 相似文献
4.
A. Montanari F. Ricci-Tersenghi 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(3):339-346
The low-temperature phase of discontinuous mean-field spin glasses is generally described by a one-step replica symmetry breaking
(1RSB) ansatz. The Gardner transition, i.e. a very-low-temperature phase transition to a full replica symmetry breaking (FRSB) phase, is often regarded as an inessential, and
somehow exotic phenomenon. In this paper we show that the metastable states which are relevant for the out-of-equilibrium
dynamics of such systems are always in a FRSB phase. The only exceptions are (to the best of our knowledge) the p-spin spherical model and the random energy model (REM). We also discuss the consequences of our results for aging dynamics
and for local search algorithms in hard combinatorial problems.
Received 10 February 2003 Published online 20 June 2003
RID="a"
ID="a"e-mail: Federico.Ricci@roma1.infn.it
RID="b"
ID="b"UMR 8549, Unité Mixte de Recherche du Centre National de la Recherche Scientifique et de l' école Normale Supérieure 相似文献
5.
R.L. Leheny Y.S. Lee G. Shirane R.J. Birgeneau 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(3):287-290
Inelastic neutron scattering with high wave-vector resolution has characterized the propagation of transverse spin wave modes
near the antiferromagnetic zone center in the metastable domain state of a random field Ising magnet. A well-defined, long
wavelength excitation is observed despite the absence of long-range magnetic order. Direct comparisons with the spin wave
dispersion in the long-range ordered antiferromagnetic state reveal no measurable effects from the domain structure. This
result recalls analogous behavior in thermally disordered anisotropic spin chains but contrasts sharply with that of the phonon
modes in relaxor ferroelectrics.
Received 2 November 2002 / Received in final form 4 February 2003 Published online 11 April 2003
RID="a"
ID="a"leheny@pha.jhu.edu 相似文献
6.
L. Bellon S. Ciliberto C. Laroche 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(2):223-231
A new kind of memory effect on low frequency dielectric measurements on plexiglass (PMMA) is described. These measurements
show that cooling and heating the sample at constant rate give an hysteretic dependence on temperature of the dielectric constant
ε. A temporary stop of cooling produces a downward relaxation of ε. Two main features are observed (i) when cooling is resumed
ε goes back to the values obtained without the cooling stop (i.e. the low temperature state is independent of the cooling history) (ii) upon reheating ε keeps the memory of all the cooling
stops (Advanced memory). The dependence of this effect on frequency and on the cooling rate is analyzed. The memory deletion is studied too. Finally
the results are compared with those of similar experiments done in spin glasses and with the famous experiments of Kovacs.
Received 24 September 2001 and Received in final form 20 November 2001 相似文献
7.
A simple model for systems of dipolarly interacting single-domain ultrafine ferromagnetic particles is studied by Monte Carlo
simulations of zero field cooling and field cooling as well as relaxation experiments. By investigating systems characterized
by an identical moderate concentration but different types of particle positions' disorder, it is shown that the positional
disorder has a crucial influence on the magnetic behavior of the system. For extreme values of positional disorder, the interplay
between spatial disorder and dipolar interaction can even lead to a cooperative freezing at low temperatures.
Received 28 November 2001 相似文献
8.
A.F.S. Moreira W. Figueiredo V.B. Henriques 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(1):153-159
We performed a detailed Landau expansion of the free energy for a metamagnetic model considering terms up to twelfth order.
We obtained explicit expressions for the coefficients as a function of the temperature and the ratio between ferro- and antiferromagnetic
interactions. We showed that a naive analysis based on the signs of these coefficients cannot always give us sufficient guarantee
about the correctness of the phase diagram of the model. In these cases it is necessary to resort to the full expression of
the free energy in order to characterize the nature of the phase transition.
Received 28 November 2001 相似文献
9.
E. Brézin C. De Dominicis 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(1):71-76
The field theory of a short range spin glass with Gaussian random interactions, is considered near the upper critical dimension
six. In the glassy phase, replica symmetry breaking is accompanied with massless Goldstone modes, generated by the breaking
of reparametrization invariance of a Parisi type solution. Twisted boundary conditions are thus imposed at two opposite ends
of the system in order to study the size dependence of the twist free energy. A loop-expansion is performed to first order
around a twisted background. It is found, as expected but it is non trivial, that the theory does renormalize around such
backgrounds, as well as for the bulk. However two main differences appear, in comparison with simple ferromagnetic transitions:
(i) the loop expansion yields a (negative) anomaly in the size dependence of the free energy, thereby lifting the lower critical
dimension to a value greater than two (ii) the free energy is lowered by twisting the boundary conditions. This situation
is common in spin glasses, reflecting the non-positivity of mode multiplicity in replica symmetry breaking, but its physical
meaning is still unclear.
Received 12 April 2002 / Received in final form 30 July 2002 Published online 19 November 2002 相似文献
10.
F. Mila D. Dean 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):301-306
Motivated by the observation of a spin-glass transition in almost disorder-free Kagome antiferromagnets, and by the specific
form of the effective low-energy model of the S = 1/2, trimerized Kagome antiferromagnet, we investigate the possibility to obtain a spin-glass behavior in two-component,
disorder-free models. We concentrate on a toy-model, a modified Ashkin-Teller model in a magnetic field that couples only
to one species of spins, for which we prove that a dynamic spin-glass behavior occurs. The dynamics of the magnetization is
closely related to that of the underlying Ising model in zero field in which spins and pseudo-spins are intimately coupled.
The spin-glass like history dependence of the magnetization is a consequence of the ageing of the underlying Ising model.
Received 21 September 2001 and Received in final form 16 January 2002 相似文献
11.
12.
K.S.D. Beach R.J. Gooding 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(4):579-591
We examine the role of spin twists in the formation of domain walls, often called stripes, by focusing on the spin textures
found in the cluster spin glass phases of and . To this end, we derive improved analytic expressions for the spin distortions produced by a frustrating bond, both near
the core region of the bond and in the far field, and then derive an improved expression for interaction energies between
such bonds. We critique our analytical theory by comparison to numerical solutions of this problem and find excellent agreement.
By looking at collections of small numbers of such bonds localized in some region of a lattice, we demonstrate the stability
of small “clusters” of spins, each cluster having its own orientation of its antiferromagnetic order parameter. Then, we display
a domain wall corresponding to spin twists between clusters of locally ordered spins showing how spin twists can serve as
a mechanism for stripe formation. Since the charges are localized in this model, we emphasize that these domain walls are
produced in a situation for which no kinetic energy is present in the problem.
Received 10 January 2000 相似文献
13.
S. Moreno R.G. Rubio G. Luengo F. Ortega M.G. Prolongo 《The European physical journal. E, Soft matter》2001,4(2):173-182
The complex dielectric permittivity has been measured for three poly(ethylenglycol)-b-poly(propylenglycol)-b-poly(ethylenglycol)
copolymers with different content of poly(ethylenglycol) (15%, 33% and 80%), and increasing degree of crystallinity (0%, 10%
and 20%, respectively). Only the non-crystalline sample shows the normal mode relaxation together with the segmental (α-relaxation)
and the Johari-Goldstein (β-relaxation) modes. The crystalline samples show also polarization contributions due to the existence
of interfaces between the crystallites and the amorphous phase. The relaxation times of the (α and normal modes can be described
by a VFT equation with the same value of T0. There is a slowing-down of the segmental mode due to the presence of crystallites. The temperature dependence of the α and
β relaxations in the copolymers is very similar to that found in pure PPG, while there are significant differences in the
case of the normal mode of the non-crystalline sample. The size of the cooperatively rearranging regions CRR, and the width
of the glass transition region increase slightly with the degree of crystallinity. The temperature dependence of the size
of CRRs is compatible with the prediction of fluctuation theory. No systematic effect of the degree of crystallinity on the
β-relaxation has been found. Near T
g the β-relaxation time is close to the primitive time of the coupling model.
Received: 31 May 2000 相似文献
14.
C. Djurberg K. Jonason P. Nordblad 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(1):15-21
Experiments on the temperature and time dependence of the response function and the field cooled magnetisation of a Cu(Mn)
spin glass at temperatures below the zero field spin glass temperature are used to explore the non-equilibrium nature of the
underlying spin configuration. The results imply that a certain spin configuration is imprinted on the system as the temperature
is decreased at a constant cooling rate. The cooling rate governs the magnitude of the FC magnetisation ((H,T)). Any intermittent halt at a constant temperature, , imprints an extended spin configuration, a process that is reflected e.g. in a downward relaxation of . On continued cooling at the same rate, the magnitude of (T) remains at a lower level than that of a continuous cooling curve. These results are put into the context of the corresponding
behaviour of the response function as observed in measurements of the relaxation of the zero field cooled magnetisation.
Received 27 October 1998 and Received in final form 30 November 1998 相似文献
15.
Dilational rheology of monolayers of a miscible polymer blend: From good- to poor-solvent conditions
Rivillon S Monroy F Ortega F Rubio RG 《The European physical journal. E, Soft matter》2002,9(4):375-385
The viscoelastic moduli (elasticity and dilational viscosity) of monolayers of PVAc + P4HS has been studied over a broad frequency
range (0.1 mHz-200 kHz) using a combination of relaxation and capillary-waves techniques. The analysis of the surface pressure,
the elasticity and the viscosity on the semidilute regime show that the air-water interface is a good solvent for the monolayers
of PVAc-rich blends, and a poor (near-Θ) solvent for the monolayers of P4HS-rich blends. The solvent quality changes continuously
over a broad concentration range. The results of viscoelastic moduli show that there is a broad relaxation process in the
low-frequency range ( ω < 1 Hz). While for PVAc-rich monolayers this relaxation process follows the reptation-like behavior
described by Noskov, for P4HS-rich monolayers the model does not describe the amplitudes of the different relaxation modes.
For PVAc-rich monolayers two processes are clearly distinguished at higher frequencies: one centered at around 500 Hz and
another one at around 40 kHz. However, for P4HS-rich monolayers only one broad relaxation mode is found below 1 kHz. The crossover
from one type of behavior to the other one takes place in a very narrow blend-composition range, and is not clearly related
to the crossover from good- to poor-solvent condition.
Received 7 June 2002 and Received in final form 5 November 2002
RID="a"
ID="a"Current address: Complex Fluids Lab., Cranbury Res. Ctr., Rhodia Inc., Cranbury, NJ 08512-7500, USA.
RID="b"
ID="b"e-mail: rgrubio@quim.ucm.es 相似文献
16.
R. Florian S. Galam 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(1):189-194
Coalition setting among a set of actors (countries, firms, individuals) is studied using concepts from the theory of spin
glasses. Given the distribution of respective bilateral propensities to either cooperation or conflict, the phenomenon of
local aggregation is modeled. In particular the number of coalitions is determined according to a minimum conflict principle.
It is found not to be always two. Along these lines, previous studies are revisited and are found not to be consistent with
their own principles. The model is then used to describe the fragmentation of former Yugoslavia. Results are compared to the
actual situation.
Received 23 February 2000 相似文献
17.
E.T. Seppälä M.J. Alava 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(3):407-424
We study the effect of an external field on (1 + 1) and (2 + 1) dimensional elastic manifolds, at zero temperature and with
random bond disorder. Due to the glassy energy landscape the configuration of a manifold changes often in abrupt, “first order”-type
of large jumps when the field is applied. First the scaling behavior of the energy gap between the global energy minimum and
the next lowest minimum of the manifold is considered, by employing exact ground state calculations and an extreme statistics
argument. The scaling has a logarithmic prefactor originating from the number of the minima in the landscape, and reads ΔE
1∼L
θ[ln(L
z
L
- ζ)]-1/2, where ζ is the roughness exponent and θ is the energy fluctuation exponent of the manifold, L is the linear size of the manifold, and Lz is the system height. The gap scaling is extended to the case of a finite external field and yields for the susceptibility
of the manifolds ∼L
2D + 1 - θ[(1 - ζ)ln(L)]1/2. We also present a mean field argument for the finite size scaling of the first jump field, h
1∼L
d - θ. The implications to wetting in random systems, to finite-temperature behavior and the relation to Kardar-Parisi-Zhang non-equilibrium
surface growth are discussed.
Received December 2000 and Received in final form April 2001 相似文献
18.
Ellison CJ Kim SD Hall DB Torkelson JM 《The European physical journal. E, Soft matter》2002,8(2):155-166
Fluorescence intensity measurements of chromophore-doped or -labeled polymers have been used for the first time to determine
the effects of decreasing film thickness on glass transition temperature, T
g, the relative strength of the glass transition, and the relative rate of physical aging below T
g in supported, ultrathin polymer films. The temperature dependence of fluorescence intensity measured in the glassy state
of thin and ultrathin films of pyrene-doped polystyrene (PS), poly(isobutyl methacrylate) (PiBMA), and poly(2-vinylpyridine)
(P2VP) differs from that in the rubbery state with a transition at T
g. Positive deviations from bulk T
g are observed in ultrathin PiBMA and P2VP films on silica substrates while substantial negative deviations from bulk T
g are observed in ultrathin PS films on silica substrates. The relative difference in the temperature dependences of fluorescence
intensity in the rubbery and glassy states is usually reduced with decreasing film thickness, indicating that the strength
of the glass transition is reduced in thinner films. The temperature dependence of fluorescence intensity also provides useful
information on effects of processing history as well as on the degree of polymer-substrate interaction. In addition, when
used as a polymer label, a mobility-sensitive rotor chromophore is demonstrated to be useful in measuring relative rates of
physical aging in films as thin as 10 nm.
Received 21 August 2001 相似文献
19.
P.K. Mukherjee H. Pleiner H.R. Brand 《The European physical journal. E, Soft matter》2001,4(3):293-297
A simple Landau-type free energy function is presented to describe the smectic-A-isotropic phase transition. Varying the coupling
between orientational and positional order parameters, a smectic-A-isotropic or a nematic-isotropic phase transition occurs.
Within this model the smectic-A-isotropic phase transition is found to be always more strongly first order than the nematic-isotropic
phase transition. The theoretical results are found to be in good agreement with all published experimental results.
Received 27 June 2000 相似文献
20.
F. Baffioni F. Rosati 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(3):439-447
The mean field spin glass model is analyzed by a combination of exact methods and a simple Ansatz. The method exploited is general, and can be applied to others disordered mean field models such as, e.g., neural networks. It is well known that the probability measure of overlaps among replicas carries the whole physical content
of these models. A functional order parameter of Parisi type is introduced by rigorous methods, according to previous works
by F. Guerra. By the Ansatz that the functional order parameter is the correct order parameter of the model, we explicitly find the full overlap distribution.
The physical interpretation of the functional order parameter is obtained, and ultrametricity of overlaps is derived as a
natural consequence of a branching diffusion process. It is shown by explicit construction that ultrametricity of the 3-replicas
overlap distribution together with the Ghirlanda-Guerra relations determines the distribution of overlaps among s replicas, for any s, in terms of the one-overlap distribution.
Received 14 February 2000 相似文献