共查询到20条相似文献,搜索用时 15 毫秒
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.
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
3.
M. Sasaki V. Dupuis J.-P. Bouchaud E. Vincent 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(3):469-479
We study the deviations from perfect memory in negative temperature cycle spin glass experiments. It is known that the a.c.
susceptibility after the temperature is raised back to its initial value is superimposed to the reference isothermal curve
for large enough temperature jumps ΔT (perfect memory). For smaller ΔT, the deviation from this perfect memory has a striking non monotonous behavior: the `memory anomaly' is negative for small ΔT's, becomes positive for intermediate ΔT's, before vanishing for still larger ΔT's. We show that this interesting behavior can be reproduced by simple Random Energy trap models. We discuss an alternative
interpretation in terms of droplets and temperature chaos.
Received 23 May 2002 Published online 14 October 2002
RID="a"
ID="a"e-mail: sasaki@ipno.in2p3.fr 相似文献
4.
A.V. Pan P. Esquinazi 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(3):405-410
We have investigated the influence of a driving force on the elastic coupling (Labusch parameter) of the field-cooled state
of the flux line lattice (FLL) in 400 nm thick YBa2Cu3O7 superconducting films. We found that the FLL of a field-cooled state without driving forces is not in an equilibrium state.
Results obtained for magnetic fields applied at and 30 relative to CuO2 planes, show an enhancement of the elastic coupling of the films at driving current densities several orders of magnitude
smaller than the critical one. Our results indicate that the FLL appears to be in a relatively ordered, metastable state after
field cooling without driving forces.
Received 21 December 1999 相似文献
5.
L. Fruchter 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(3):313-317
The dynamic transition between ordered flow and plastic flow is studied for a two-dimensional driven vortex lattice, in the
presence of sharp and dense pinning centers, from numerical simulations. For this system, which does not show smectic ordering,
the lattice exhibits a first order transition from a crystal to a liquid, shortly followed by the dynamical transition to
plastic flow. The resistivity provides a critical order parameter for the latter, and critical exponents are determined in
analogy with a percolation transition. At the boundary between a pinned region and an unpinned one, an anomalous layer is
observed, where the vortices are more strongly pinned than in the bulk.
Received 22 September 2001 相似文献
6.
7.
For one-component volatile fluids governed by dispersion forces an effective interface Hamiltonian, derived from a microscopic
density functional theory, is used to study complete wetting of geometrically structured substrates. Also the long range of
substrate potentials is explicitly taken into account. Four types of geometrical patterns are considered: i) one-dimensional
periodic arrays of rectangular or parabolic grooves and ii) two-dimensional lattices of cylindrical or parabolic pits. We
present numerical evidence that at the centers of the cavity regions the thicknesses of the adsorbed films obey precisely
the same geometrical covariance relation, which has been recently reported for complete cone and wedge filling. However, this
covariance does not hold for the laterally averaged wetting film thicknesses. For sufficiently deep cavities with vertical
walls and close to liquid-gas phase coexistence in the bulk, the film thicknesses exhibit an effective planar scaling regime,
which as a function of undersaturation is characterized by a power law with the common critical exponent -1/3 as for a flat
substrate, but with the amplitude depending on the geometrical features. 相似文献
8.
T. Di Luccio C. Attanasio A. Andreone A.M. Cucolo 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(3):263-268
We investigated the vortex lattice ordering induced by an applied current in thick (700-900 nm) Mo-Re films with strong pinning.
Measurements of I-V characteristics as a function of field and at different temperatures were carried out. We found that, as in the case of weakly
pinning amorphous samples, dynamic ordering can occur only if the size of the vortex correlated region is at least two times
the intervortex distance.
Received 20 July 2001 相似文献
9.
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
10.
N.A. Taylanov G.R. Berdiyorov 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(3):343-348
The problem of the thermal and magnetic destruction of the critical state in composite superconductors is investigated. The
initial distributions of temperature and electromagnetic field are assumed to be essentially inhomogeneous. The limit of the
thermomagnetic instability in quasi-stationary approximation is determined. The obtained integral criterion, unlike the analogous
criterion for a homogeneous temperature profile, is shown to take into account the influence of any part of the superconductor
on the threshold for critical-state instability.
Received 11 October 2001 / Received in final form 30 November 2002 Published online 14 February 2003
RID="a"
ID="a"e-mail: taylanov@iaph.tkt.uz 相似文献
11.
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
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.
T. Emig T. Nattermann 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(4):525-546
The simultaneous effect of both disorder and crystal-lattice pinning on the equilibrium behavior of oriented elastic objects
is studied using scaling arguments and a functional renormalization group technique. Our analysis applies to elastic manifolds,
e.g., interfaces, as well as to periodic elastic media, e.g., charge-density waves or flux-line lattices. The competition between both pinning mechanisms leads to a continuous, disorder
driven roughening transition between a flat state where the mean relative displacement saturates on large scales and a rough
state with diverging relative displacement. The transition can be approached by changing the impurity concentration or, indirectly,
by tuning the temperature since the pinning strengths of the random and crystal potential have in general a different temperature
dependence. For D dimensional elastic manifolds interacting with either random-field or random-bond disorder a transition exists for 2<D<4, and the critical exponents are obtained to lowest order in . At the transition, the manifolds show a superuniversal logarithmic roughness. Dipolar interactions render lattice effects
relevant also in the physical case of D=2. For periodic elastic media, a roughening transition exists only if the ratio p of the periodicities of the medium and the crystal lattice exceeds the critical value . For p<p
c
the medium is always flat. Critical exponents are calculated in a double expansion in and and fulfill the scaling relations of random field models.
Received 28 August 1998 相似文献
14.
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
15.
E. Mezzetti A. Chiodoni R. Gerbaldo G. Ghigo L. Gozzelino B. Minetti C. Camerlingo C. Giannini 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(3):357-362
This paper reports on the striking correlation between nanosize mosaic domain walls in YBCO films and 1D rows of parallel
Josephson junctions, determining the J
c
vs.B curves. From X-ray data analysis, it results that the average “hidden" domain wall, faceted at a nanometric scale, is almost
mimicking the Josephson Junction (JJ) 1D array. The assumption that the JJs and the domain-wall arrays are coincident, enables
to find out the particular scaling field, making the J
c
vs.B curves independent of temperature. This scaling field can be interpreted in terms of the Josephson nature of the transport
current across these particular patterns in the intermediate temperature range. By means of our model it is also possible
to calculate two asymptotic behaviors of the pinning force as a function of field, for low and high fields, respectively.
These behaviors are punctually repeated by the experimental results in the same asymptotic limit, so that two corresponding
vortex regimes are clearly pointed out. All results can be interpreted by concluding that in the intermediate temperature
range, the strong pinning observed in high quality YBCO films is due to the Josephson Junctions average patterns. These patterns
are the counterpart related to the transport mechanisms of “hidden" structural nano-domains.
Received 16 October 2000 and Received in final form 28 November 2000 相似文献
16.
R. Paul M. Alava H. Rieger 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(3):357-367
The random field q-states Potts model is investigated using exact groundstates and finite-temperature transfer matrix calculations. It is found
that the domain structure and the Zeeman energy of the domains resembles for general q the random field Ising case (q = 2). This is also the expected outcome based on a random-walk picture of the groundstate. The domain size distribution is
exponential, and the scaling of the average domain size with the disorder strength is similar for q arbitrary. The zero-temperature properties are compared to the equilibrium spin states at small temperatures, to investigate
the effect of local random field fluctuations that imply locally degenerate regions. The response to field perturbations (`chaos')
and the susceptibility are investigated. In particular for the chaos exponent it is found to be 1 for q = 2,..., 5. Finally for q = 2 (Ising case) the domain length distribution is studied for correlated random fields.
Received 27 August 2002 Published online 19 December 2002
RID="a"
ID="a"e-mail: rieger@lusi-sb.de 相似文献
17.
18.
A. Pautrat A. Daignere C. Goupil Ch. Simon B. Andrzejewski A.I. Rykov S. Tajima 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(3):279-284
We report complex impedance measurements in an untwinned YBaCuO crystal. Our broad frequency range covers both the quasi static
response and the resistive response of the vortex lattice. It allow us to characterize the irreversibility line without the
need of any frequency dependent pinning parameters. We confirm the validity of the two modes model of vortex dynamic, and
extract both the surface critical current and the flux flow resistivity around the first order transition Tm. This latter is identified by the abrupt loss of pinning and by an unexpected step of (T) at Tm.
Received 22 November 2002 / Received in final form 17 February 2003 Published online 20 June 2003
RID="a"
ID="a"e-mail: alain.pautrat@ismra.fr
RID="b"
ID="b"UMR 6508 associée au CNRS 相似文献
19.
20.
H.A. Radovan H.H. Wen P. Ziemann 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(4):533-540
Using a specially designed SQUID magnetometer we measured the temperature dependence of the critical current density in a
ring patterned thin film for magnetic fields parallel to the c-axis. In addition, the temporal relaxation of the remanent state as prepared by field cooling in an external field of 100
Oe at different temperatures is determined. The j
c
(
T
) data show a field-dependent anomalous kink close to Tc pointing to reduced dissipation with increasing temperature allowing to construct a corresponding H-T borderline. A similar behavior is observed for the normalized relaxation rate S
(
T
) as extracted from the temporal behavior of the remanent state, which, at low temperatures, exhibits the expected increase
for increasing T-values, while an anomalous decrease of S
(
T
) is found for temperatures above 85 K. While the low-T regime is attributed to creep of 2D pinned single vortex lines, the high-T behavior is suggested to be dominated by collective motion with a more sluggish dynamics. This change in dynamics is also
reflected by the activation barriers for flux creep U
(
j
), which show a corresponding crossover in μ from 0.06 to 0.99. An additional scaling analysis of the E-j characteristics for according to vortex glass theory reveals quasi-2D collective creep behavior with .
Received: 8 April 1998 / Revised: 15 July 1998 / Accepted: 2 September 1998 相似文献