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Michel Pleimling

Publications and source records attributed to Michel Pleimling.

118 records · Page 7Linked to original sources
arXiv2001

Aging, phase ordering and conformal invariance

In a variety of systems which exhibit aging, the two-time response function scales as $R(t,s)\approx s^{-1-a} f(t/s)$. We argue that dynamical scaling can be extended towards conformal invariance, obtaining thus the explicit form of the scaling function $f$. This quantitative prediction is confirmed in several spin systems, both for $T<T_c$ (phase ordering) and $T=T_c$ (non-equilibrium critical dynamics). The 2D and 3D Ising models with Glauber dynamics are studied numerically, while exact results are available for the spherical model with a non-conserved order parameter, both for short-ranged and long-ranged interactions, as well as for the mean-field spherical spin glass.

hep-th↗
arXiv2001

Phase transitions at surfaces, edges, and corners

Results of large-scale Monte Carlo simulations of three-dimensional Ising models with edges and corners are reviewed. At the ordinary transition, angle dependent critical exponents are observed, whereas at the surface transition edge and corner critical exponents are non-universal and depend on the details of the model. The results obtained at the surface transition are compared to exact findings on critical two-dimensional Ising models with different types of defect lines.

cond-mat↗
arXiv2001

Crossing the coexistence line at constant magnetization

Using Monte Carlo histogram methods, the microcanonical caloric curve is computed for the Ising model in two and three dimensions with fixed magnetization. Whereas the signatures of a first order phase transition are clearly visible for large systems, intriguing finite size effects are revealed for smaller system sizes. The behaviour of the caloric curve is studied in a systematic way. Furthermore, results for the thermal stability of three-dimensional droplets of minority spins inside the two-phase region are presented. The effect of the percolation transition on the stability of these droplets is discussed.

cond-mat↗
arXiv2001

Anisotropic scaling and generalized conformal invariance at Lifshitz points

The behaviour of the 3D axial next-nearest neighbour Ising (ANNNI) model at the uniaxial Lifshitz point is studied using Monte Carlo techniques. A new variant of the Wolff cluster algorithm permits the analysis of systems far larger than in previous studies. The Lifshitz point critical exponents are $α=0.18(2)$, $β=0.238(5)$ and $γ=1.36(3)$. Data for the spin-spin correlation function are shown to be consistent with the explicit scaling function derived from the assumption of local scale invariance, which is a generalization of conformal invariance to the anisotropic scaling {\em at} the Lifshitz point.

hep-th↗
arXiv1998

Comment on "On the $T_S$-Anomaly in Betaine Calcium Chloride Dihydrate"

Recently, Hlinka and Ishibashi [J. Phys. Soc. Jpn. 67, 495 (1998)] discussed the $T_S$-anomaly in betaine calcium chloride dihydrate (BCCD) in a Landau-type approach. We comment on the shortcomings of this approach and discuss the $T_S$-anomaly in the framework of a microscopical pseudo spin model based on a realistic description of BCCD in terms of symmetry-adapted local modes.

cond-mat↗
arXiv1998

Transitions between Phases with Equal Wave Numbers in a Double Ising Spin Model. Application to Betaine Calcium Chloride Dihydrate

A Double Ising Spin model for uniaxially structurally modulated materials exhibits as a special feature phase transitions between phases with equal wave numbers but different pseudo spin configurations. The character of these `internal' transitions is investigated in mean field approximation, with the mean field transfer matrix method, and in Monte Carlo simulations. The structural changes at the transitions are characterized by different strengths of harmonics in a Fourier analysis of the spatial modulation. A dielectric anomaly in the phase diagram of betaine calcium chloride dihydrate (BCCD) and seemingly contradictory structure analyses are explained.

cond-mat↗
arXiv1997

Models for the description of uniaxially modulated materials

Models which allow an explicit application to structurally modulated substances are reviewed within the frame of a symmetry-based approach starting from discrete lattice theory. Focus is set on models formulated in terms of local variables assigned to discrete crystallographic units (unit cells or parts of them). Especially considered are symmetry-based pseudo spin models. Methods are discussed which permit the handling of the statistical mechanics of such models, the translation of model calculation results to a form allowing the prediction of experimental data, and the theoretical determination of point defect influences.

cond-mat↗
arXiv1997

Derivation of symmetry-based pseudo spin models for modulated materials

A general concept for the derivation of symmetry-based pseudo spin Hamiltonians is described. It systematically bridges the gap between the atomistic basis and various pseudo spin models presented in literature. It thus allows the application of the multitude of analytical and numerical procedures derived for the statistical mechanics treatment of the latter to the description of structurally modulated crystals and furnishes a general frame for reviewing these models from a common point of view.

cond-mat↗
arXiv1997

Anomalies in the antiferromagnetic phase of metamagnets

Motivated by recent experiments on the metamagnet FeBr2, anomalies of the magnetization and the specific heat in the antiferromagnetic phase of related spin models are studied systematically using Monte Carlo simulations. In particular, the dependence of the anomalous behavior on competing intralayer interactions, the spin value and the Ising-like anisotropy of the Hamiltonian is investigated. Results are compared to experimental findings on FeBr2.

cond-mat↗