Search results for "Statistical physics"

Critical behaviour of coupled spin chains

1991

The authors investigate, using numerical computation of the eigenvalues of short chains, the critical behaviour of two composite spin models, which interpolate smoothly between isotropic Heisenberg chains with different values of S. For the first model which interpolates between S=1/2 and S=3/2 they find that the model is critical over the whole range and the values of the central charge and critical exponents (scaling dimensions) appear to be constant in the thermodynamic limit. In the second model, which interpolates between S=1/2 and S=1 they find that, except at S=1/2, the central charge is effectively zero, implying a non-critical behaviour.

Anomalous magneto-transport in disordered structures: classical edge-state percolation

2015

By event-driven molecular dynamics simulations we investigate magneto-transport in a two-dimensional model with randomly distributed scatterers close to the field-induced localization transition. This transition is generated by percolating skipping orbits along the edges of obstacle clusters. The dynamic exponents differ significantly from those of the conventional transport problem on percolating systems, thus establishing a new dynamic universality class. This difference is tentatively attributed to a weak-link scenario, which emerges naturally due to barely overlapping edge trajectories. We make predictions for the frequency-dependent conductivity and discuss implications for active coll…

Dynamic Self-assembly of Non-Brownian Spheres.

2017

International audience; Granular self-assembly of confined non-Brownian spheres under gravity is studied by Molecular Dynamics simulations. Starting from a disordered phase, dry or cohesive spheres organize, by vibrational an-nealing into BCT or FCC structures, respectively. During the self-assembling process, isothermal and isodense points are observed. The existence of such points indicates that both granular temperature and packing fraction undergo an inversion process. Around the isothermal point, a sudden growth of beads having the maximum coordination number takes place. We show by a density fluctuation analysis that a transition form a disordered phase to a crystalline structure may …

Finite-size scaling analysis of the anisotropic critical behavior of the two-dimensional Ising model under shear

2010

The critical behavior of the two-dimensional Ising Model with non-conserved order parameter in steady-state shear is studied by large-scale Monte Carlo simulations. Studying the structure factor S(qx,qy) in the disordered phase, the ratio of correlation length exponents νx/νy in the two lattice directions (x,y) is estimated, and the critical temperature is determined as a function of the shear rate as Tc() − Tc(0) ∝ with ≈0.45. Critical exponents β≈0.37, γ≈1.1, ; ν⊥≈0.46, ν∥≈1.38 are roughly compatible with anisotropic hyperscaling.

High-temperature series expansion for the relaxation times of the two dimensional Ising model

1995

We derive the high temperature series expansions for the two relaxation times of the single spin-flip kinetic Ising model on the square lattice. The series for the linear relaxation time τl is obtained with 20 non-trivial terms, and the analysis yields 2.183±0.005 as the value of the critical exponentΔl, which is equal to the dynamical critical exponentz in the two-dimensional case. For the non-linear relaxation time we obtain 15 non-trivial terms, and the analysis leads to the resultsΔnl = 2.08 ± 0.07. The scaling relationΔl −Δnl = β (β being the exponent of the order parameter) seems to be fulfilled, though the error bars ofΔnl are still quite substantial. In addition, we obtain the serie…

Interface localization transition in Ising films with competing walls: Ginzburg criterion and crossover scaling.

1996

The Ising model as a playground for the study of wetting and interface behavior

2000

Computer simulations have played an important role in the elucidation of wetting and interface unbinding phenomena. In particular, use of the Ising-lattice-gas model in a film geometry and subject to diverse surface and bulk magnetic fields has permitted extensive Monte Carlo simulations to reveal new features of the phase diagrams associated with these phenomena and to provoke new theoretical studies. The status of our knowledge about the nature of wetting and interface-delocalization transitions which has resulted from these Ising model simulations will be summarized.

The high-temperature dynamics of a mean-field Potts glass

2002

Abstract We use Monte Carlo simulations to investigate the dynamic properties of the ten-state infinite-range Potts glass. By analyzing the spin autocorrelation function for system sizes up to N = 2560, we show that strong finite size effects are present around the predicted dynamic transition temperature. The autocorrelation function shows strong self-averaging at high temperatures, whereas close to the dynamic transition shows lack of self-averaging.

Simple monoclinic crystal phase in suspensions of hard ellipsoids

2006

We present a computer simulation study on the crystalline phases of hard ellipsoids of revolution. For aspect ratios $\ensuremath{\geqslant}3$ the previously suggested stretched-fcc phase [Frenkel and Mulder, Mol. Phys. 55, 1171 (1985)] is replaced by a different crystalline phase. Its unit cell contains two ellipsoids with unequal orientations. The lattice is simple monoclinic. The angle of inclination of the lattice, $\ensuremath{\beta}$, is a very soft degree of freedom, while the two right angles are stiff. For one particular value of $\ensuremath{\beta}$, the close-packed version of this crystal is a specimen of the family of superdense packings recently reported [Donev et al., Phys. R…

Unified model of fractal conductance fluctuations for diffusive and ballistic semiconductor devices

2006

We present an experimental comparison of magnetoconductance fluctuations measured in the ballistic, quasiballistic, and diffusive scattering regimes of semiconductor devices. In contradiction to expectations, we show that the spectral content of the magnetoconductance fluctuations exhibits an identical fractal behavior for these scattering regimes and that this behavior is remarkably insensitive to device boundary properties. We propose a unified model of fractal conductance fluctuations in the ballistic, quasiballistic, and diffusive transport regimes, in which the generic fractal behavior is generated by a subtle interplay between boundary and material-induced chaotic scattering events.