arXiv subjects

W. Selke

Publications and source records attributed to W. Selke.

47 records · Page 3Linked to original sources

arXiv1999

Interfacial adsorption in two-dimensional Potts models

The interfacial adsorption W at the first-order transition in two-dimensional q-state Potts models is studied. In particular, findings of Monte Carlo simulations and of density-matrix renormalization group calculations, at q= 16, are consistent with the analytic result, obtained in the Hamiltonian limit at large values of q, that W \propto t^{-1/3} on approach to the bulk critical temperature T_c, t=|T_c-T|/T_c. In addition, the numerical findings allow to estimate corrections to scaling. Our study supports and specifies a previous conclusion by Bricmont and Lebowitz based on low-temperature expansions.

cond-mat↗

arXiv1999

Stability and diffusion of surface clusters

Using kinetic Monte Carlo simulations and a bond-counting ansatz, thermal stability and diffusion of an adatom island on a crystal surface are studied. At low temperatures, the diffusion constant $D$ is found to decrease for a wide range of island sizes like $D \propto N^{-α}$, where $α$ is close to one, $N$ being the number of adatoms in the cluster. By heating up the surface, the system undergoes a phase transition above which the island disappears. Characteristics of that transition are discussed.

cond-mat↗

arXiv1998

Nonclassical effects and off-diagonal couplings in a model for FeBr2

Using Monte Carlo techniques, we show that the recently experimentally observed transitionlike phenomena in the transverse spin-ordering close to the anomalies in the antiferromagnetic phase of FeBr2 (Petracic et al. [Phys. Rev. B 57, R11051 (1998)]) may result from the quantum nature of the S=1 spins and an off-diagonal exchange between axial and planar spin components.

cond-mat↗

arXiv1998

Edge critical behavior at the surface transition of Ising magnets

Using Monte Carlo techniques, Ising models with ferromagnetic nearest-neighbor interactions on a simple cubic lattice are studied. At the surface transition, the critical exponent $β_2$ of the edge magnetization is found to be non-universal, depending on the edge and edge-surface couplings, in contrast to the situation at the ordinary transition. Results are compared to those for two-dimensional Ising magnets with chain and ladder defects.

cond-mat↗

arXiv1998

Diffusive and subdiffusive step dynamics

The dynamics of steps on crystal surfaces is considered. In general, the meandering of the steps obeys a subdiffusive behaviour. The characteristic asymptotic time laws depend on the microscopic mechanism for detachment and attachment of the atoms at the steps. The three limiting cases of step-edge diffusion, evaporation-condensation and terrace diffusion are studied in the framework of Langevin descriptions and by Monte Carlo simulations.

cond-mat↗

arXiv1998

Specific heat of two-dimensional diluted magnets

Using Monte Carlo techniques, the two-dimensional site-diluted Ising model is studied. In particular, properties of the specific heat, its critical behaviour and the emergence of a non-singular maximum above the transition temperature at moderate concentration of defects, are discussed.

cond-mat↗

arXiv1998

Critical phenomena at edges and corners

Using Monte Carlo techniques, the critical behaviour at edges and corners of the three-dimensional Ising model is studied. In particular, the critical exponent $β_2$ of the local magnetization at edges formed by two intersecting free surfaces is estimated to be, as a function of the opening angle $θ$, $0.96 \pm 0.02$ for $θ= 135^o$, $1.28 \pm 0.04$ for $90^o$, and $2.30 \pm 0.10$ for $45^o$. The critical exponent $β_3$ of the corner magnetization of a cube is found to be $1.86 \pm 0.06$. The Monte Carlo estimates are compared to results of mean field theory, renormalization group calculations and high temperature series expansions.

cond-mat↗

arXiv1997

Boundary critical behaviour of two-dimensional random Ising models

Using Monte Carlo techniques and a star-triangle transformation, Ising models with random, 'strong' and 'weak', nearest-neighbour ferromagnetic couplings on a square lattice with a (1,1) surface are studied near the phase transition. Both surface and bulk critical properties are investigated. In particular, the critical exponents of the surface magnetization, 'beta_1', of the correlation length, 'nu', and of the critical surface correlations, 'eta_{\parallel}', are analysed.

cond-mat.stat-mech↗

arXiv1997

Critical phenomena at perfect and non-perfect surfaces

The effect of imperfections on surface critical properties is studied for Ising models with nearest-neighbour ferromagnetic couplings on simple cubic lattices. In particular, results of Monte Carlo simulations for flat, perfect surfaces are compared to those for flat surfaces with random, 'weak' or 'strong', interactions between neighbouring spins in the surface layer, and for surfaces with steps of monoatomic height. Surface critical exponents at the ordinary transition, in particular $β_1 = 0.80 \pm 0.01$, are found to be robust against these perturbations.

cond-mat↗

arXiv1997

Surface critical behavior of two-dimensional dilute Ising models

Ising models with nearest-neighbor ferromagnetic random couplings on a square lattice with a (1,1) surface are studied, using Monte Carlo techniques and star-tiangle transformation method. In particular, the critical exponent of the surface magnetization is found to be close to that of the perfect model, beta_s=1/2. The crossover from surface to bulk critical properties is discussed.

cond-mat.dis-nn↗

arXiv1996

From microscopic description to statistical mechanics of Cu-O chain fragments in the high-Tc superconductors REBa_2Cu_3O_{6+x}

The oxygen deficient CuO_x planes of the high-Tc superconductors REBa_2Cu_3O_{6+x} (RE denotes a rare-earth atom or yttrium) are studied. Starting from the Emery model for the Cu-O chain fragments, an extended ASYNNNI model is proposed to describe the statistical mechanics of the CuO_x planes. The model is analysed by using Monte Carlo techniques, computing especially the charge transfer to the CuO$_2$ planes regulating the high-Tc superconductivity, and the concentration of differently coordinated Cu ions.Results are compared to experimental data for various RE cases.

cond-mat.supr-con↗