12 research outputs found
Quantum Lattice Solitons
The number state method is used to study soliton bands for three anharmonic
quantum lattices: i) The discrete nonlinear Schr\"{o}dinger equation, ii) The
Ablowitz-Ladik system, and iii) A fermionic polaron model. Each of these
systems is assumed to have -fold translational symmetry in one spatial
dimension, where is the number of freedoms (lattice points). At the second
quantum level we calculate exact eigenfunctions and energies of pure
quantum states, from which we determine binding energy , effective
mass and maximum group velocity of the soliton bands as
functions of the anharmonicity in the limit . For arbitrary
values of we have asymptotic expressions for , , and
as functions of the anharmonicity in the limits of large and small
anharmonicity. Using these expressions we discuss and describe wave packets of
pure eigenstates that correspond to classical solitons.Comment: 21 pages, 1 figur
Microscopic Non-Universality versus Macroscopic Universality in Algorithms for Critical Dynamics
We study relaxation processes in spin systems near criticality after a quench
from a high-temperature initial state. Special attention is paid to the stage
where universal behavior, with increasing order parameter emerges from an early
non-universal period. We compare various algorithms, lattice types, and
updating schemes and find in each case the same universal behavior at
macroscopic times, despite of surprising differences during the early
non-universal stages.Comment: 9 pages, 3 figures, RevTeX, submitted to Phys. Rev. Let
Effect of the vacancy interaction on antiphase domain-growth in a two-dimensional binary alloy
The influence of diffusing vacancies on the antiphase domain growth process in a binary alloy is studied by Monte Carlo simulations. The system is modelled by means of a Blume-Emery-Griffiths hamiltonian with a biquadratic coupling parameter K controlling the microscopic interactions between vacancies. We obtain that, independently of K, the vacancies exhibit a tendency to concentrate on the antiphase boundaries. This gives rise to an effective interactions between movin interfaces and diffusing vacancies which strongly influences the domain growth process. One distinguishes three different behaviours: i) for K 1 the growth is slown down but still curvature driven