Metastable states in the J_{1}-J_{2} Ising model.

We study the J_{1}-J_{2} Ising model on the square lattice using the random local field approximation (RLFA) and Monte Carlo (MC) simulations for various values of the ratio p=J_{2}/|J_{1}| with antiferromagnetic coupling J_{2}, ensuring spin frustration. RLFA predicts metastable states with zero order parameter (polarization) at low temperature for p∈(0,1). This is supported by our MC simulations, in which the system relaxes into metastable states with not only zero, but also with arbitrary polarization, depending on its initial value, external field, and temperature. We support our findings by calculating the energy barriers of these states at the level of individual spin flips relevant to the MC calculation. We discuss experimental conditions and compounds appropriate for experimental verification of our predictions.

Phase mixing, induced relaxation, and chaos in one-dimensional dynamical systems.

This paper investigates the mechanism of induced phase mixing, which leads to effective dissipation in classical nonlinear dynamical systems with a fast modulation of the potential. The suggested model can be applied to a classical dynamical description of cold atomic clouds in optical traps. We show that the parametric nonadiabatic modulation of the laser intensity can provide a tool for dynamical control of the effective relaxation in such systems.