Takamoto M

Nonequilibrium dynamic phase transition in the ferromagnetic potts model

The nonequilibrium dynamic phase transition arises in various magnetic systems such as ferromagnetic Ising model when system is driven by both an external field and temperature simultaneously. In this paper, the nonequilibrium dynamic phase transition in the q-state Potts model in the presence of a time dependent oscillating magnetic field on a simple cubic lattice is investigated by mean field theory and time dependent Ginzburug-Landau equation. For the case of q = 2, with decrease of the temperature the system undergoes a dynamically ordered phase transition, which is characterized by the period averaged magnetization Q, from a dynamically disordered state Q = 0 to the dynamically ordered state Q ≠ 0. On the other hand, for the case of q = 3 the system has indicated more complicated behavior than that of q = 2. We investigated those characteristic features of the dynamical phase state from the behavior of the dynamic magnetization and the Liapunov exponent.

Monte Carlo simulation of the one-dimensional N-state clock model with long range inverse square interaction

Using Monte Carlo simulation, the one dimensional N-state clock model with long range inverse square interaction has been studied. In the case of N = 6, the temperature dependence of the specific heat shows two peaks at T1 and T2 (< T1). The critical exponent η calculated from the system size dependence of magnetization changes with temperature in the region between T1 and T2. The behaviors are very similar to those of the two-dimensional 6-state clock model with the nearest neighbor interaction which shows two steps of phase transition, Berezinskii-Kosterlitz-Thouless transition and ordinary long range order. We have also confirmed that the temperature T2 shift toward zero with the increase of N.