三维动态Ising模型中的非平衡相变:三临界点的存在

用Monte Carlo方法模拟了三维动态Ising模型中的非平衡相变,用统计的观点研究了序参量的大小和分布以描述该相变过程.保持温度和外场频率不变,改变外场大小使之由小到大变化,序参量由非零值变成零值.在低温阶段,序参量呈非连续变化,为典型的非连续相变,在高温阶段,序参量呈连续变化,为典型的连续相变.本文确定了界定非平衡转变的相界,并进一步确定了相界上区分非连续连续相变的三临界点.外场频率ω减小时,三临界点温度T_TCP向高温部分移动,并满足T_TCP=1.33×关键词：动态相变Ising模型三临界点

DYNAMICAL TRANSITION ANDTRICRITICAL POINTS OF 3D KINETIC ISING SPIN SYSTEM

The dynamic phase transition has been studied in the three-dimensional kinetic Ising model in the presence of a time-varying(sinusoidal)magnetic field by Monte Carlo simulation.The nature of the transition is characterized by studying the distribution of the order parameter.The system is in contact with an isothermal heat bath at temperature T.We varied the magnitude of the magnetic field,keeping the frequency of the magnetic field unchanged.For the lower values of the environment temperature the transition is discontinuous and it is continuous for higher values of the environment temperature,indicating the existence of a tricritical point (TCP) on the phase boundary.The TCP shifts towards higher temperature region with the decrease of frequency.i.e:TTCP=1.33×e(-ω/30.7)