Yasui Tomoaki, Tutu Hiroki, Yamamoto Mariko, Fujisaka Hirokazu
Department of Applied Analysis and Complex Dynamical Systems, Graduate School of Informatics, Kyoto University, Japan.
Phys Rev E Stat Nonlin Soft Matter Phys. 2002 Sep;66(3 Pt 2A):036123. doi: 10.1103/PhysRevE.66.036123. Epub 2002 Sep 23.
The Ginzburg-Landau model for the anisotropic XY spin system in an oscillating magnetic field below the critical temperature T(c), psi;(r,t)=(T(c)-T)psi-/psi/(2)psi+gammapsi(*)+ nabla (2)psi+h cos(Omegat) is both theoretically and numerically studied. Here psi is the complex order parameter and gamma stands for the real anisotropy parameter. It is numerically shown that the spatially uniform system shows various characteristic oscillations (dynamical phases), depending on the amplitude h and the frequency Omega of the external field. As the control parameter, either h or Omega, is changed, there exist dynamical phase transitions (DPT), separating them. By making use of the mode expansion analysis, we obtain the phase diagrams, which turn out to be in a qualitative agreement with the numerically obtained ones. By carrying out the Landau expansion, the reduced equations of motion near the DPT are derived. Furthermore, taking into account the spatial variation of order parameters, we will derive the analytic expressions for domain walls, which are represented by the Néel and Bloch type walls, depending on the difference of the coexistence of phases.
研究了在低于临界温度(T(c))的振荡磁场中各向异性XY自旋系统的金兹堡 - 朗道模型，(\psi(r,t)=(T(c)-T)\psi-\frac{\vert\psi\vert^2}{2}\psi+\gamma\psi*+\nabla^2\psi+h\cos(\Omega t))，采用了理论和数值研究方法。这里(\psi)是复序参量，(\gamma)代表实各向异性参量。数值结果表明，空间均匀系统呈现出各种特征振荡（动力学相），这取决于外场的振幅(h)和频率(\Omega)。当控制参数(h)或(\Omega)变化时，存在动力学相变（DPT）将它们分开。通过模式展开分析，我们得到了相图，结果与数值得到的相图在定性上一致。通过进行朗道展开，推导了DPT附近的约化运动方程。此外，考虑序参量的空间变化，我们将推导畴壁的解析表达式，根据相共存的差异，畴壁由奈尔型和布洛赫型壁表示。
