含空位序的扩展J1 - J2模型中有限温度磁相变的动力学研究
Dynamic approach to finite-temperature magnetic phase transitions in the extended J1- J2 model with vacancy order
摘要：
最近发现的铁基超导体APDMATHABMM Fe $_{2-x}$ Se $_{2}$（$A$ =K，Rb，Cs，Tl）显示出长程反铁磁有序，具有意想不到的高转变温度$T_N \sim 550$ K和独特的$\sqrt{5} \times \sqrt{5}$空位有序。以扩展的$J_1$ - $J_2$模型为最小模型，采用大规模Monte Carlo方法研究了含有$\sqrt{5} \times \sqrt{5}$空位超结构的正方晶格中的有限温度磁相变.利用平行回火技术，在三组代表性的模型参数下，检测到块自旋棋盘和条纹反铁磁态为基态。采用短时动态法精确地确定了临界温度以及静态和动态指数。我们的研究结果表明，在实验中观察到的临界温度的显着提高应主要是由于空位顺序和块晶格收缩的组合效应。
英文摘要：
The recently discovered iron-based superconductors A$_{y}$Fe$_{2-x}$Se$_{2}$ ($A$=K, Rb, Cs, Tl) show a long-range antiferromagnetic order with an unexpected high transition temperature $T_N \sim 550$ K and a unique $\sqrt{5} \times \sqrt{5}$ vacancy order. Taking the extended $J_1$-$J_2$ model as a minimal model, we investigate the finite-temperature magnetic phase transitions in a square lattice with a $\sqrt{5} \times \sqrt{5}$ vacancy superstructure by using large-scale Monte Carlo simulations. By the parallel tempering technique, the block spin checkerboard and stripe antiferromagnetic states are detected to be the groundstates for three representative sets of model parameters. The short-time dynamic approach is applied to accurately determine the critical temperature as well as the static and dynamic exponents. Our results indicate that the dramatic enhancement of the critical temperature as observed in experiments should be mainly due to a combination effect of the vacancy order and the block lattice contraction.
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