Kim Jeongmin, Kim Chanjoong, Sung Bong June
Department of Chemistry, Sogang University, Seoul 121-742, Republic of Korea.
Chemical Physics Interdisciplinary Program and Liquid Crystal Institute, Kent State University, Kent, OH 44242, USA.
Phys Rev Lett. 2013 Jan 25;110(4):047801. doi: 10.1103/PhysRevLett.110.047801. Epub 2013 Jan 24.
A two-dimensional (2D) solid lacks long-range positional order and is diffusive by means of the cooperative motion of particles. We find from molecular dynamics simulations of hard discs that 2D colloids in solid and hexatic phases show seemingly Fickian but strongly heterogeneous dynamics. Beyond translational relaxation time, the mean-square displacement is linear with time, t, implying that discs would undergo Brownian diffusion and the self-part of the van Hove correlation function [G(s)(r,t)] might be Gaussian. But dynamics is still heterogeneous and G(s)(r,t) is exponential at large r and oscillatory with multiple peaks at intermediate length. We attribute the existence of several such peaks to the observation that there are several clusters of discs with discretized mobility. The cluster of marginally mobile discs grows with time and begins to percolate around translational relaxation time while clusters of fast discs emerge in the middle of the marginally mobile cluster.
二维（2D）固体缺乏长程位置有序性，并且通过粒子的协同运动而具有扩散性。我们从硬圆盘的分子动力学模拟中发现，处于固相和六方相的二维胶体表现出看似菲克型但强烈非均匀的动力学。在平移弛豫时间之后，均方位移与时间t呈线性关系，这意味着圆盘将经历布朗扩散，并且范霍夫关联函数[G(s)(r,t)]的自部分可能是高斯型的。但动力学仍然是非均匀的，并且G(s)(r,t)在大r时是指数型的，在中间长度处有多个峰值且呈振荡状。我们将几个这样的峰值的存在归因于这样的观察结果：存在几个具有离散迁移率的圆盘簇。边缘可移动圆盘的簇随时间增长，并在平移弛豫时间左右开始渗流，而快速圆盘的簇出现在边缘可移动簇的中间。
