Heterogeneous dynamics in polycrystal and glass in a binary mixture with changing size dispersity and composition.

Using molecular dynamics simulation we investigate the dynamics in a two-dimensional binary mixture at a low temperature and at high densities. We increase the size ratio of the diameters of the two components or the fraction of the larger particles. Then changeovers occur from polycrystal to glass with proliferation of defects. The relationship between the degree of disorder and the slow dynamics is studied by simultaneous visualization of a disorder variable D{j} introduced in our previous paper T. Hamanaka and A. Onuki[Phys. Rev. E 74, 011506 (2006)] and the particle displacement Deltar{j} in a long time interval. In polycrystal, the particles in the grain boundary regions have large D{j} and a relatively large mobility, producing significant dynamic heterogeneity on long time scales. In the crossover from polycrystal to glass, the crystalline regions become narrow, but the particles with relatively large D{j} still trigger the formation of chainlike particle motions, leading to the dynamic heterogeneity.