Structure And Dynamics Of Melting In Two-Dimensional Granular Crystal

The investigation of structure and dynamics are key approaches for understanding the essence of phase transition. Here, we investigate the structure and dynamics of two-dimensional melting in granular system. In previous studies of two-dimensional melting, structural properties have received extensive attentions. For example, the classical theory of two-dimensional melting, KTHNY theory, is based on the analysis of structural defects. However, less studies are focused on the dynamics in two-dimensional melting. In this thesis, we study the structure and dynamics in two-dimensional granular system, which driven by an air-fluidized setup. Structurally, we find that the melting process is in agreement with the prediction of KTHNY theory. The melting proceeds in two steps, first from a long range orientational ordered crystal to a quasi-long range orientational ordered hexatic phase, then from a hexatic phase to a liquid phase. Dynamically, strong dynamical heterogeneity has been found in the hexatic phase, which manifest itself in the form of cooperative rearrangements. By close comparison of structural defects and velocity distribution, we found the fast moving regions are coincident with local defect structures. In conclusion, the two-dimensional melting in granular system, although is a far from equilibrium system, shows great similarity with equilibrium systems. On the other hand, the analysis of dynamics shed new light on the study of dynamical heterogeneity in glassy systems.