Structure And Dynamics In Two-dimensional Colloidal Crystal Melting

The nature of melting transition is an important and fundamental problem in condensedmatter physics. Since the last century, it has been widely debated whether thetwo-dimensional melting undergoes a first-order transition as in three-dimensional meltingor a two-step continuous transition as developed by Kosterlitz-Thouless-Halperin-Nelson-Young (KTHNY). Over the years, amount of computer simulations and experiments havebeen consistent with KTHNY theory. The static structure and order parameters havereceived extensive study in previous work, but dynamics during the melting are relativelyless. Here, we perform simulations of2D soft purely repulsive systems to study both thestructure and dynamics of melting. Our simulation results are consistent with thepredictions of KTHNY theory that we find an intermediate hexatic phase between crystaland liquid phase. In our system, hexatic phase has strong dynamical heterogeneities whichexhibit a nonmonotonic trend. Interestingly, the string-like structures of cooperativeparticles are observed in hexatic phase. It is well known that the string-like structures arerearrangements regions occurred via the cooperative motion of spatially clustered particlesin supercooled or glass-forming liquids. In our view, these special structures of cooperativeparticles play an important role in melting behavior. Moreover, we study the melting ofmixtures of soft and hard particles system. The cooperative motion regions show strongspatial correlation with defect clusters.