Two-step Transition in 2D Melting of Hard-Core Soft-Shell Colloidal Particles

In contrast to the 3D melting, where transitions primarily occur between solid and liquid phases, 2D melting is characterized by a two-step transition through an intermediate hexatic phase. Although the Kosterlitz–Thouless–Halperin–Nelson–Young (KTHNY) theory postulates two successive continuous transitions-from solid to hexatic, then to liquid--driven by the unbinding of topological defects, the precise 2D melting mechanism and the influence of the interaction potential between colloidal particles remain subjects of ongoing debate. This uncertainty is largely attributed to the extended interaction ranges characteristic of soft potentials, necessitating the study of extensive system sizes for a comprehensive understanding. In our study, we explore the melting scenario of a 2D Hard-Core Soft-Shell particle system. Using Molecular Dynamics simulations on a system encompassing over a million particles, we employed a range of analysis techniques, including Bond Orientation Order, Structure Factor, Entropy, and Positional Correlation to elucidate the melting process. Through our analysis of defect distribution, we pinpointed the expansive hexatic phase region observed in HCSS colloidal systems.