Melting and re-entrant melting of polydisperse hard disks

TL;DR

This study uses large-scale simulations to explore how polydispersity affects melting in 2D hard disks, revealing re-entrant melting and a shift in transition mechanisms, highlighting fundamental differences from 3D systems.

Contribution

It demonstrates that increasing polydispersity changes the melting process and introduces re-entrant melting in 2D, contrasting with 3D behaviors.

Findings

Re-entrant melting observed in high-density 2D polydisperse disks.

Melting transition mechanism shifts with increasing polydispersity.

Significantly enlarged stability range for hexatic phase in 2D.

Abstract

Because of long-wavelength fluctuations, the nature of solids and phase transitions in 2D are different from those in 3D systems, and have been heavily debated in past decades, in which the focus was on the existence of hexatic phase. Here, by using large scale computer simulations, we investigate the melting transition in 2D systems of polydisperse hard disks. We find that, with increasing the particle size polydispersity, the melting transition can be qualitatively changed from the recently proposed two-stage process to the Kosterlitz-Thouless-Halperin-Nelson-Young scenario with significantly enlarged stability range for hexatic phase. Moreover, re-entrant melting transitions are found in high density systems of polydisperse hard disks, which were proven impossible in 3D polydisperse hard-sphere systems. These suggest a new fundamental difference between phase transitions in polydisperse systems in 2D and 3D.