Attraction tames two-dimensional melting: from continuous to discontinuous transitions

TL;DR

This study uses numerical simulations to show that attractive forces in two-dimensional systems lead to a discontinuous melting transition without a hexatic phase, contrasting with purely shape-driven melting.

Contribution

It reveals how attraction influences 2D melting, demonstrating a shift from continuous to discontinuous transitions and highlighting the temperature-dependent role of attractions.

Findings

Attraction induces a first-order melting transition without a hexatic phase.

High-temperature melting follows shape-dominated scenarios similar to hard particles.

Intermediate temperature melting varies depending on particle shape.

Abstract

Two-dimensional systems may admit a hexatic phase and hexatic-liquid transitions of different natures. The determination of their phase diagrams proved challenging, and indeed those of hard-disks, hard regular polygons, and inverse power-law potentials, have been only recently clarified. In this context, the role of attractive forces is currently speculative, despite their prevalence at both the molecular and colloidal scale. Here we demonstrate, via numerical simulations, that attraction promotes a discontinuous melting scenario with no hexatic phase. At high-temperature, Lennard-Jones particles and attractive polygons follow the shape-dominated melting scenario observed in hard-disks and hard polygons, respectively. Conversely, all systems melt via a first-order transition with no hexatic phase at low temperature, where attractive forces dominate. The intermediate temperature melting scenario is shape-dependent. Our results suggest that, in colloidal experiments, the tunability of the strength of the attractive forces allows for the observation of different melting scenario in the same system.