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

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.

SI included

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• Two-Dimensional Melting of two- and three-component mixtures
• The Liquid--Hexatic Transition for Soft Disks
• Emergent Mesoscale Correlations in Active Solids with Noisy Chiral Dynamics
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• Learning phase transitions from regression uncertainty: A new regression-based machine learning approach for automated detection of phases of matter
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• Long-wavelength fluctuations and dimensionality crossover in confined liquids
• Hexatic Phase in Covalent Two-Dimensional Silver Iodide
• Data-driven criterion for the solid-liquid transition of two-dimensional self-propelled colloidal particles far from equilibrium