Attraction Tames Two-Dimensional Melting: From Continuous to Discontinuous Transitions

Area of Science:

• Condensed matter physics
• Statistical mechanics
• Materials science

Background:

• Two-dimensional systems can exhibit a hexatic phase, but their phase diagrams and transitions are complex.
• The influence of attractive forces on these transitions, common in molecular and colloidal systems, remains largely speculative.
• Recent progress has clarified phase diagrams for hard disks, polygons, and inverse power-law potentials.

Purpose of the Study:

• To investigate the role of attractive forces in the melting behavior of two-dimensional systems.
• To determine if attractive forces alter the existence of the hexatic phase during melting.
• To explore the interplay between system shape and attractive forces in phase transitions.

Main Methods:

• Numerical simulations were employed to model two-dimensional systems.
• Lennard-Jones particles and attractive polygons were simulated to observe melting behavior.
• Phase diagrams were analyzed across various temperature ranges to identify distinct melting scenarios.

Main Results:

• Attractive forces promote a discontinuous melting scenario, completely suppressing the hexatic phase.
• At high temperatures, systems follow shape-dependent melting, similar to hard-particle models.
• At low temperatures, all simulated systems exhibit first-order transitions without a hexatic phase, dominated by attractive forces.

Conclusions:

• Attractive forces fundamentally alter melting in two-dimensional systems by eliminating the hexatic phase.
• The temperature-dependent dominance of shape or attraction dictates the melting pathway.
• Colloidal experiments can tune attractive forces to observe diverse melting scenarios within the same system.