Inverse melting in lattice-gas models

Area of Science:

• Condensed Matter Physics
• Statistical Mechanics

Background:

• Inverse melting is a counterintuitive phenomenon observed in helium isotopes where crystals melt upon cooling at constant pressure.
• Understanding the fundamental mechanisms driving inverse melting is crucial for materials science and thermodynamics.

Purpose of the Study:

• To investigate discrete-space analogs of inverse melting using lattice-gas models.
• To explore the phase behavior and driving mechanisms of inverse melting in simplified systems.

Main Methods:

• Utilized transfer-matrix and Monte Carlo simulations.
• Employed low-temperature series expansions to reconstruct phase diagrams.
• Modeled systems with soft-core repulsion and short-ranged attraction on a triangular lattice.

Main Results:

• Observed phase behavior reminiscent of helium, including a loose-packed phase stable at low temperatures and pressures.
• Demonstrated the possibility of melting a close-packed solid through isobaric cooling.
• Identified geometrical factors, specifically the free-energy cost of vacancies, as the primary drivers of inverse melting.

Conclusions:

• The study successfully replicates key aspects of inverse melting in a discrete-space model.
• Geometrical considerations, rather than solely energetic ones, play a significant role in inverse melting.
• The findings offer insights into the fundamental physics of phase transitions and crystal behavior.