Novel Low-Temperature Behavior in Classical Many-Particle Systems

TL;DR

This paper reveals unexpected low-temperature phenomena in classical many-particle systems with soft interactions, including vanishing frequencies and negative thermal expansion, linked to the energy landscape's topography.

Contribution

It uncovers novel low-temperature behaviors and the role of energy landscape topography in classical many-particle systems with soft interactions.

Findings

Large fraction of normal-mode frequencies vanish at certain densities

Lattice ground states have more vanishing frequencies than disordered states

Negative thermal expansion observed during melting transition

Abstract

We show that classical many-particle systems interacting with certain soft pair interactions in two dimensions exhibit novel low-temperature behaviors. Ground states span from disordered to crystalline. At some densities, a large fraction of normal-mode frequencies vanish. Lattice ground-state configurations have more vanishing frequencies than disordered ground states at the same density and exhibit vanishing shear moduli. For the melting transition from a crystal, the thermal expansion coefficient is negative. These unusual results are attributed to the topography of the energy landscape.