# Observing one-step melting pathway in two-dimensional hard circular particle system

## TL;DR

This study reveals that the melting behavior of two-dimensional hard disk systems depends on particle size, showing either a one-step or two-step melting pathway.

## Contribution

The discovery of a tunable, non-equilibrium one-step melting pathway in large particle systems challenges previous understanding of 2D melting.

## Key findings

- Large size particles exhibit a one-step melting pathway due to metastable configurations.
- The one-step pathway is a non-equilibrium phase transition linked to cage dynamics.
- Melting behavior is tunable by adjusting particle size.

## Abstract

The nature of two-dimensional melting remains a matter of debate. Based on Langevin dynamics simulation, we present a surprising observation that the melting pathway of hard circular-particles/disks is relevant to the dynamical properties of particles. Using hard circular-particles/disks, where particle friction is proportional to particle size, results show the melting pathway of small size particles obeys two-step scenario, consistent with previous reports on melting behavior of hard disks. Conversely, in large size particle systems, we observe a one-step melting pathway. Further investigation reveals that the emergent one-step melting pathway is non-equilibrium phase transition that relates to cooperative relaxation of cage dynamics. This originates from the particularly stable/stiff configuration in large size particle system, which is a metastable state arrested by changed dynamics of particles, thus inducing a non-equilibrium melting pathway that distinguishes from the equilibrium melting behavior. Our findings shed light on the debate on melting behavior of hard disks.

•The melting process relates to the cooperative relaxation of cage dynamics•Non-equilibrium one-step melting pathway is observed in 2D hard circular particle systems•The non-equilibrium melting pathway originates from the metastable state arrested by dynamics•The melting pathway is tunable through the size of particle

The melting process relates to the cooperative relaxation of cage dynamics

Non-equilibrium one-step melting pathway is observed in 2D hard circular particle systems

The non-equilibrium melting pathway originates from the metastable state arrested by dynamics

The melting pathway is tunable through the size of particle

Condensed matter physics