Bond-orientational Order in Melting of Colloidal Crystals

TL;DR

This study uses Brownian dynamics simulations to analyze bond-orientational order during melting in colloidal systems, confirming the existence of a hexatic phase in 2D and contrasting melting behaviors in 2D and 3D.

Contribution

It provides the first detailed simulation-based comparison of melting processes and bond-orientational order in 2D and 3D colloidal systems with Yukawa interactions.

Findings

Confirmation of a two-stage melting process in 2D with a hexatic phase.

In 3D, local order breakdown occurs throughout the system simultaneously.

Distinct melting mechanisms are observed between 2D and 3D colloidal systems.

Abstract

Using Brownian dynamics simulation, we study the orientational order in melting transition of colloidal systems with $'$soft$'$ Yukawa potential. The bond-orientational order parameter $\Phi_{6}$ and the bond-orientational order function $g_B(r)$ are calculated in two-dimensional systems. It is found that a two-stage transition and the hexatic phase are indeed existent in two-dimensional melitng, which is consistent with the prediction of the Kosterlitz-Thouless-Halperin-Nelson-Young theory. For comparing with the melting process in three-dimensional systems, the probability distribution of single-particle local order parameter is introduced. Based on the extensive simulations, it is qualitatively suggested that the breakdown of local order only occurs on the fractional part of the colloidal systems for the two-dimensional melting, but in three-dimensional melting, this breakdown takes place on the whole systems at the same time.