Phase Transitions of Soft Disks in External Periodic Potentials: A Monte Carlo Study

TL;DR

This study uses Monte Carlo simulations to explore phase transitions of soft disks in a periodic external potential, revealing reentrant melting behavior and supporting a dislocation unbinding theory of laser-induced melting.

Contribution

It provides detailed phase diagrams and finite size scaling analysis of colloid-like particles under external fields, highlighting reentrant melting and confirming theoretical predictions.

Findings

Reentrant liquid phase observed over a broad parameter range

System behavior similar to charge stabilized colloids undergoing re-melting

Data supports dislocation unbinding theory of laser-induced melting

Abstract

The nature of freezing and melting transitions for a system of model colloids interacting by a DLVO potential in a spatially periodic external potential is studied using extensive Monte Carlo simulations. Detailed finite size scaling analyses of various thermodynamic quantities like the order parameter, its cumulants etc. are used to map the phase diagram of the system for various values of the reduced screening length $\kappa a_{s}$ and the amplitude of the external potential. We find clear indication of a reentrant liquid phase over a significant region of the parameter space. Our simulations therefore show that the system of soft disks behaves in a fashion similar to charge stabilized colloids which are known to undergo an initial freezing, followed by a re-melting transition as the amplitude of the imposed, modulating field produced by crossed laser beams is steadily increased. Detailed analysis of our data shows several features consistent with a recent dislocation unbinding theory of laser induced melting.