Transient Structured Fluctuations in a Two-dimensional System with Multiple Ordered Phases

TL;DR

This study investigates transient structured fluctuations in a two-dimensional liquid system with multiple ordered phases, revealing how different symmetries dominate near phase transitions and how fluctuations relate to underlying phase structures.

Contribution

It provides detailed analysis of transient fluctuation structures in a complex 2D system with multiple phases, using aperture cross correlation functions to reveal symmetry-specific fluctuations.

Findings

Structured fluctuations with hexagonal symmetry appear near liquid-hexatic transitions.

Both hexagonal and square fluctuations occur across the liquid phase, depending on proximity to phase boundaries.

Ordered fluctuations are correlated with the structure of lower temperature phases even above transition temperatures.

Abstract

We report the structure of transient fluctuations in the liquid phase of a two-dimensional system that exhibits several ordered phases with different symmetries. The density-temperature phase diagram of the system studied, composed of particles with a repulsive shouldered soft-core pair interaction, has regions with stable liquid and hexatic phases, a square solid phase, two separate hexagonal solid phases and a quasi-crystalline phase with 12-fold symmetry. The structure of a fluctuation was determined by computing the same-time aperture cross correlation function of particle configurations. Along a low-temperature isotherm that intersects all the ordered phases we find that the liquid phase exhibits structured fluctuation with hexagonal symmetry near both liquid-hexatic transition lines. Along the same isotherm and in the stable liquid between the lower density hexatic-to-liquid and the higher density liquid-to-square solid transitions, we find that transient hexagonal ordered fluctuations dominate the liquid region near the hexatic-to-liquid transition and square ordered fluctuations dominate the liquid region near the liquid-to square solid transition, but that both structured fluctuations occur at all densities between these transition lines. At a higher temperature, at phase points in the liquid above but close to the density maximum of an underlying transition, there are ordered fluctuations that can be correlated with the structure of the lower temperature phase.