Soft-core particles freezing to form a quasicrystal and a crystal-liquid phase

TL;DR

This study explores how soft-core particles with a two-scale potential can form novel phases, including a crystal-liquid state and a 12-fold quasicrystal, through dynamical density functional theory and simulations.

Contribution

It introduces the discovery of a crystal-liquid phase and a quasicrystalline state in soft-core particle systems with two-scale interactions, highlighting their formation mechanisms.

Findings

Identification of a crystal-liquid state with coexisting liquid and lattice particles

Observation of a 12-fold quasicrystalline phase in the system

Revelation of a nonlinear dynamical process leading to quasicrystal formation

Abstract

Systems of soft-core particles interacting via a two-scale potential are studied. The potential is responsible for peaks in the structure factor of the liquid state at two different but comparable length scales, and a similar bimodal structure is evident in the dispersion relation. Dynamical density functional theory in two dimensions is used to identify two novel states of this system, the crystal-liquid state, in which the majority of the particles are located on lattice sites but a minority remains free and so behaves like a liquid, and a 12-fold quasicrystalline state. Both are present even for deeply quenched liquids and are found in a regime in which the liquid is unstable with respect to modulations on the smaller scale only. As a result the system initially evolves towards a small scale crystal state; this state is not a minimum of the free energy, however, and so the system subsequently attempts to reorganize to generate the lower energy larger scale crystals. This dynamical process generates a disordered state with quasicrystalline domains, and takes place even when this large scale is linearly stable, i.e., it is a nonlinear process. With controlled initial conditions a perfect quasicrystal can form. The results are corroborated using Brownian dynamics simulations.