Physical Review E (2015). doi:10.1103/PhysRevE.92.012324
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Soft-core particles freezing to form a quasicrystal and a crystal-liquid phase

A.J. Archer (1), A.M. Rucklidge (2) and E. Knobloch (3)

(1) Department of Mathematical Sciences, Loughborough University, Loughborough, Leicestershire, LE11 3TU, UK
(2) Department of Applied Mathematics, University of Leeds, Leeds, LS2 9JT, UK
(3) Department of Physics, University of California, Berkeley, CA 94720-7300, USA

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.

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