Onset of stripe order in classical fluids: Lessons from lattice-gas mixtures

TL;DR

This study investigates how classical lattice-gas mixtures can spontaneously form stripe patterns under various interaction conditions, revealing that stripe order is more common and can arise from diverse interaction types, with implications for materials science.

Contribution

The paper demonstrates that stripe order can emerge from a wide range of spherically symmetric interactions in classical fluids, expanding understanding of pattern formation mechanisms.

Findings

Stripes can form from different combinations of repulsive and attractive interactions.

Various other patterns like crystals and networks also emerge.

Stripe formation is more prevalent than previously thought.

Abstract

When two molecular species with mutual affinity are mixed together, various self-assembled phases can arise at low temperature, depending on the shape of like and unlike interactions. Among them, stripes -- where layers of one type are regularly alternated with layers of another type -- hold a prominent place in materials science, occurring e.g. in the structure of superconductive doped antiferromagnets. Stripe patterns are relevant for the design of functional materials, with applications in optoelectronics, sensing, and biomedicine. In a purely classical setting, an open question pertains to the features that spherically-symmetric particle interactions must have to foster stripe order. Here we address this challenge for a lattice-gas mixture of two particle species, whose equilibrium properties are exactly determined by Monte Carlo simulations with Wang-Landau sampling, in both planar and spherical geometry, and for equal chemical potentials of the species. Somewhat surprisingly, stripes can emerge from largely different off-core interactions, featuring various combinations of repulsive like interactions with a predominantly attractive unlike interaction. In addition to stripes, our survey also unveils crystals and crystal-like structures, cluster crystals, and networks, which considerably broaden the catalog of possible patterns. Overall, our study demonstrates that stripes are more widespread than generally thought, as they can be generated by several distinct mechanisms, thereby explaining why stripe patterns are observed in systems as diverse as cuprate materials, biomaterials, and nanoparticle films.