Competing Length Scales and Symmetry Frustration Govern Non-Universal Melting in 2D Core-softened Colloidal Crystals

TL;DR

This study reveals that melting in 2D colloidal crystals with competing interaction scales is non-universal, governed by symmetry, frustration, and multiple length scales, with distinct pathways for different crystal phases.

Contribution

It uncovers how competing length scales and symmetry frustration lead to diverse melting behaviors in 2D colloidal crystals, expanding understanding beyond classical theories.

Findings

Triangular and kagome crystals melt via first-order transitions.

Stripe phase exhibits a continuous, KTHNY-like melting transition.

Melting pathways depend on lattice symmetry and interaction scale competition.

Abstract

We investigate the melting behavior of two-dimensional colloidal crystals stabilized by a core-softened potential featuring two competing interaction length scales. Using molecular dynamics simulations, we analyze three polymorphic solid phases -- low-density triangular, stripe, and kagome -- and uncover distinct melting pathways. The triangular and kagome crystals undergo abrupt first-order transitions, driven by the interplay between energetic frustration and structural reorganization. In particular, the LDT phase melts through a sharp transition induced by a crossover between the two characteristic length scales. In contrast, the stripe phase exhibits a continuous transition with liquid-crystalline features: orientational and translational order decay gradually, while intra-stripe mobility persists, consistent with a KTHNY-like scenario. These findings demonstrate that melting in 2D soft-matter systems is inherently non-universal and governed by the competition between lattice symmetry, frustration, and multiple interaction scales. Our results provide microscopic insight into melting mechanisms beyond classical universality classes and offer guiding principles for the design of self-assembled materials with tunable phase behavior.