Competing length scales and symmetry frustration govern nonuniversal melting in two-dimensional core-softened colloidal crystals.

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 uncover and analyze distinct melting pathways for three polymorphic solid phases: a low-density triangular (LDT) lattice, a stripe phase, and a kagome crystal. 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 intrastripe mobility persists, consistent with a Kosterlitz-Thouless-Halperin-Nelson-Young-like scenario. These findings demonstrate that melting in two-dimensional soft-matter systems is inherently nonuniversal 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.