Ground states of colloidal molecular crystals on periodic substrates

TL;DR

This paper investigates the ground state configurations of colloidal molecular crystals with dimers and trimers on square and triangular lattices, revealing complex ordering patterns and discussing modeling assumptions.

Contribution

It provides detailed simulation results on colloidal ground states and critiques previous simplified spin model mappings.

Findings

Identification of bipartite and quadripartite orderings

Discussion of limitations in rigid object assumptions

Insights into complex colloidal arrangements

Abstract

Two dimensional suspensions of spherical colloids subject to periodic external fields exhibit a rich variety of molecular crystalline phases. We study in simulations the ground state configurations of dimeric and trimeric systems, that are realized on square and triangular lattices, when either two or three macroions are trapped in each external potential minimum. Bipartite orders of the checkerboard or stripe types are reported together with more complex quadripartite orderings, and the shortcomings of envisioning the colloids gathered in a single potential minimum as a composite rigid object are discussed. This work also sheds light on simplifying assumptions underlying previous theoretical treatments and that made possible the mapping onto spin models.