Proliferation of anomalous symmetries in colloidal monolayers subjected to quasiperiodic light fields

TL;DR

This study investigates why certain symmetries, like 7-fold, are absent in quasicrystals by examining colloidal particles in quasiperiodic laser fields, revealing geometrical constraints and motif distributions affecting quasicrystal formation.

Contribution

It demonstrates geometrical constraints impede 7-fold symmetry quasicrystal formation and links motif density to the absence of specific symmetries in atomic quasicrystals.

Findings

Quasicrystals form more easily with 5-fold symmetry than 7-fold.

Highly symmetric motifs are less frequent in 7-beam laser patterns.

Motif deficiency may explain the absence of certain symmetries in atomic quasicrystals.

Abstract

Quasicrystals provide a fascinating class of materials with intriguing properties. Despite a strong potential for numerous technical applications, the conditions under which quasicrystals form are still poorly understood. Currently, it is not clear why most quasicrystals hold 5- or 10-fold symmetry but no single example with 7 or 9-fold symmetry has ever been observed. Here we report on geometrical constraints which impede the formation of quasicrystals with certain symmetries in a colloidal model system. Experimentally, colloidal quasicrystals are created by subjecting micron-sized particles to two-dimensional quasiperiodic potential landscapes created by n=5 or seven laser beams. Our results clearly demonstrate that quasicrystalline order is much easier established for n = 5 compared to n = 7. With increasing laser intensity we observe that the colloids first adopt quasiperiodic order at local areas which then laterally grow until an extended quasicrystalline layer forms. As nucleation sites where quasiperiodicity originates, we identify highly symmetric motifs in the laser pattern. We find that their density strongly varies with n and surprisingly is smallest exactly for those quasicrystalline symmetries which have never been observed in atomic systems. Since such high symmetry motifs also exist in atomic quasicrystals where they act as preferential adsorption sites, this suggests that it is indeed the deficiency of such motifs which accounts for the absence of materials with e.g. 7-fold symmetry.