Experimental antiferromagnetic tetratic phase in confined quasi-2d hard-sphere system with depletants

In this work, we experimentally demonstrate the self-assembly of a topologically ordered phase in a simple buckled system of colloidal spheres, i.e., without introduction of surface patterning or aspherical particles. Specifically, we realize an antiferromagnetic tetratic phase of hard-sphere, micron size polystyrene particles; the interparticle interactions of this system can be tuned using temperature-sensitive rod-like depletants made from the surfactant C₁₂E₆. We examine the topological order of the tetratic phase arising from the antiferromagnetic character of the system. We study the dislocations, in particular the presence/absence of single lattice dislocations which have been argued to be forbidden in the presence of strong antiferromagnetic interactions [D. Abutbul and D. Podolsky, Topological Order in an Antiferromagnetic Tetratic Phase, Phys. Rev. Lett. 128, 255501 (2022)].