Self-Assembly of a Colloidal Honeycomb Crystal in Silico for Topological Valley Photonics

The quest to employ colloidal self-assembly as a scalable means of fabricating photonic crystals with a complete photonic band gap at optical frequencies has proved challenging throughout the first quarter of the 21st century. Meanwhile, the field of topological photonics has emerged, presenting new, and largely unexploited, functionalities for self-assembled colloidal materials. The robustness of topological photonic properties to defects that are practically unavoidable in self-assembled colloidal structures appears to be especially attractive. Here, the self-assembly of a colloidal honeycomb crystal is demonstrated in computer simulations, with an assembly strategy that not only suppresses the formation of real-space topological defects observed in experiments but also results in topological photonic properties in reciprocal space. This assembly strategy promotes the emergence of long-range order and allows for the breaking of spatial inversion symmetry with two distinct sub-lattices. A sufficient dielectric contrast between the colloidal particles sitting on these two sub-lattices is exploited to realize a valley-Hall topological photonic phase, allowing for unidirectional propagation of circularly polarized light through waveguides composed of the designer crystals. The design rules are tested for their robustness to open the door to scalable fabrication of topological photonic devices via colloidal self-assembly.