Self-Assembled Honeycomb Lattices of Dielectric Colloidal Nanospheres Featuring Photonic Dirac Cones

The prime example of a two-dimensional photonic crystal featuring Dirac cones is based on the honeycomb lattice. Colloidal self-assembly can produce a two-dimensional colloidal structure over a large area but is limited to hexagonal-close-packed structures. Therefore, it has been challenging to fabricate honeycomb monolayers by colloidal self-assembly. Here, we fabricate a dielectric honeycomb lattice in a large area by template-assisted self-assembly and analyze its photonic structure. Although the Dirac point occurring at the K point is not accessible by light in free space, a part of the upper Dirac cone above the light line is verified by a Fourier analysis of the back-focal-plane image. Because the template-assisted self-assembly enables additional geometrical perturbations in the honeycomb lattice, various lattices can be fabricated. This additional degree of freedom may provide an alternative way of fabricating photonic topological insulators.