Graphene and graphene-like materials can host—at their edges—localized states whose properties can differ dramatically from those of bulk states. Three types of edge states have been established in these materials—zigzag, bearded, and armchair—named after their geometry. Now Daohong Song of Nankai University in China and collaborators have used a graphene-like photonic crystal to demonstrate the possibility of a fourth edge, called twig, with exotic topological features. The researchers suggest that twig edge states could exist in other honeycomb-lattice structures, broadening the options for realizing topologically protected energy transport via edge states in materials [1].
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