Observation of Topological Armchair Edge States in Photonic Biphenylene Network

Abstract Edge states in 2D materials are vital for advancements in spintronics, quantum computing, and logic transistors. For uniform graphene, it is well known that the zigzag edges can host edge states, but the realization of armchair edge states has been challenging without engineered strain or breaking the time‐reversal symmetry. Here, by using a photonic analog of a recently synthesized graphene‐like biphenylene network (BPN), topological in‐gap edge states are demonstrated, particularly at the armchair edges. Interestingly, several bulk states preserve the characteristics of edge states along the armchair boundaries, manifesting an unusual hybridization between the edge and bulk states. Experimentally, both zigzag and armchair edge states are observed in photonic BPN lattices written in a nonlinear crystal. Furthermore, the different features of the armchair boundary are clarified between the uniform BPN and graphene lattices. These results demonstrated here may be applicable to carbon‐based BPNs and other artificial platforms beyond photonics, holding promise for expanding the application scope of 2D materials.