Among the crystalline materials whose edges host exotic quantum states are the Dirac semimetal and the Chern insulator. In the semimetal, the edge states are localized and not protected from perturbations by their topology; in the insulator, they move in one direction and are protected. Proposed by theorists in 2011, a hybrid phase called a Chern semimetal simultaneously hosts localized and one-way edge states, both with topological protection (see Synopsis: Quantum Hall Anomaly in 3D). Now Jianfeng Chen and Cheng-Wei Qiu at the National University of Singapore and their colleagues have realized this phase in a two-dimensional photonic metamaterial [1]. The researchers say that their system provides a platform for nanophotonic applications and a playground for topological physics.
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