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Analogies between electronic condensed matter systems and optics attract widespread attention nowadays, underlying much research in photonics. Prominent examples where such analogies have been fruitfully developed include photonic crystals, 1 random lasers, 2 and photonic topological insulators. 3 In this Perspective, we would like to introduce and flatter a new member of this growing family: photonic flatbands.

Flatband lattices—periodic media with at least one completely dispersionless Bloch band—have been known since the 1980s, 4–7 but at the time many dismissed them as either pathological (requiring an intricate lattice design and being unstable against perturbations) or trivial (within an ideal flatband, all states are degenerate, so there are no dynamics). Indeed, the most obvious way to create a flatband is to take the Hamiltonian of any periodic system, compute its band structure, and divide it by the …