Let Disorder Dictate Topology

One of the boons of topological insulators is that their conducting edge states are protected from disorder in the material’s structure. Turn up the disorder too much, however, and these topological features are usually lost. In 2018, experiments demonstrated the opposite behavior: in so-called topological Anderson insulators (TAIs), the addition of disorder can generate protected edge states, turning a trivial insulator into a topological one. Now, a team led by Baile Zhang of Nanyang Technological University in Singapore reports a new type of TAI realized in a photonic crystal [1]. Their experiments show that the crystal exhibits a wealth of topological phenomena that hadn’t been seen previously.