Topological insulators have a bandgap in their bulk, which means that transport can only occur through topologically protected edge states. These states are robust to disorder when it’s weak, but for sufficiently strong disorder, all the bandgaps are closed, meaning topological features should be destroyed. The prediction that non-trivial topology can emerge from a trivial band structure with the addition of disorder therefore came as something of a surprise. Now, Eric Meier and co-workers have verified the prediction by observing such a phase.

The authors demonstrated a topological Anderson insulator in atomic wires made of ultracold atoms. Their system was designed so that disorder could be added through random tunnelling, and the topological phases were identified by measuring the mean chiral displacement. When the amplitude of the random tunnelling was large enough, the authors showed that an initially clean and trivial system could be driven into a topologically non-trivial phase, in which topology manifested in the localized states of the spectrum.