Observation of anomalous Floquet non-Abelian topological insulators

Abstract: Non-Abelian topological phases, which go beyond traditional Abelian topological band theory, are garnering increasing attention. This is further spurred by periodic driving, leading to predictions of many novel multi-gap Floquet topological phases, including anomalous Euler and Dirac string phases induced by non-Abelian Floquet braiding, as well as Floquet non-Abelian topological insulators (FNTIs) that exhibit multifold bulk-edge correspondence. Here, we report the first experimental realization of anomalous FNTIs, which demonstrate topological edge modes in all three gaps despite having a trivial bulk charge. Concretely, we construct an experimentally feasible one-dimensional three-band Floquet model and implement it in acoustics by integrating time-periodic coupling circuits to static acoustic crystals. Furthermore, we observe counterintuitive topological interface modes in the domain-wall formed by an anomalous FNTI and its counterpart with swapped driving sequences, modes previously inaccessible in Floquet Abelian systems. Our work paves the way for further experimental exploration of the uncharted non-equilibrium topological physics.