Experimental observation of non-Abelian topological acoustic semimetals and their phase transitions
Recent experiments verify prediction of studies in our group of the past year
Metamaterial realisations of non-Abelian semimetals. Various stages of the band structure show the braiding process that underpins their origin.
In a recent Nature Physics publication we verified non-Abelian semimetals studied in our group the past year. Topological phases of matter lie at the heart of physics, connecting elegant mathematical principles to real materials that are believed to shape future electronic and quantum computing technologies. To date, studies in this discipline have almost exclusively been restricted to single-gap band topology because of the Fermi-Dirac filling effect. Here, we theoretically analyze and experimentally confirm a novel class of multi-gap topological phases, the non-Abelian topological semimetals. These unprecedented forms of matter depend on the notion of Euler class and frame charges which arise due to non-Abelian charge conversion processes when band nodes of different gaps are braided along each other in momentum space. We identify such exotic phenomena in acoustic metamaterials on a kagome geometry which exhibit a rich topological phase diagram induced by the creation, braiding and recombination of band nodes. Using acoustic pump-probe measurements, we verify the non-Abelian charge conversion processes where topological charges of nodes are transferred from one gap to another. Moreover, in such processes, we discover symmetry-enforced intermediate phases featuring triply-degenerate band nodes with unique dispersions that are directly linked to the multi-gap topological invariants. Furthermore, we confirm that edge states can faithfully characterize the multi-gap topological phase diagram. Our study unveils a new regime of topological phases where multi-gap topology and non-Abelian charges of band nodes play a crucial role in understanding semimetals with inter-connected multiple bands.Experimental observation of non-Abelian topological acoustic semimetals and their phase transitions Bin Jiang, Adrien Bouhon, Zhi-Kang Lin, Xiaoxi Zhou, Bo Hou, Feng Li, Robert-Jan Slager, Jian-Hua Jiang, Nature Physics (2021).