Observation of boundary induced chiral anomaly bulk states and their transport properties

TL;DR

This paper demonstrates that boundary conditions in a topologically trivial 2D phononic crystal can induce chiral anomaly bulk states with robust valley-selected transport, revealing a novel boundary-driven topological phenomenon.

Contribution

It shows that boundary-induced effects can generate chiral anomaly bulk states in trivial topological systems, reversing the usual bulk-to-boundary influence in topological materials.

Findings

Observed robust valley-selected transport in phononic waveguides

Demonstrated complete valley state conversion and focusing of chiral anomaly bulk states

Validated the existence of boundary-induced chiral anomaly bulk states

Abstract

The robust transport of edge modes is perhaps the most useful property of topological materials. The existence of edge modes is guaranteed by the bulk-edge correspondence, which states that the number of topological edge modes is determined by the bulk topological invariants. To obtain robust transport on the edge, we need to make volumetric changes to many bulk atoms to control the properties of a few edge atoms in a lower dimension. We suggest here that we can do the reverse in some cases: the properties of the edge can guarantee chiral transport phenomena in some bulk modes, achieving phenomena that are essentially the same as those observed in topological valley-Hall systems. Specifically, we show that a topologically trivial 2D hexagonal phononic crystal slab (waveguide) bounded by hardwall boundaries guarantees the existence of bulk modes with chiral anomaly inside a pseudogap. We experimentally observed robust valley-selected transport, complete valley state conversion, and valley focusing of the chiral anomaly bulk states (CABSs) in such phononic crystal waveguides.