Acoustic spin-dependent topological bound states in the continuum with antihelical transport
Phys. Rev. B 113, 075307 – Published 17 February, 2026
DOI: https://doi.org/10.1103/gmbp-csmg
Abstract
Bound states in the continuum (BICs) are spatially confined modes that coexist within the continuous spectrum propagating in the medium. The combination with topological physics gives rise to the topological BICs, which inherit the characteristics of traditional BICs and also have the features of topological protection. Here, we report the spin-dependent topological BICs that can support antihelical edge transport modes in a phononic crystal. We employ two decoupled spin subspaces as a bridge to topological BICs, which not only enable the spin-dependent topological BICs but also exhibit novel transport properties, antihelical edge transport. We experimentally realize the spin-dependent topological BICs in a phononic crystal and observe their hallmark, antihelical edge states embedded in the bulk structure with opposite spin. Furthermore, by tuning the interlayer coupling strengths, we experimentally achieve the independent modulation of the two topological BICs with different spins, giving rise to a hybrid system where spin-dependent topological BICs and topological flat bands coexist. Our work deepens the understanding of constructing topological BICs via spin subspaces and opens new avenues for hybrid multimode transport.
