Immunity to Backscattering of Bulk Waves in Topological Acoustic Superlattices

We herein investigate the scattering of orthogonal counterpropagating waves and one-way propagating bulk waves in discrete acoustic superlattices subjected to a scattering potential applied to one of the superlattice unit cells. We demonstrate theoretically that the orthogonality of counterpropagating modes does not provide robust protection against backscattering. By contrast, the one-way propagating modes do satisfy a no-reflection condition, i.e., they exhibit immunity to backscattering, for a wide range of applied scattering potentials, which represent defects and disorder.