All-angle acoustic topological insulators: from omnidirectional antennas to angle-tunable Klein tunneling.

Conventional Dirac cones are tightly pinned at high-symmetry points in reciprocal space, although they can be slightly shifted through straining or stretching. In this work, we discuss an approach to translate Dirac cones across the entire Brillouin zone of a 2D topological sonic metamaterial that is based upon a tilted Su-Schrieffer-Heeger model. By judiciously engineering the associated hopping amplitudes, one can readily alter the positions of the Dirac cones, thereby broadening the possibilities for a wide range of applications and phenomena. For example, we present an experimental demonstration of out-coupled nontrivial edge states, capable of radiating in any direction. Additionally, we use this approach to demonstrate Klein tunneling effects that can be achieved at arbitrary angles of incidence. We anticipate that our findings will expand the prospect of both fundamental and applied topological physics.