Direct observation of Klein tunneling in phononic crystals

A sound demonstration of Klein tunneling The ability of particles to tunnel through barriers is an important property of quantum mechanical systems, and the extent of the effect is strongly dependent on the properties of the barrier. By contrast, Klein tunneling can exhibit unity transmission that is independent of the width and height of the energy barrier, but direct evidence for this effect remains elusive. Using a phononic system comprising a periodic array of dielectric pillars, Jiang et al. provide evidence for the direct observation of Klein tunneling. Near-unity transmission of acoustic excitations was observed across the barrier independently of its width and height. This ability to tune the effect by controlling the size of the junctions and the frequency of incident waves provides a promising platform to explore complex nontrivial physics and applications in signal processing and information communications. Science , this issue p. 1447