When phononic crystals fail: Spatial and spectral limits of phonon interference

Phononic crystals are artificial periodic structures that leverage phonon wave interference to control mechanical vibrations at various length scales. Their spatial and spectral limits, however, are currently unknown. The authors report experimental observations of a surprising breakdown of phonon interference in two-dimensional nanoscale phononic crystals. These findings refine the current understanding of nanoscale phonon interference, and should guide phononic crystal applications in microelectronics and acoustic quantum computing.