Abstract
Phononic crystals are artificial periodic structures that leverage phonon-wave interference to control mechanical vibrations. Their practical implementations range from evenly planted trees to periodic nanostructures covering mechanical vibrations from seismic waves to sound and heat. However, the spatial and spectral limits at which phonon interference disappears are unknown. Here, we report on experimental observations of a gradual breakdown of phonon interference in two-dimensional nanoscale phononic crystals. Measured phonon dispersion relations reveal the critical dimensions and frequencies at which phonons no longer sense the in-plane periodicity of the crystal and enter an intermediate state dominated by out-of-plane interference before ceasing to interfere altogether. These findings refine the current understanding of nanoscale phonon interference and might be relevant for phononic crystal applications in microelectronics and acoustic quantum computing.
Physical Review Applied 24, L061001 (2025)