Observation of coherently modulated thermal phonon band and lifetime in superlattice
Manipulating phonon band structures through wave interference in artificial periodic nanostructures is of fundamental interest and forms the foundation of phonon band engineering. Yet, direct observation of thermal phonon wave interference has remained elusive despite half a century of extensive research. Here, utilizing inelastic x-ray scattering, we directly observed momentum-resolved coherently modulated thermal phonon bands and lifetimes in a short-period GaAs/AlAs superlattice at 300 K. The modulation persists at even 500 K, demonstrating robust coherent thermal phonon transport at high temperatures. Our measurements, combined with ab initio lattice-dynamics calculations, further show that thermal phonon interference expands the three-phonon scattering phase space and strengthens anharmonic effects, highlighting the interplay between phonon band modulation and anharmonicity. Our observations establish nanostructuring as a versatile route for engineering thermal phonon bands and lifetimes at high temperatures across diverse applications.