Prominent phonon transmission across aperiodic superlattice through coherent mode-conversion

In both particle and wave descriptions of phonons, the dense, aperiodically arranged interfaces in aperiodic superlattices are expected to strongly attenuate thermal transport due to phonon-interface scattering or broken long-range coherence. However, considerable thermal conductivity is still observed in these structures. In this study, we reveal that incoherent modes propagating in the aperiodic superlattice can convert, through interference, into coherent modes defined by an approximate dispersion relation. This conversion leads to high transmission across the aperiodic superlattice structure, which contains hundreds of interfaces, ultimately resulting in significant thermal conductivity. Such incoherent-to-coherent mode conversion behavior is extensively observed in periodic superlattices. This work suggests an effective strategy to manipulate the phonon band structure through layer patterning or material choice, enabling precise control of phonon transmission across aperiodic superlattices.