Spectral picture of thermal phonon Anderson localization in binary superlattices

In the emerging field of phononics, wave effects such as Anderson localization are expected to provide essential insight for quenching of heat transport in, e.g., thermoelectric applications. However, the currently limited understanding of Anderson localization in phononic systems leaves its prospect for potential practical applicability in heat management an open question. Our atomistic study on disordered binary superlattices provides a systematic avenue for exploiting phononic wave localization, achieving an ultralow thermal conductivity and an anomalously large thermal anisotropy in realistic semiconductor systems at ambient conditions. We provide a detailed spectrally decomposed description on the interrelationship between wave interference, anharmonicity, and incoherent impurity scattering. Finally, fundamental insight on the origin of phononic localization is elucidated through harmonic analysis.