Phonon coherence and minimum thermal conductivity in disordered superlattices

Phonon coherence elucidates the propagation and interaction of phonon quantum states within superlattice, unveiling the wavelike nature and collective behaviors of phonons. Taking MoSe2/WSe2 lateral heterostructures as a model system, we demonstrate that the intricate interplay between wavelike and particlelike phonons, previously observed in perfect superlattice only, also occurs in disordered superlattice. By employing molecular dynamics simulation based on a highly accurate and efficient machine-learned potential constructed herein, we observe a nonmonotonic dependence of the lattice thermal conductivity on the interface density in both perfect and disordered superlattice, with a global minimum occurring at relatively higher interface density for disordered superlattice. The counterintuitive phonon coherence contribution can be characterized by the lagged self-similarity of the structural sequences in the disordered superlattice. Our findings extend the realm of coherent phonon transport from perfect superlattice to more general structures, which offers more flexibility in tuning thermal transport in superlattices.