Incoherent phonon transport dominates heat conduction across van der Waals superlattices

Heat conduction mechanisms in superlattices could be different across different types of interfaces. Van der Waals superlattices are structures physically assembled through weak van der Waals interactions by design and may host properties beyond the traditional superlattices limited by lattice matching and processing compatibility, offering a different type of interface. In this work, natural van der Waals (SnS)1.17(NbS2)n superlattices are synthesized, and their thermal conductivities are measured by time-domain thermoreflectance as a function of interface density. Our results show that heat conduction of (SnS)1.17(NbS2)n superlattices is dominated by interface scattering when the coherent length of phonons is larger than the superlattice period, indicating that incoherent phonon transport dominates through-plane heat conduction in van der Waals superlattices even when the period is atomically thin and abrupt, in contrast to conventional superlattices. Our findings provide valuable insights into the understanding of the thermal behavior of van der Waals superlattices and devise approaches for effective thermal management of superlattices depending on the distinct types of interfaces.