Dynamics, hybridization, and thermalization of phonons in optically excited twisted TMD bilayers

One primary limitation to implementing van-der-Waals (vdW) stacked materials in future nanodevices is the management of heat between layers. Recent experiments and calculations show that heterostructures of transition metal dichalcogenide (TMD) bilayers are surprisingly inefficient heat conductors. They display a thermal boundary conductivity across layers as small as 1.4 W m^-1K^-1 – comparable to the thermal resistance of 300 nm of glass. This is particularly relevant to the dynamics of excitons in TMD bilayers, which are typically initialized optically first as an intralayer exciton, but quickly relax within ~50 fs into a spatially separated interlayer exciton, releasing phonons with a non-thermal distribution. Here, we evaluate the role of individual phonons and interfacial twist angle in the interlayer heat transfer. We focus on initial phonons created by the relaxation of intralayer excitons in twisted TMD bilayers and explore the mode- and time-resolved phonon dynamics, including phonon-phonon interactions, from first-principles-parametrized atomistic calculations. These methods give insight into the effects of atomic relaxation and the formation of strain solitons in these large-scale moiré TMDs, elucidating how one might engineer more efficient interlayer heat transfer.