Pressuring-tuning of moiré phonons in MoS₂/WSe₂ heterostructures

Moiré superlattices can be created by stacking two-dimensional crystals with a small lattice mismatch or twist-angle between the layers. The associated moiré potential can give rise to new excitations in the system, such as moiré phonons: phonons from the individual layers downfolded to zone center through the periodicity of the moiré potential. Hydrostatic pressure can be a powerful tool to study and further tune those excitations. Here, we investigate the evolution of moiré phonons in a rotationally-aligned MoS₂/WSe₂ moiré heterostructure at high-pressures via Raman spectroscopy. Moiré phonons are revealed as satellite Raman peaks that appear exclusively in the heterostructure region, which are found to blueshift and increase in intensity under the application of pressure. By combining density functional theory and an effective model of the pressure-dependent moiré potential with zone folding analysis, we are able to assign the satellite peaks to downfolded MoS₂ optical phonons and accurately capture their evolution with pressure. Our theoretical analysis further illustrates the microscopic process that generates moiré phonons which can be associated to an electron-phonon scattering process within the mini-Brillouin zone. Crucially, this connection to the electronic system establishes moiré phonons as a sensitive probe of the mini-band electronic structure in moiré systems. Our work may shed light on the interplay between moiré potentials, phonons and electron-phonon scattering in novel moiré systems.