Interlayer Exciton-Phonon Bound State in BiSe/Monolayer WS van der Waals Heterostructures.

The ability to assemble layers of two-dimensional (2D) materials to form permutations of van der Waals heterostructures provides significant opportunities in materials design and synthesis. Interlayer interactions can enable desired properties and functionality, and understanding such interactions is essential to that end. Here we report formation of interlayer exciton-phonon bound states in BiSe/WS heterostructures, where the BiSe A surface phonon, a mode particularly susceptible to electron-phonon coupling, is imprinted onto the excitonic emission of the WS. The exciton-phonon bound state (or exciton-phonon quasiparticle) presents itself as evenly separated peaks superposed on the WS excitonic photoluminescence spectrum, whose periodic spacing corresponds to the A surface phonon energy. Low-temperature polarized Raman spectroscopy of BiSe reveals intense surface phonons and local symmetry breaking that allows the A surface phonon to manifest in otherwise forbidden scattering geometries. Our work advances knowledge of the complex interlayer van der Waals interactions and facilitates technologies that combine the distinctive transport and optical properties from separate materials into one device for possible spintronics, valleytronics, and quantum computing applications.