Cavity-Assisted Coherent Phonon Generation and Control in a WSe₂/Au Structure

Coherent phonons in the Terahertz (THz) regime have gained attention as potential candidates for next-generation high-speed, low-energy information carriers in atomically thin phononic or phonon-integrated on-chip devices. Nevertheless, achieving efficient control of the phonon generation dynamics over THz coherent phonons continues to pose a considerable challenge. In this work, we explore THz coherent phonon generation in exfoliated van der Waals (vdW) flakes of WSe₂ on Au (WSe₂/Au) and Si (WSe₂/Si) by using time-resolved pump-probe spectroscopy. The generation of THz coherent phonons was studied as a function of the WSe₂ layer thickness and laser wavelength. Notably, a significant enhancement in THz coherent phonon generation was observed in the WSe₂/Au structure, but only within a specific range of WSe₂ thicknesses and laser wavelengths. The results from numerical simulations, which consider a self-hybridized optical cavity depending on WSe₂ thickness and optical reflectance and Raman spectroscopy measurements, all align well with the time-domain observations of THz coherent phonon generation. We propose that the observed enhancement in THz coherent phonon generation is strongly influenced by light-matter interactions in the WSe₂ cavity, a mechanism that may be applicable to a broader range of vdW materials. These findings offer promising insights for the development of THz phononic or phonon-integrated devices.