Edge-Oriented Surface Plasmons and Out-of-Plane Phonon-Coupling-Manipulated Davydov Splitting in WS₂ Flakes with Nonexciton Resonance Excitation under Ambient Conditions

Two-dimensional (2D) materials with van der Waals (vdW) interactions have driven significant advancements in electronics, optics, and materials science. Controlling and understanding interlayer interactions are crucial to expanding their potential applications. Davydov splitting, which is associated with phonon-electron-exciton-coupling dynamics, offers a method to investigate and assess interlayer interactions in 2D vdW materials. Here we report a significant Davydov splitting of the out-of-plane (OP) mode observed in 10-nm-thick WS₂ flakes placed at the edge of gold thin films under ambient conditions. The Raman intensity of the OP mode increased over 1000-fold due to the coupling between OP phonons and edge-oriented plasmons, accompanied by a splitting peak controllable via polarized incident light and surface plasmons. The plasmon-phonon-coupling-induced splitting under nonexciton resonance excitation offers a new approach to controlling interlayer coupling in multilayer 2D materials, unlocking further opportunities for manipulating quantum phenomena in vdW homostructures and heterostructures.