Two-Dimensional Pyramid-like WS2 Layered Structures for Highly Efficient Edge Second-Harmonic Generation.

Two-dimensional (2D) layered materials, with large second-order nonlinear susceptibility, have received much scientific interest due to their potential applications in nonlinear optical devices. However, the atomic thickness of 2D layered materials leads to poor field confinement and weak light-matter interaction at the nanoscale, resulting in low nonlinear conversion efficiency. Here, 2D pyramid-like multilayer (P-multilayer) layered structures are fabricated for efficient edge second-harmonic generation (SHG) based on the enhanced light-matter interaction in whispering-gallery mode (WGM) cavities. The P-multilayer 2D layered materials, where the basal planes shrink gradually from the bottom to the top layers, exhibit efficient edge SH radiation due to the partial destructive interference of nonlinear polarizations between the neighboring atomic layers. Moreover, the well-defined 2D plate-like triangle morphology of P-multilayer WS2 forms a WGM resonance cavity, which results in enhanced light-matter interaction and thus the enhancement of edge SHG, which can be further enhanced by hybridizing the WGM mode with plasmonics. These results provide enlightenment for the construction of specific structures for efficient nonlinear processes.