The efficiency of nonlinear optical processes in 2D materials is often reduced by weak light-matter interactions and crystal symmetry constraints. Here, the authors report the enhancement of classical second-harmonic generation in hexagonal boron nitride and quantum spontaneous parametric down-conversion in NbOCl2 flakes by combining them with Au or SiO2/Au substrates.
- Xiaodan Lyu
- Leevi Kallioniemi
- Weibo Gao
