Nonlinear Optical Response in Natural van der Waals Heterostructures

Abstract Van der Waals heterostructures (vdWH) composed from individual 2D crystals offer a platform to obtain unprecedented functionalities that are not accessible in other heterostructures. The research to date has been largely limited to exfoliated and restacked flakes, and the controlled growth of such heterostructures remains a significant challenge. Here, an experimental study of the broadband nonlinear optical performance of a naturally occurring vdWH franckeite is presented, which is composed of alternating SnS₂‐like and PbS‐like layers stacked on top of each other. Few‐layer franckeite is prepared via liquid‐phase exfoliation method and its broadband ultrafast third‐order nonlinear optical behavior is characterized experimentally. It is found that the layered franckeite exhibits broadband nonlinear optical response and the ultrafast carrier dynamics with the intraband carrier recovery time of ≈16 ps and the interband carrier recovery time of ≈300 ps. With the large optical nonlinearity of layered franckeite, the all‐optical modulator and switcher have been demonstrated based on the spatial phase modulation effect. The experimental results provide a fundamental understanding of the ultrafast nonlinear optical response in a complex naturally occurring vdWH, and may pave an avenue toward developing novel broadband optoelectronic devices.