Accurately Controlling Angle-Resolved Second Harmonic Generation by Stacking Orders from a MoS2 Homobilayer

As an efficient way to control crystal symmetry, the stacking order introduces a degree of freedom of twist angle, offering a powerful platform to engineer artificial vertically stacked van der Waals (vdW) structures for nonlinear twistoptics. Herein, we show that stacking orders of a MoS2 homobilayer results in strong tunability of interlayer coupling and second harmonic generation (SHG). The interlayer coupling exhibits a strong dependence on the alignment and staggering degree of the sulfur atoms in the two MoS2 layers. Controlling the in-plane and out-of-plane charge density symmetry by the stacking order can adjust the number and dispersion of second-order nonlinear coefficients in a MoS2 homobilayer. Besides, the angle-resolved SHG pattern of the MoS2 homobilayer with different stacking orders can be distinguished only under oblique incidence, which solves the experimental difficulty in distinguishing the SHG pattern of similar homobilayers such as 3R and 3R-like bilayers. Our results pave the way for the stacking engineering to tune the nonlinear optical response and the angle-dependent SHG pattern to probe the symmetry of stacked vdW structures.