Charge-Induced Second-Harmonic Generation in Bilayer WSe2

Abstract

Controlling nonlinear light-matter interaction is important from fundamental science point of view as well as a basis for future optoelectronic devices1,2. Recent advances in twodimensional crystals have created opportunities to manipulate nonlinear processes electrically3-8. Here we report a strong second-harmonic generation (SHG) in a 2D WSe2 bilayer crystal caused by a back gate field. This unusual process takes place only when the gate polarity causes charge accumulation rather than depletion. Analysis based on bondcharge model traces the origin of SHG to the non-uniform field distribution within a single monolayer, caused by the accumulated sub-monolayer screening charge in the tungsten plane. We name this phenomenon charge-induced SHG (CHISHG), which is fundamentally different from the field- or current-induced SHG3-11. Our findings provide a potentially valuable technique for understanding and noninvasive probing of charge and current distributions in future low dimensional electronic devices.