title: Charge-Induced Second-Harmonic Generation in Bilayer WSe2.
abstract: Controlling nonlinear light-matter interaction is important from a fundamental science point of view as well as a basis for future optoelectronic devices. Recent advances in two-dimensional crystals have created opportunities to manipulate nonlinear processes electrically. 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 a bond-charge model traces the origin of SHG to the nonuniform field distribution within a single monolayer, caused by the accumulated submonolayer screening charge in the tungsten plane. We name this phenomenon charge-induced SHG (CHISHG), which is fundamentally different from the field- or current-induced SHG. Our findings provide a potentially valuable technique for understanding and noninvasive probing of charge and current distributions in future low dimensional electronic devices.
authors.affiliation: †Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 637371 Singapore.
authors.forename: Huakang
authors.initials: H
authors.lastname: Yu
authors.affiliation: †Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 637371 Singapore.
authors.forename: Deep
authors.initials: D
authors.lastname: Talukdar
authors.affiliation: †Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 637371 Singapore.
authors.forename: Weigao
authors.initials: W
authors.lastname: Xu
authors.affiliation: ‡Department of Electrical and Computer Engineering, Johns Hopkins University, Baltimore, Maryland 21218, United States.
authors.forename: Jacob B
authors.initials: JB
authors.lastname: Khurgin
authors.affiliation: †Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 637371 Singapore.|§NOVITAS, Nanoelectronics Centre of Excellence, School of Electrical and Electronic Engineering, Nanyang Technological University, 639798 Singapore.
authors.forename: Qihua
authors.initials: Q
authors.lastname: Xiong
keywords: Charged-induced second-harmonic generation; bond charge model; charge accumulation; screening effect; tungsten diselenide; two-dimensional layered materials