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Published on: July 12, 2017
Giant and Actively Tunable Second-Harmonic Generation in Bilayer Graphene
Mingwen Zhang1, Yi Zhang1, Haoyu Wang2
1Key Laboratory of Light Field Manipulation and Information Acquisition, Ministry of Industry and Information Technology, and Shaanxi Key Laboratory of Optical Information Technology, School of Physical Science and Technology, Northwestern Polytechnical University, Xi'an 710129, China.
Scientists unlocked tunable second-harmonic generation in bilayer graphene by breaking its inversion symmetry with an electric field. This breakthrough enables new possibilities for nonlinear optics and integrated photonics using 2D materials.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Optoelectronics
Background:
- Graphene's centrosymmetric lattice suppresses second-order nonlinear optical responses like second-harmonic generation (SHG).
- Tuning material symmetry is key to overcoming intrinsic limitations in 2D materials.
Purpose of the Study:
- To break the inversion symmetry of bilayer graphene and activate its nonlinear optical properties.
- To demonstrate a tunable and enhanced second-harmonic generation (SHG) response.
Main Methods:
- Utilized an ion-gel top gate to apply an out-of-plane electric field, breaking bilayer graphene's inversion symmetry.
- Measured the nonlinear susceptibility (χ(2)) and performed polarization-resolved and thickness-dependent studies.
Main Results:
- Achieved a giant, actively tunable SHG response with χ(2) ∼ 300 pm/V in the communication band, significantly exceeding that of MoS2.
- Confirmed symmetry reduction to C3v point group via polarization-resolved measurements.
- Established a generalized framework for nonlinear optics in centrosymmetric 2D material stacks.
Conclusions:
- Electrostatic control of symmetry is a viable strategy for activating and tuning nonlinear optical responses in 2D materials.
- This approach opens avenues for actively tunable integrated photonics and quantum light sources.
