中国物理B ›› 2026, Vol. 35 ›› Issue (3): 34201-034201.doi: 10.1088/1674-1056/ae3557

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Charge-imbalance-induced second harmonic generation in twisted graphene

Ronghui Luo(罗荣辉)1, Shiyang Liu(刘诗洋)1, Xiao Dong(董校)1, Jianguo Tian(田建国)1, and Zhibo Liu(刘智波)1,2,†   

  1. 1 The Key Laboratory of Weak Light Nonlinear Photonics, Ministry of Education, School of Physics and Teda Applied Physics Institute, Nankai University, Tianjin 300071, China;
    2 The Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
  • 收稿日期:2025-12-08 修回日期:2025-12-26 接受日期:2026-01-08 发布日期:2026-02-11
  • 基金资助:
    Project supported by the National Natural Science Foundation of China (Grant Nos. 12574339, 12574457, and 12174207) and Tianjin Science and Technology Project (Grant No. 24ZXZSSS00120).

Charge-imbalance-induced second harmonic generation in twisted graphene

Ronghui Luo(罗荣辉)1, Shiyang Liu(刘诗洋)1, Xiao Dong(董校)1, Jianguo Tian(田建国)1, and Zhibo Liu(刘智波)1,2,†   

  1. 1 The Key Laboratory of Weak Light Nonlinear Photonics, Ministry of Education, School of Physics and Teda Applied Physics Institute, Nankai University, Tianjin 300071, China;
    2 The Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
  • Received:2025-12-08 Revised:2025-12-26 Accepted:2026-01-08 Published:2026-02-11
  • Contact: Zhibo Liu E-mail:liuzb@nankai.edu.cn
  • Supported by:
    Project supported by the National Natural Science Foundation of China (Grant Nos. 12574339, 12574457, and 12174207) and Tianjin Science and Technology Project (Grant No. 24ZXZSSS00120).

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摘要： Twist-and-stack engineering provides a programmable degree of freedom for nonlinear optics in two-dimensional materials, yet in a homostructure whose constituents have no second harmonic generation (SHG), how interlayer coupling grants and tunes second-order response remains unclear. Here, we use twisted monolayer-bilayer graphene ($t(1+2)$LG) and combine microscopic SHG spectroscopy with first-principles differential charge-density analysis to establish a unified ``permission-and-resonance'' mechanism. Interlayer coupling creates an interlayer charge imbalance within the AB-stacked bilayer, breaking inversion symmetry and thereby permitting an in-plane electric-dipole response. At the same time, the twist angle steers van Hove singularities in the band structure to achieve two-photon resonance, which markedly amplifies the susceptibility $\chi^{(2)}$. Experimentally, at $\theta =13.5^\circ $, we obtain $\chi^{(2)}=279.4$ pm/V, evidencing a highly efficient second-order response. These results identify SHG as a sensitive probe of interlayer coupling and charge redistribution in homostructure van der Waals systems.

关键词: second harmonic generation, charge imbalance, twisted graphene

Abstract: Twist-and-stack engineering provides a programmable degree of freedom for nonlinear optics in two-dimensional materials, yet in a homostructure whose constituents have no second harmonic generation (SHG), how interlayer coupling grants and tunes second-order response remains unclear. Here, we use twisted monolayer-bilayer graphene ($t(1+2)$LG) and combine microscopic SHG spectroscopy with first-principles differential charge-density analysis to establish a unified ``permission-and-resonance'' mechanism. Interlayer coupling creates an interlayer charge imbalance within the AB-stacked bilayer, breaking inversion symmetry and thereby permitting an in-plane electric-dipole response. At the same time, the twist angle steers van Hove singularities in the band structure to achieve two-photon resonance, which markedly amplifies the susceptibility $\chi^{(2)}$. Experimentally, at $\theta =13.5^\circ $, we obtain $\chi^{(2)}=279.4$ pm/V, evidencing a highly efficient second-order response. These results identify SHG as a sensitive probe of interlayer coupling and charge redistribution in homostructure van der Waals systems.

Key words: second harmonic generation, charge imbalance, twisted graphene

中图分类号:  (Frequency conversion; harmonic generation, including higher-order harmonic generation)

  • 42.65.Ky
78.67.-n (Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures)