title: Broken Symmetry Induced Strong Nonlinear Optical Effects in Spiral WS2Nanosheets.
abstract: Transition metal dichalcogenides (TMDs) have provided a fundamental stage to study light-matter interactions and optical applications at the atomic scale due to their ultrathin thickness and their appropriate band gap in the visible region. Here, we report the strong nonlinear optical effects, including second-harmonic generation (SHG) and third-harmonic generation (THG) in spiral WS2structures. SHG intensity quadratically increases with layer numbers, other than diminishing the oscillation of 2H stacking TMDs. The contrary SHG behavior is attributed to the broken symmetry from twisted screw structures, revealed by aberration-corrected transmission electronic microscope observation. Furthermore, the twist angle of the screw structure (5 degrees) was obtained by high-resolution transmission microscope measurements and confirmed by polarization tests of SHG output. Moreover, we roughly estimate the effective second-order nonlinear susceptibility. The discovery and understanding of the accumulation of nonlinear susceptibility of spiral structures with increasing thickness will extend the nonlinear applications of TMDs.
authors.affiliation: Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, State Key Laboratory of Chemo/Biosensing and Chemometrics, and School of Physics and Electronics, Hunan University , Changsha 410082, People's Republic of China.
authors.forename: Xiaopeng
authors.initials: X
authors.lastname: Fan
authors.affiliation: Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, State Key Laboratory of Chemo/Biosensing and Chemometrics, and School of Physics and Electronics, Hunan University , Changsha 410082, People's Republic of China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Jiang
authors.affiliation: Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, State Key Laboratory of Chemo/Biosensing and Chemometrics, and School of Physics and Electronics, Hunan University , Changsha 410082, People's Republic of China.
authors.forename: Xiujuan
authors.initials: X
authors.lastname: Zhuang
authors.affiliation: Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, State Key Laboratory of Chemo/Biosensing and Chemometrics, and School of Physics and Electronics, Hunan University , Changsha 410082, People's Republic of China.
authors.forename: Hongjun
authors.initials: H
authors.lastname: Liu
authors.affiliation: SEU-FEI Nano-Pico Center, Key Lab of MEMS of Ministry of Education, Southeast University , Nanjing 210096, People's Republic of China.
authors.forename: Tao
authors.identifier: 0000-0001-5436-0077
authors.initials: T
authors.lastname: Xu
authors.affiliation: Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, State Key Laboratory of Chemo/Biosensing and Chemometrics, and School of Physics and Electronics, Hunan University , Changsha 410082, People's Republic of China.
authors.forename: Weihao
authors.initials: W
authors.lastname: Zheng
authors.affiliation: Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, State Key Laboratory of Chemo/Biosensing and Chemometrics, and School of Physics and Electronics, Hunan University , Changsha 410082, People's Republic of China.
authors.forename: Peng
authors.initials: P
authors.lastname: Fan
authors.affiliation: Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, State Key Laboratory of Chemo/Biosensing and Chemometrics, and School of Physics and Electronics, Hunan University , Changsha 410082, People's Republic of China.
authors.forename: Honglai
authors.identifier: 0000-0002-4321-1807
authors.initials: H
authors.lastname: Li
authors.affiliation: Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, State Key Laboratory of Chemo/Biosensing and Chemometrics, and School of Physics and Electronics, Hunan University , Changsha 410082, People's Republic of China.
authors.forename: Xueping
authors.initials: X
authors.lastname: Wu
authors.affiliation: Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, State Key Laboratory of Chemo/Biosensing and Chemometrics, and School of Physics and Electronics, Hunan University , Changsha 410082, People's Republic of China.
authors.forename: Xiaoli
authors.initials: X
authors.lastname: Zhu
authors.affiliation: Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, State Key Laboratory of Chemo/Biosensing and Chemometrics, and School of Physics and Electronics, Hunan University , Changsha 410082, People's Republic of China.
authors.forename: Qinglin
authors.initials: Q
authors.lastname: Zhang
authors.affiliation: Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, State Key Laboratory of Chemo/Biosensing and Chemometrics, and School of Physics and Electronics, Hunan University , Changsha 410082, People's Republic of China.
authors.forename: Hong
authors.initials: H
authors.lastname: Zhou
authors.affiliation: Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, State Key Laboratory of Chemo/Biosensing and Chemometrics, and School of Physics and Electronics, Hunan University , Changsha 410082, People's Republic of China.
authors.forename: Wei
authors.initials: W
authors.lastname: Hu
authors.affiliation: Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, State Key Laboratory of Chemo/Biosensing and Chemometrics, and School of Physics and Electronics, Hunan University , Changsha 410082, People's Republic of China.
authors.forename: Xiao
authors.initials: X
authors.lastname: Wang
authors.affiliation: SEU-FEI Nano-Pico Center, Key Lab of MEMS of Ministry of Education, Southeast University , Nanjing 210096, People's Republic of China.
authors.forename: Litao
authors.initials: L
authors.lastname: Sun
authors.affiliation: Department of Materials Science and Engineering, Department of Chemistry and Biochemistry, and California NanoSystems Institute, University of California , Los Angeles, California 90095, United States.
authors.forename: Xiangfeng
authors.identifier: 0000-0002-4321-6288
authors.initials: X
authors.lastname: Duan
authors.affiliation: Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, State Key Laboratory of Chemo/Biosensing and Chemometrics, and School of Physics and Electronics, Hunan University , Changsha 410082, People's Republic of China.
authors.forename: Anlian
authors.identifier: 0000-0003-3335-3067
authors.initials: A
authors.lastname: Pan
keywords: nonlinear optics; polarization; second-harmonic generation (SHG); spiral structure; third-harmonic generation (THG); tungsten disulfide