Journal Article

Giant nonreciprocal second-harmonic generation from antiferromagnetic bilayer CrI3

Sun, Zeyuan, Clark, Genevieve, Gao, Chunlei, Chen, Zhanghai, Wu, Shuang, Yao, Wang, Xiao, Di, Yi, Yangfan, Song, Tiancheng, Huang, Bevin, Shan, Yuwei, Huang, Di, Liu, Wei-Tao, Cao, Ting, Wu, Shiwei, McGuire, Michael, Xu, Xiaodong

2019

Overview

Layered antiferromagnetism is the spatial arrangement of ferromagnetic layers with antiferromagnetic interlayer coupling. The van der Waals magnet chromium triiodide (CrI 3 ) has been shown to be a layered antiferromagnetic insulator in its few-layer form 1 , opening up opportunities for various functionalities 2 – 7 in electronic and optical devices. Here we report an emergent nonreciprocal second-order nonlinear optical effect in bilayer CrI 3 . The observed second-harmonic generation (SHG; a nonlinear optical process that converts two photons of the same frequency into one photon of twice the fundamental frequency) is several orders of magnitude larger than known magnetization-induced SHG 8 – 11 and comparable to the SHG of the best (in terms of nonlinear susceptibility) two-dimensional nonlinear optical materials studied so far 12 , 13 (for example, molybdenum disulfide). We show that although the parent lattice of bilayer CrI 3 is centrosymmetric, and thus does not contribute to the SHG signal, the observed giant nonreciprocal SHG originates only from the layered antiferromagnetic order, which breaks both the spatial-inversion symmetry and the time-reversal symmetry. Furthermore, polarization-resolved measurements reveal underlying C 2 h crystallographic symmetry—and thus monoclinic stacking order—in bilayer CrI 3 , providing key structural information for the microscopic origin of layered antiferromagnetism 14 – 18 . Our results indicate that SHG is a highly sensitive probe of subtle magnetic orders and open up possibilities for the use of two-dimensional magnets in nonlinear and nonreciprocal optical devices. Large second-harmonic generation is observed in antiferromagnetic bilayers of CrI 3 , providing information about the microscopic origin of layered antiferromagnetism and motivating the use of two-dimensional magnets in nonlinear optical devices.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 140/125 / 639/301/357/1018 / 639/766/119/997 / 639/766/400/385 / Antiferromagnetism / Chromium / Crystal structure / Crystallography / Electronic devices / Ferromagnetism / Humanities and Social Sciences / Interlayers / Letter / Magnetic fields / Magnetic permeability / magnetic properties and materials / Magnetism / Magnets / MATERIALS SCIENCE / Molybdenum / Molybdenum disulfide / multidisciplinary / nonlinear optics / Optical materials / Optics / Photons / Resonant frequencies / Science / Science (multidisciplinary) / Second harmonic generation / Spectrum analysis / Symmetry / two-dimensional materials