Investigate 2D antiferromagnetism in van der Waals materials by nonlinear optics

Detecting the spin structures in antiferromagnetic materials is normally considered hard, especially for two-dimensional materials where samples are usually thin and small. Here, I will show that the optical second-harmonic generation (SHG) is an ideal tool for detecting various types of two-dimensional antiferromagnetism, including the non-centrosymmetric Neel type and centrosymmetric Zigzag type. The polarization-dependent measurement reveals the orientations of spins and an SHG confocal microscope further generates the spin orientation distribution across the sample in the diffraction limit. I will show how we use SHG to investigate three different 2D antiferromagnets, the Heisenberg-type MnPS3, the XY-type MnPSe3, and the Ising-type FePS3.