Observation of giant surface second harmonic generation coupled to nematic orders in the van der Waals antiferromagnet FePS$_3$

TL;DR

This study reveals giant surface second harmonic generation in few-layer FePS3 below the Ne9el temperature, coupled to nematic magnetic orders, providing a new tool for probing antiferromagnetic states in centrosymmetric 2D materials.

Contribution

It demonstrates a giant surface second-harmonic generation in centrosymmetric FePS3 linked to nematic magnetic orders, expanding the understanding of nonlinear optical responses in 2D antiferromagnets.

Findings

Surface SHG in FePS3 is two orders of magnitude larger than in other magnetic systems.

SHG signal is coupled to nematic orders formed by antiferromagnetic domains.

Surface nonlinear susceptibility reaches 0.08--0.13 nm$^2$/V in 2-5 layer samples.

Abstract

Second harmonic generation has been applied to study lattice, electronic and magnetic proprieties in atomically thin materials. However, inversion symmetry breaking is usually required for the materials to generate a large signal. In this work, we report a giant second-harmonic generation that arises below the N\'eel temperature in few-layer centrosymmetric FePS$_3$. Layer-dependent study indicates the detected signal is from the second-order nonlinearity of the surface. The magnetism-induced surface second-harmonic response is two orders of magnitude larger than those reported in other magnetic systems, with the surface nonlinear susceptibility reaching 0.08--0.13 nm$^2$/V in 2 L--5 L samples. By combing linear dichroism and second harmonic generation experiments, we further confirm the giant second-harmonic generation is coupled to nematic orders formed by the three possible Zigzag antiferromagnetic domains. Our study shows that the surface second-harmonic generation is also a sensitive tool to study antiferromagnetic states in centrosymmetric atomically thin materials.