Spin-chirality-driven second-harmonic generation in two-dimensional magnet CrSBr.

The interplay between magnetism and light can create abundant optical phenomena. Here, we demonstrate the emergence of an unconventional magnetization-induced second-harmonic generation (MSHG) stemming from vector spin chirality, denoted as chiral second-harmonic generation (SHG). Taking the antiferromagnetic (AFM) CrSBr bilayer as a prototype, we theoretically show that, via spin canting, the chiral SHG can be continuously tuned from zero to a value one order of magnitude larger than its intrinsic MSHG. Chiral SHG is found to be proportional to spin chirality and spin-canting-induced electric polarization, while intrinsic MSHG is proportional to the Néel vector, demonstrating their different physical mechanisms. Additionally, we reveal a unique interference effect between these two types of MSHG under the reversal of spin-canting direction, generating a giant modulation of SHG signals. Our work not only uncovers a unique SHG with exceptional tunability but also promotes the applications of AFM optical devices and magnetoelectric detection techniques.