Surface acoustic waves-driven magnon spin Hall effect in atomically thin van der Waals antiferromagnets

Intrinsic 2D magnetism had long been believed to hardly survive due to the enhanced thermal fluctuations. However, the recent discovery of exfoliated van der Waals (vdW) magnets has opened up a new avenue for 2D magnetism. Especially, transition metal phosphorus trichalcogenides are a family of easily exfoliatable vdW antiferromagnets. These materials share the same honeycomb structure, but the bulk antiferromagnetic (AFM) phase varies depending on the magnetic elements. Therefore, the investigation of these materials paves the way toward not only the understanding of 2D magnetism, but also future AFM spintronic devices.

However, standard methods are not suitable for the study of atomically thin magnets. Especially, antiferromagnets do not have net magnetization, magneto-optical Kerr effect is not available either. Although recent studies have focused on Raman spectroscopy and second-harmonic generation to detect crystal symmetry lowering associated with the AFM transition, these signals do not provide clear identification in the monolayer limit. Therefore, an inclusive method which suits for exploring 2D antiferromagnets is highly desired.

By focusing on extremely large flexibility of 2D materials, we propose an intrinsic magnon spin Hall current driven by the surface-acoustic waves as a novel probe for such 2D vdW antiferromagnets. Furthermore, our results will overcome the difficulties inherent in the use of antiferromagnets and hence provide a building block for future AFM spintronics.