A research group led by Prof. SHENG Zhigao from the Hefei Institutes of Physical Science of the Chinese Academy of Sciences , recently discovered the disappearance of nonreciprocal second harmonic generation (SHG) in MnPSe₃ when integrated into a two-dimensional (2D) antiferromagnetic MnPSe₃/graphene heterojunction.
The research, published in Nano Letters, highlights the role of interfacial magnon-plasmon coupling in this phenomenon.
2D van der Waals magnetic/non-magnetic heterojunctions hold significant promise for spintronic devices. Achieving these functionalities hinges on the interfacial proximity effect, a critical factor. However, detecting the proximity effect in 2D antiferromagnetic/non-magnetic heterojunctions presents considerable challenges, due to the small size and weak signals associated with these structures.
In this study, the team used a home-made SHG system to observe that the nonreciprocal SHG of MnPSe₃ disappeared when it was in contact with graphene, in contrast to the antiferromagnetic MnPSe₃ layer alone. This change indicates the presence of interfacial coupling interaction or proximity effect.
To explore this effect further, the researchers incorporated a hexagonal boron nitride (h-BN) layer between the MnPSe₃ and graphene to isolate the interfacial interaction. Their experiments revealed that the interfacial coupling extended over a long range (>40 nm), significantly surpassing the typical range of a few nanometers typically observed in proximity effects.
Moreover, the team found that the strength of this coupling weakened as the band gap of the underlayer material increased, providing a way to tune the nonlinear SHG response. Through symmetry analysis, first-principles calculations, and comparison with previous studies, the researchers concluded that the disappearance of the nonreciprocal SHG signal was due to the coupling between graphene' s surface plasmons and MnPSe₃' s magnons.
"This discovery paves the way for manipulating the nonlinear optical properties of 2D heterojunctions and developing multifunctional, tunable 2D layered nonlinear optical devices," said Prof. SHENG Zhigao.
