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.
SHG polar plots of MnPSe3/graphene heterojunction (a) and MnPSe3 layer alone (b). (Image by LI Bolin)
