Multiple van Hove Singularities and Layer-Selective Magnetization Switching in the AA-Stacked VSiN3 Bilayer

The interplay between van Hove singularities (VHSs) and multiple degrees of freedom in two-dimensional materials offers a promising avenue for the discovery of emergent electronic and magnetic phases. Using first-principles calculations, we demonstrate that the AA-stacked VSiN3 bilayer is an ideal platform for exploring such physics. We find that the bilayer possesses an intrinsic out-of-plane polarization arising from interlayer charge transfer, which can be tuned via external strain and an electric field. Remarkably, VHSs appear at both the conduction band bottom (CBB) and the valence band top (VBT), exhibiting layer-dependent characteristics. The CBB is dominated by the top layer, whereas the VBT originates from the bottom layer. Upon carrier doping, this unique electronic structure drives a Stoner-type magnetic transition. In contrast to the stable magnetization found under hole doping, electron doping induces a complex, layer-selective spin polarization whose magnetization orientation is highly tunable by the doping concentration. This switchable magnetization allows for the reversal of valley polarization with the valley splitting consistently following the magnetization direction. Furthermore, this oscillatory magnetic and valleytronic behavior remains robust under a weak biaxial strain. Our results not only reveal a new mechanism for realizing doping-switchable magnetization and valley polarization in a nonmagnetic material but also establish the AA-stacked VSiN3 bilayer as a promising candidate for exploring the coupled properties of charge, spin, valley, and layer degrees of freedom.