Sliding Ferroic Multipoles in van der Waals Antiferromagnets

Non-relativistic spin splitting in altermagnets arises from the formation of a bipartite lattice of charge multipoles, where hybridisation with the local crystal environment lowers the on-site symmetry. For a generic antiferromagnetic (AFM) bilayer, simplified tight-binding models are used to show that interlayer hybridisation can regulate the local charge-multipolar order, imparting stacking- and twist-dependent spin splitting in stacked monolayers. DFT calculations for MnPSe3 bilayers confirms that this effect depends on both the overall bilayer symmetry and the local stacking order, and even permits different multipole symmetries at distinct interlayer registries. In bilayers with ferroelectric stacking orders, both the magnitude and symmetry of the on-site multipoles can be controlled through the application of an out-of-plane electric field, suggesting the possibility for electrically controlled altermagnetic response by exploiting lateral sliding at 2D antiferromagnetic interfaces.