Multiferroic nematic d-wave altermagnetism driven by orbital-order on the honeycomb lattice

Altermagnets provide promising platforms for unconventional magnetism, whose controllability could enable a new generation of spintronic devices. While various bulk altermagnets have been discovered, altermagnetism in two-dimensional van der Waals materials remains elusive. Here we demonstrate that strained honeycomb monolayer VCl3 is an orbital-order-driven ferroelectric altermagnet. Whereas previous altermagnets rely on crystal and spin symmetries, the mechanism we uncover stems purely from electronic interactions, making it appealing for strongly correlated d-orbital systems. Using low-energy Hamiltonian and first-principles methods with symmetry analysis, we reveal a unique anti-ferro-orbital-antiferromagnetic phase characterized by 2D nematic d-wave altermagnetic spin splitting, tightly coupled with orbital-ordered induced ferroelectric polarization. Finally, through symmetry mode analysis, we show how structural distortions favor the interplay between orbital, altermagnetic, and ferroelectric degrees of freedom. Our study identifies VCl3 as a prototypical 2D orbital-order-driven multiferroic altermagnet on the honeycomb lattice, establishing a van der Waals monolayer featuring altermagnetic ferroelectricity.