Multiferroicity and Topology in Twisted Transition Metal Dichalcogenides

Van der Waals heterostructures have emerged as a highly versatile platform for sharpening our understanding of strong electronic correlations. We study topological flat bands of twisted transition metal dichalcogenides (TMDs) at odd integer fillings via exact diagonalization. We find that Chern insulator phases based on the non-interacting band structure are quite fragile, and give way to spontaneous multiferroic order - coexisting ferroelectricity and ferromagnetism, in presence of long-range Coulomb repulsion. We provide a simple real-space picture to understand the phase diagram as a function of interaction range and strength. Our findings establish twisted TMD homobilayers as a novel and highly tunable platform for multiferroicity, with potential applications to electrical control of magnetism.