Enabling triferroics coupling in breathing kagome lattice Nb3X8 (X = Cl, Br, I) monolayers

Abstract

Two-dimensional (2D) intrinsic multiferroic semiconductors have attracted considerable attention in recent years owing to their great prospects for future miniature information storage devices. Herein, based on first-principles calculations, we propose that the Nb₃X₈ (X = Cl, Br, I) monolayers with breathing kagome lattices are 2D intrinsic multiferroic semiconductors, which exhibit the coexistence of ferroelectricity, ferromagnetism, and ferrovalley. We found that the breathing process of kagome lattice trimer patterns corresponds to the out-of-plane ferroelectric polarization directions. More importantly, the magnetism of the Nb-trimer clusters can be generated and annihilated simultaneously at neighboring magnetic sites by reversing the direction of ferroelectric polarization due to magnetoelectric coupling. In addition, we demonstrate that the spontaneous valley polarization can be switched by reversing the direction of ferroelectric polarization or spin via the robust ferroelectricity–valley coupling or spin–valley coupling. Then, we design the switching of four different ferroelectric/ferromagnetic configurations, opening up a new insight into multistate storage devices. Our investigations reveal a microscopic mechanism of the coexistence and coupling between ferroelectricity, ferromagnetism, and ferrovalley in Nb₃X₈ (X = Cl, Br, I) monolayers, which provides a promising platform for manipulating the interaction of electron charge, spin, and valley degrees of freedom and the future multifunctional applications.