Ferroelectric metals in van der Waals bilayers

The combination of metallicity and ferroelectricity challenges conventional understanding, creating opportunities for advanced electronic materials and devices. This breakthrough is particularly notable, as metallicity and ferroelectricity have traditionally been considered mutually exclusive physical properties. In this work, starting with non-polar metallic single layers, we propose a design scheme for designing two-dimensional (2D) ferroelectric metals (FEMs) based on van der Waals interactions. By first-principles calculations, we also substantiate the feasibility of the design scheme in materials such as FeSe and H-MnTe2. Notably, this scheme unveils metallic ferroelectricity, characterized by reversing polarization through interlayer sliding. Furthermore, these systems exhibit a coexistence of inherent magnetism and sliding ferroelectricity. The investigated design scheme and observed phenomena have broad applicability across 2D materials. Our results not only advance research in 2D FEMs but also enhance the understanding of coupled physical phenomena in 2D lattices.