MnIn2Se4 Bilayer: A Sliding Ferroelectric Topological Ferrimagnetic Metal with Triply-Coupled Switching

Sliding ferroelectric (FE) metals provide a practical route to combine switchable out-of-plane polarization with metallicity, yet realizing electrically reversible magnetization and Berry-curvature-driven anomalous transport and magneto-optical effects in a topological system remains challenging. Here, we establish a symmetry-based framework for sliding FE metals with ferrimagnetism. We show that interlayer sliding breaks the combined spin space symmetry, thereby inducing reversible out-of-plane polarization, nonrelativistic spin splitting, and finite net magnetization, namely, triply-coupled switching. Guided by this principle, we identify the MnIn2Se4 bilayer as a realistic sliding FE ferrimagnetic (FiM) metal hosting Weyl points, in which in-plane sliding enables robust triply-coupled switching, while spin-orbit coupling gaps the Weyl points and produces strong Berry curvature around the Fermi level, leading to large and electrically switchable anomalous transport and magneto-optical effects. Our results establish sliding FE FiM metals with topological states as a promising platform for electrically switchable, high-speed, and low-dissipation spintronic devices.