Charge disproportionation driven polar magnetic metallic double-layered perovskite Sr₃Co₂O₇

Strong coupling among spontaneous structural symmetric breaking, magnetism and metallicity in an intrinsic polar magnetic metal can give rise to novel physical phenomena and holds great promise for applications in spintronics. Here, we elucidate the mechanism of magnetic polarity in the recently discovered polar metal Sr₃Co₂O₇. Our first-principles calculations reveal that both the spontaneous polar displacements and the metallicity originate from charge disproportionation of Co ions. This is characterized by an inverted ligand-field splitting of the Co t_2g orbitals at one site, while the metallic behavior is preserved by the t_2g orbitals at both sites. Charge disproportionation, which originates from the on-site Hubbard U interaction, stabilizes the asymmetric phase. We thus propose that in related transition metal oxides, charge disproportionation within specific orbitals can concurrently drive metallicity and polarity, enabling strong coupling between these properties. More remarkably, this mechanism allows for the coexistence of magnetism, as evidenced in Sr₃Co₂O₇. Our findings highlight a promising avenue for realizing polar magnetic metals and provide a new design principle for exploring multifunctional materials.