Polar and electronic phase control through interacting structural modes

Abstract We demonstrate the control of coupled structural, electronic, and magnetic degrees of freedom in oxide superlattices using ( LaFeO 3 ) 1 / ( CaFeO 3 ) 1 as a concrete model system. Combining symmetry-mode analysis, first-principles density functional theory calculations, Berry-phase polarization with phonon computations with density functional perturbation theory, we uncover a previously unrecognized polar A-type charge-disproportionation mode Q ACD that couples to the hybrid-improper trilinear polar mode Q Tri . This multimode interaction Q M ∼ Q Tri Q ACD lowers the symmetry to polar Pc within the C-type antiferromagnetic ordering and generates a rich phase space comprising polar metallic , semimetallic , and insulating ground states. A two-parameter Landau-type energy map E ( Q Tri , Q ACD ) reveals four symmetry-related polarization domains while both Q Tri and Q ACD set the direction of the spontaneous polarization. Q ACD controls a tunable electronic structure leading to insulator → metal → insulator evolution, accompanied by a controllable sublattice magnetization contrast. Taking several 3 d − 4 d transition metals in the B- and B′-sublattices as prototype examples, our study showcases that the proposed design principle is generalizable across a broad class of transition metal oxide superlattices with Pnma -type building blocks and partially filled e _g or t 2 g orbitals, offering a promising route toward engineering multifunctional quantum phases in oxide interfaces.