Interface induced polar metals by multi-mode coupling*

Multi-mode coupling between various phonon modes in ABO₃ perovskite oxides can be tuned by forming heterostructures, which can lead to precise control of their functionalities [1]. Considering the interest in ferroelectric properties in a metal i.e., in polar metals [2], an efficient way to induce ferroelectric-like (FEL) displacements in the centrosymmetric phase is by interface-induced coupling [3]. Here, using first-principles density functional theory (DFT) and DFT+U (static d-d Coulomb interaction) we have investigated (BaTiO₃)_m/(Metal)_p/(BaTiO₃)_m' heterostructures [(m/p/m')= 6/3/7, 7/2/7, 7/1/8, m+p+m'= 16] to explore a new family of polar metals. We have chosen various metal blocks in a way that can represent a BTO/3dⁿ/BTO system, where n= 1-6. We found that a FEL phase coupled with in-plane rotation of BO₆ octahedra (a⁰a⁰c⁺) can be induced in the centrosymmetric 'metal' block when BaTiO₃ is in the ferroelectric phase. The properties are found to depend strongly on the relative polarization direction of BTO units. [1]. S. Ghosh et. al. Phys. Rev. B. 92, 184112, (2015), [2] S. Ghosh et. al. Phys. Rev. Lett. 119, 177603 (2017), [3] H. Guo, PNAS, 114, E5062-E5069 (2017).