Ferroelectricity in crystals is associated with the displacement of ions or rotations of polar units. Here we consider the dipole created by donor doping ($D^{+}$) and the corresponding bound polaron ($e^{-}$). A dipole of 6.15 Debye is predicted, from Berry phase analysis, in the Ruddlesden-Popper phase of ${\mathrm{Sr}}_3{\mathrm{Ti}}_2{\mathrm{O}}_7$. A characteristic double-well potential is formed, which persists for high doping densities. The effective Hubbard $U$ interaction can vary the defect state from metallic, a two-dimensional polaron, through to a zero-dimensional polaron. The ferroelectriclike behavior reported here is localized and distinct from conventional spontaneous lattice polarization.

• Received 16 February 2022
• Accepted 5 June 2022

DOI:https://doi.org/10.1103/PhysRevLett.129.017601