Switchable Electric Dipole from Polaron Localization in Dielectric Crystals

TL;DR

This paper predicts a switchable electric dipole in dielectric crystals caused by polaron localization, revealing a ferroelectric-like behavior that is distinct from traditional lattice polarization, with potential implications for tunable electronic properties.

Contribution

It introduces a novel ferroelectric-like dipole mechanism arising from polaron localization in doped dielectric crystals, analyzed via Berry phase and Hubbard U interactions.

Findings

A 6.15 Debye dipole is predicted in Sr3Ti2O7.

A double-well potential persists at high doping densities.

The defect state can transition from metallic to zero-dimensional polaron.

Abstract

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 ${\rm Sr_3Ti_2O_7}$. 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 ferroelectric-like behavior reported here is localized and distinct from conventional spontaneous lattice polarization.