Electron-lattice coupling contributions to polarization switching in charge-order-induced ferroelectrics

TL;DR

This study uses first-principles calculations to explore how electron-lattice interactions influence polarization switching in charge-order-induced ferroelectrics, revealing mechanisms that depend on lattice relaxation and charge ordering type.

Contribution

It classifies charge-ordering ferroelectrics into two types based on lattice mode coupling and explains the conditions for non-adiabatic switching, advancing understanding of electronic ferroelectricity.

Findings

Lattice relaxation can lock charge-order states, hindering switching.

Non-adiabatic electron hopping occurs only in off-centering displacement ferroelectrics.

Different switching behaviors in LuFe₂O₄ and Fe₃O₄ are explained.

Abstract

We carry out first-principles density-functional-theory calculations to elucidate the polarization switching mechanism in charge-ordering-induced ferroelectrics based on the prototypical case of the (SrVO$_3$)$_1$(LaVO$_3$)$_1$ superlattice. We find that lattice relaxation for a specific charge ordering state can "lock" that state in, making non-adiabatic switching to a different CO variant energetically prohibitive, and in some cases, even making the energy barrier for adiabatic switching prohibitively large. We classify charge-ordering materials into two types, polyhedral breathing and off-centering displacement, based on the type of lattice mode most strongly coupled to the charge ordering. We demonstrate that the non-adiabatic electron hopping induced by an external electric field is expected only in off-centering-displacement-type charge-ordering-induced ferroelectrics. This successfully explains the different observed switching behaviors of LuFe$_2$O$_4$ and Fe$_3$O$_4$. These results offer a new understanding of the polarization switching mechanism in charge-ordering-induced ferroelectrics that provides guidance for the design and discovery of charge-ordering-induced ferroelectric materials and suggests a strategy for realizing "electronic ferroelectricity" with polarization switching on electronic rather than lattice time scales.