Polar Charge-Ordered States in BiFeO$_3$/CaFeO$_3$ Superlattice

TL;DR

This paper explores the structural and electronic properties of BiFeO$_3$/CaFeO$_3$ superlattices, revealing a polar charge-ordered state with potential for multifunctional electronic applications through interface and strain engineering.

Contribution

It introduces a novel polar charge-ordered phase in BiFeO$_3$/CaFeO$_3$ superlattices stabilized by lattice instabilities and symmetry coupling, combining ferroelectricity and antiferromagnetism.

Findings

Stabilization of a non-centrosymmetric $Pc$ ground state with polar charge order.

Coexistence of C-type antiferromagnetism and ferroelectric semiconductor behavior.

Calculated band gap of approximately 0.6 eV.

Abstract

Oxide superlattices represent a potent avenue for tailoring emergent electronic phases through sophisticated interfacial charge transfer and dynamic lattice distortions. This study systematically investigates the structural and electronic attributes of the BiFeO$_3$/CaFeO$_3$ superlattice, leveraging a comprehensive approach that integrates first-principles computations with detailed symmetry-mode analysis. The strategic integration of polar bismuth ferrite alongside charge-transfer calcium ferrite instigates profound lattice instabilities, notably manifest in octahedral rotations and cooperative FeO$_6$ breathing modes that might not necessarily be soft. However, their synergistic coupling stabilizes a non-centrosymmetric $Pc$ ground state that intrinsically features polar charge ordering of Fe ions. This resultant phase ingeniously unifies C-type antiferromagnetism with robust ferroelectric semiconductor characteristics, exhibiting a calculated indirect band gap of about 0.6 eV. Our discoveries firmly establish ferrite superlattices as an exceptionally versatile and tunable platform for the rational design of next-generation multifunctional materials, offering precise control over polarization, charge ordering phenomena, and electronic transport behavior via advanced interface and strain engineering techniques.