Interface-induced Polarization in SrTiO$_3$-LaCrO$_3$ Superlattices

TL;DR

This study demonstrates how interface engineering in SrTiO$_3$-LaCrO$_3$ superlattices induces polarization throughout the non-polar SrTiO$_3$ layers, revealing mechanisms involving polar distortions and electric fields.

Contribution

It provides a detailed experimental and theoretical analysis of interface-induced polarization in SrTiO$_3$-LaCrO$_3$ superlattices, highlighting the role of interface structure.

Findings

Induced polarization extends across SrTiO$_3$ layers.

Displacements of Ti cations cause built-in potential gradients.

Intrinsic polar distortion and electric fields are due to charged interfaces.

Abstract

Epitaxial interfaces and superlattices comprised of polar and non-polar perovskite oxides have generated considerable interest because they possess a range of desirable properties for functional devices. In this work, emergent polarization in superlattices of SrTiO$_3$ (STO) and LaCrO$_3$ (LCO) is demonstrated. By controlling the interfaces between polar LCO and non-polar STO, polarization is induced throughout the STO layers of the superlattice. Using x-ray absorption near-edge spectroscopy and aberration-corrected scanning transmission electron microscopy displacements of the Ti cations off-center within TiO6 octahedra along the superlattice growth direction are measured. This distortion gives rise to built-in potential gradients within the STO and LCO layers, as measured by in situ x-ray photoelectron spectroscopy. Density functional theory models explain the mechanisms underlying this behavior, revealing the existence of both an intrinsic polar distortion and a built-in electric field, which are due to alternately positively and negatively charged interfaces in the superlattice. This study paves the way for controllable polarization for carrier separation in multilayer materials and highlights the crucial role that interface structure plays in governing such behavior.