Hybridization-controlled charge transfer and induced magnetism at correlated oxide interfaces

TL;DR

This study reveals how covalence and hybridization effects influence charge transfer and magnetism at correlated oxide interfaces, demonstrating new pathways to engineer novel electronic phases.

Contribution

It identifies covalence alteration as a key factor in charge transfer at correlated oxide interfaces, expanding the classical band alignment framework.

Findings

Charge transfer is affected by hybridization effects tuned by rare-earth size.

Charge transfer induces ferromagnetic-like states in nickelates.

Strategies for engineering 2D systems through doping and covalence control.

Abstract

At interfaces between conventional materials, band bending and alignment are classically controlled by differences in electrochemical potential. Applying this concept to oxides in which interfaces can be polar and cations may adopt a mixed valence has led to the discovery of novel two-dimensional states between simple band insulators such as LaAlO3 and SrTiO3. However, many oxides have a more complex electronic structure, with charge, orbital and/or spin orders arising from correlations between transition metal and oxygen ions. Strong correlations thus offer a rich playground to engineer functional interfaces but their compatibility with the classical band alignment picture remains an open question. Here we show that beyond differences in electron affinities and polar effects, a key parameter determining charge transfer at correlated oxide interfaces is the energy required to alter the covalence of the metaloxygen bond. Using the perovskite nickelate (RNiO3) family as a template, we probe charge reconstruction at interfaces with gadolinium titanate GdTiO3. X-ray absorption spectroscopy shows that the charge transfer is thwarted by hybridization effects tuned by the rare-earth (R) size. Charge transfer results in an induced ferromagnetic-like state in the nickelate, exemplifying the potential of correlated interfaces to design novel phases. Further, our work clarifies strategies to engineer two-dimensional systems through the control of both doping and covalence.