Co valence transformation in isopolar<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>LaCo</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:mo>/</mml:mo><mml:mi>LaTi</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>perovskite heterostructures via interfacial engineering
Georgios Araizi-Kanoutas, Jaap Geessinck, Nicolas Gauquelin, Steef Smit, Xanthe H. Verbeek, Shrawan K. Mishra, Peter Bencok, Christoph Schlueter, Tien-Lin Lee, Dileep Krishnan, Jarmo Fatermans, Jo Verbeeck, Guus Rijnders, Gertjan Koster, Mark S. Golden
Abstract
We report charge transfer up to a single electron per interfacial unit cell across nonpolar heterointerfaces from the Mott insulator $\mathrm{LaTi}{\mathrm{O}}_{3}$ to the charge transfer insulator $\mathrm{LaCo}{\mathrm{O}}_{3}$. In high-quality bi- and trilayer systems grown using pulsed laser deposition, soft x-ray absorption, dichroism, and scanning transmission electron microscopy-electron energy loss spectroscopy are used to probe the cobalt-$3d$ electron count and provide an element-specific investigation of the magnetic properties. The experiments show the cobalt valence conversion is active within 3 unit cells of the heterointerface, and able to generate full conversion to $3{d}^{7}$ divalent Co, which displays a paramagnetic ground state. The number of $\mathrm{LaTi}{\mathrm{O}}_{3}/\mathrm{LaCo}{\mathrm{O}}_{3}$ interfaces, the thickness of an additional, electronically insulating ``break'' layer between the $\mathrm{LaTi}{\mathrm{O}}_{3}$ and $\mathrm{LaCo}{\mathrm{O}}_{3}$, and the $\mathrm{LaCo}{\mathrm{O}}_{3}$ film thickness itself in trilayers provide a trio of control knobs for average charge of the cobalt ions in $\mathrm{LaCo}{\mathrm{O}}_{3}$, illustrating the efficacy of $O\ensuremath{-}2p$ band alignment as a guiding principle for property design in complex oxide heterointerfaces.