Co valence transformation in isopolar LaCoO$_{3}$/LaTiO$_{3}$ perovskite heterostructures via interfacial engineering

We report charge transfer up to a single electron per interfacial unit cell across nonpolar heterointerfaces from the Mott insulator LaTiO$_{3}$ to the charge transfer insulator LaCoO$_{3}$. 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 3d7 divalent Co, which displays a paramagnetic ground state. The number of LaTiO3/LaCoO3 interfaces, the thickness of an additional, electronically insulating “break” layer between the LaTiO$_{3}$ and LaCoO$_{3}$, and the LaCoO$_{3}$ film thickness itself in trilayers provide a trio of control knobs for average charge of the cobalt ions in LaCoO$_{3}$, illustrating the efficacy of O−2p band alignment as a guiding principle for property design in complex oxide heterointerfaces