Co valence transformation in isopolar LaCo O₃/LaTi O₃ 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 LaTiO₃ to the charge transfer insulator LaCoO₃. 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 LaTiO₃ and LaCoO₃, and the LaCoO₃ film thickness itself in trilayers provide a trio of control knobs for average charge of the cobalt ions in LaCoO₃, illustrating the efficacy of O-2p band alignment as a guiding principle for property design in complex oxide heterointerfaces.