Full control of Co valence in isopolar LaCoO3 / LaTiO3 perovskite heterostructures via interfacial engineering

TL;DR

This study demonstrates precise control of cobalt valence states in LaCoO3/LaTiO3 heterostructures through interfacial engineering, enabling full charge transfer and magnetic state manipulation at the atomic scale.

Contribution

It introduces a method to deterministically tune charge transfer and valence states in complex oxide heterostructures via interface design and layer thickness control.

Findings

Charge transfer of up to one electron per interfacial unit cell.

Full conversion of Co to a 3d7 divalent state within three unit cells.

Charge transfer can be controlled by interface number, break layer thickness, and film thickness.

Abstract

We report charge-transfer up to a single electron per interfacial unit cell across non-polar heterointerfaces from the Mott insulator LaTiO3 to the charge transfer insulator LaCoO3. In high-quality bi- and tri-layer systems grown using pulsed laser deposition, soft X-ray absorption, dichroism and STEM-EELS are used to probe the cobalt 3d-electron count and provide an element-specific investigation of the magnetic properties. The experiments prove a deterministically-tunable charge transfer process acting in the LaCoO3 within three unit cells of the heterointerface, 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 "break" layer between the LaTiO3 and LaCoO3, and the LaCoO3 film thickness itself in tri-layers provide a trio of sensitive control knobs for the charge transfer process, illustrating the efficacy of O2p-band alignment as a guiding principle for property design in complex oxide heterointerfaces.