Three dimensional band-filling control of complex oxides triggered by interfacial electron transfer

The d -band-filling of transition metals in complex oxides plays an essential role in determining their structural, electronic and magnetic properties. Traditionally, at the oxide heterointerface, band-filling control has been achieved via electrostatic modification in the structure of field-effect transistors or electron transfer, which is limited to the quasi-two-dimension at the interface. Here we report a three-dimensional (3D) band-filling control by changing the local lattice coordination in a designed oxide heterostructure. At the LaCoO 3 /LaTiO 3 heterointerface, due to the Fermi level mismatch, electrons transfer from LaTiO 3 to LaCoO 3 . This triggers destabilisation of the CoO 6 octahedrons, i.e. the formation of lattice configurations with a reduced Co valence. The associated oxygen migration results in the 3D topotactic phase transition of LaCoO 3 . Tuned by the thickness of LaTiO 3 , different crystalline phases and band-fillings of Co occur, leading to the emergence of different magnetic ground states. Band-filling control of transition metal ions in oxide heterostructures is typically limited to the two-dimensional interface. Here, the authors report a three-dimensional modulation of the band-filling and a topotactic phase transition in LaCoO 3 , triggered by charge transfer at LaCoO 3 /LaTiO 3 interface.