Characteristic Lengths of Interlayer Charge Transfer in Correlated Oxide Heterostructures.

Using interlayer interaction to control functional heterostructures with atomic-scale designs has become one of the most effective interface-engineering strategies nowadays. Here, we demonstrate the effect of a crystalline LaFeO buffer layer on amorphous and crystalline LaAlO/SrTiO heterostructures. The LaFeO buffer layer acts as an energetically favored electron acceptor in both LaAlO/SrTiO systems, resulting in modulation of interfacial carrier density and hence metal-to-insulator transition. For amorphous and crystalline LaAlO/SrTiO heterostructures, the metal-to-insulator transition is found when the LaFeO layer thickness crosses 3 and 6 unit cells, respectively. Such different critical LaFeO thicknesses are explained in terms of distinct characteristic lengths of the redox-reaction-mediated and polar-catastrophe-dominated charge transfer, controlled by the interfacial atomic contact and Thomas-Fermi screening effect, respectively. Our results not only shed light on the complex interlayer charge transfer across oxide heterostructures but also provide a new route to precisely tailor the charge-transfer process at a functional interface.