No abstract

High-mobility electron gases in SrTiO3-based heterostructures have been mainly synthesized on single TiO2 terminated SrTiO3 substrates. Here, we show a high-mobility electron gas observed in a Sr2TiO4/SrTiO3 heterostructure based on an untreated SrTiO3 substrate with mixed termination, showing the mobility value up to 28 000 cm2 V−1 s−1 at 2 K. SrO–SrO vertical Ruddlesden–Popper faults in the Sr2TiO4 film provide escape channels for oxygen atoms under high temperatures, enabling the as-grown tuning of oxygen vacancies in the SrTiO3 layer during film deposition and reversible after-growth modulation in a thermal annealing process.

Charge transfer in perovskite oxide heterostructures could break the delicate balance among charge, spin, orbital and lattice order at the interface, producing exotic phenomena that cannot be observed in bulk materials. Here, opposite interfacial charge transfer directions are observed in SrIrO3/NdNiO3 and SrIrO3/LaNiO3 3d/5d perovskite heterostructures. This is accompanied with an inverse change of Ni eg orbital polarization and Ni-O pd hybridization across the interface, by stretching/compressing the out-of-plane Ni-O bond in the opposite internal electrical field due to the opposite electron transfer direction. These interfacial reconstructions finally bring about a manipulation on the transport and magnetic characteristics. This work reveals that A site cation in perovskite heterostructures could be a knob to control the interfacial charge transfer direction, and the 3d/5d perovskite interfaces are excellent platform to study the complex interplay between various order parameters and stimulate novel interfacial effects.