A High Mobility Electron Gas at the LaA1O3/SrTiO3 Heterointerface

Polarity discontinuities at atomically abrupt crystalline heterointerfaces can lead to nontrivial local atomic and electronic structure, due to the presence of dangling bonds and incomplete coordinations1- 3. Originally discussed in semiconductors, these often arise in naturally occurring layered oxide structures, such as superconducting cuprates and ferroelectric titanates, as well as in artificial thin film oxide heterostructures such as manganite tunnel junctions4- 6. Here we have examined a model interface between two insulating perovskites, LaAlO3 and SrTiO3, controlling the termination layer at the interface on an atomic scale. In the simple ionic limit, this interface presents an extra half electron or hole per two-dimensional unit cell, depending on the structure of the interface - (LaO)+/(TiO2)0 for the first case, (AlO2)-/(SrO)0 for the later. Whereas the hole-doped interface is found to be insulating, the electron-doped interface is conducting, with extremely high carrier mobility exceeding 10,000 cm2/Vs. At low temperature, dramatic magnetoresistance oscillations periodic with the inverse magnetic field are observed, indicating quantum transport. This demonstrates that valence discontinuities at oxide interfaces can be engineered to construct novel charge states inaccessible in bulk materials.