Electronically coupled complementary interfaces between perovskite band insulators.
Perovskite oxides exhibit a plethora of exceptional properties, providing the basis for novel concepts of oxide-electronic devices. The interest in these materials is even extended by the remarkable characteristics of their interfaces. Studies on single epitaxial connections between the wide-bandgap insulators LaAlO3 and SrTiO3 have revealed them to be either high-mobility electron conductors or insulating, depending on the atomic stacking sequences. For device applications, as well as for a basic understanding of the interface conduction mechanism, it is important to investigate the electronic coupling of closely spaced complementary interfaces. Here we report the successful realization of such coupled interfaces in SrTiO3-LaAlO3 thin-film multilayer structures. We found a critical separation distance of six perovskite unit cell layers, corresponding to approximately 23 A, below which a decrease of the interface conductivity and carrier density occurs. Interestingly, the high carrier mobilities characterizing the separate conducting interfaces are found to be maintained in coupled structures down to subnanometre interface spacing.