Orbital Reconstruction and Covalent Bonding at an Oxide Interface

Modern microelectronics relies to a large degree on the properties ofinterfaces between two different semiconductors. For example, atransistor is commonly formed from the electronic interactions at such an interface, and its electrical conductivity can be controlled very ef-fectively by application of an external voltage to its gate electrode. Optimizing the operation of transistors and othermicroelectronic devices requires knowledge of the electronic states near semiconductor interfaces, and many details have been revealed over the past half-century. Key to recent developments has been the ability to create high-quality atomically abrupt interfaces between different materials, including complex oxides with intricate or large unit cells. In bulk, these oxides show rich and varied electronic and magnetic properties produced by strong interactions among the electrons (1). Combining these materials along an interface can produce new quantum states and the opportunity to uncover unexpected phenomena. We outline steps toward visualizing and resolving the detailed behavior of electrons in specific orbitals at the interface between two complex mate-rials.We studied twomaterials exhibiting properties not known in ordinar