Anomalous orbital structure in a spinel–perovskite interface

In all archetypical reported (001)-oriented perovskite heterostructures, it has been deduced that the preferential occupation of two-dimensional electron gases is in-plane d xy state. In sharp contrast to this, the investigated electronic structure of a spinel-perovskite heterostructure γ -Al 2 O 3 /SrTiO 3 by resonant soft X-ray linear dichroism, demonstrates that the preferential occupation is in out-of-plane d xz / d yz states for interfacial electrons. Moreover, the impact of strain further corroborates that this anomalous orbital structure can be linked to the altered crystal field at the interface and symmetry breaking of the interfacial structural units. Our findings provide another interesting route to engineer emergent quantum states with deterministic orbital symmetry. Complex oxides: Getting beneath the surface Symmetry is the key for high-temperature superconductivity at some oxide interfaces, say scientists in the United States and Germany. Yanwei Cao from the University of Arkansas (Jak Chakhalain's group) and co-workers used X-rays to investigate the electronic structure at a material boundary buried beneath the surface. The orbital symmetry of interfacial electrons in strontium titanate-based heterostructures is thought to be responsible for the emergence of unconventional superconductivity. But the exact electronic structure is unclear because most applicable measurement techniques can only look at the surface. They used an extremely sensitive method called resonant X-ray absorption spectroscopy to resolve the orbital symmetry at the strontium titanate–aluminum oxide interface. They found the orbital symmetry is reversed compared to that found in other materials in this family of so-called perovskite titanates.