Abstract
In all archetypical reported (001)-oriented perovskite heterostructures, it has been deduced that the preferential occupation of twodimensional electron gases is in-plane dxy state. In sharp contrast to this, the investigated electronic structure of a spinel-perovskite heterostructure gamma-Al2O3/SrTiO3 by resonant soft X-ray linear dichroism, demonstrates that the preferential occupation is in out-ofplane 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.