Orbital engineering near La$_{2}$NiO$_{4}$-La$_{2}$CuO$_{4}$ superlattice interfaces

Orbital states of transition metal oxides present the opportunity of adjusting material properties to a specific purpose (orbital engineering). A comparison of the resonant soft x-ray reflectivity of La$_{2}$NiO$_{4}$-La$_{2}$CuO$_{4}$ superlattices at Ni L and Cu L edges shows different spatial distributions of the occupation of Ni d$_{x}$2$_{-y}$2 and d$_{3z}$2$_{-r}$2 orbitals in the LNO layers. This modulation of the Ni valence is possible through a pronounced modulation of the density of oxygen interstitial dopants within the structure which does not follow exactly the structure itself. This is the first observation of orbital engineering in a 214 oxide.