Engineered Mott ground state in LaTiO${}_{3+\delta }$/LaNiO${}_3$ heterostructure

In pursuit of creating cuprate-like electronic and orbital structures, artificial heterostructures based on LaNiO${}_3$ have inspired a wealth of exciting experimental and theoretical results. However, to date there is a very limited experimental understanding of the electronic and orbital states emerging after interfacial charge-transfer and their connections to the modified band structure at the interface. Towards this goal, we have synthesized a prototypical superlattice composed of correlated metal LaNiO${}_3$ and doped Mott insulator LaTiO${}_{3+\delta }$, and investigated its electronic structure by resonant X-ray absorption spectroscopy combined with X-ray photoemission spectroscopy, electrical transport and theory calculations. The heterostructure exhibits interfacial charge-transfer from Ti to Ni sites giving rise to an insulating ground state with orbital polarization and $e_{\text{g}}$ orbital band splitting. Our findings demonstrate how the control over charge at the interface can be effectively used to create exotic electronic, orbital and spin states.