Heterostructuring as Gateway to Electron Doping of Nickelate Superconductors.

Despite enormous expenditures in the research field, the electron-doped side of nickelate superconductors remains uncharted territory. Substituting the trivalent rare-earth cations by a tetravalent one hitherto failed. Here, we demonstrate by first-principles calculations a disorder-free route to electron dope Ruddlesden-Popper nickelates. When intercalating wide-band-gap insulating layers such as LaXO_{3} (X=Al, Ga, Sc) into La_{2}NiO_{4}, the extra (LaO)^{+} layers act as electron donors, releasing carriers into the Ni-3d orbitals. This electron doping puts La_{2}NiO_{4}:La_{2}AlO_{4} naturally in the optimal region for d_{x^{2}-y^{2}}-wave superconductivity with T_{c} exceeding 50 K. The same concept also allows us to electron dope La_{3}Ni_{2}O_{7}, the superconductor in the limelight.