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 La$X$O${}_3$ ($X$=Al, Ga, Sc) into La${}_2$NiO${}_4$, the extra (LaO)${}^{+}$ layers act as electron donors, releasing carriers into the Ni-3$d$ 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.