We propose the parent compound of the newly discovered superconducting nickelate ${\mathrm{Nd}}_{1-x}{\mathrm{Sr}}_x{\mathrm{NiO}}_2$ as a self-doped Mott insulator, in which the low-density Nd $5d$ conduction electrons couple to localized Ni $3d_{x^2-y^2}$ electrons to form Kondo spin singlets at low temperatures. This proposal is motivated with our analyses of the reported resistivity and Hall coefficient data in the normal state, showing logarithmic temperature dependence at low temperatures. In the strong Kondo coupling limit, we derive a generalized $t\text{−}J$ model with both Kondo singlets and nickel holons moving through the lattice of an otherwise nickel spin-1/2 background. The antiferromagnetic long-range order is therefore suppressed as observed in experiments. With Sr doping, the number of holons on the nickel sites increases, giving rise to the superconductivity and a strange metal phase analogous to those in superconducting copper oxides.

• Received 29 September 2019

DOI:https://doi.org/10.1103/PhysRevB.101.020501