Self-doped Mott insulator for parent compounds of nickelate superconductors

TL;DR

This paper proposes that the parent compound of nickelate superconductors is a self-doped Mott insulator with Kondo singlet formation, explaining its normal state properties and the emergence of superconductivity upon doping.

Contribution

It introduces a novel model of the parent nickelate compound as a self-doped Mott insulator with Kondo physics, providing a theoretical framework for understanding its superconductivity.

Findings

Resistivity and Hall data show logarithmic temperature dependence.

A generalized t-J model with Kondo singlets explains suppressed magnetic order.

Doping increases holons, leading to superconductivity and strange metal behavior.

Abstract

We propose the parent compound of the newly discovered superconducting nickelate Nd$_{1-x}$Sr$_{x}$NiO$_{2}$ as a self-doped Mott insulator, in which the low-density Nd-$5d$ conduction electrons couple to localized Ni-3$% d_{x^{2}-y^{2}}$ 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 $t$-$J$ model with both Kondo singlets and nickel holons moving through the lattice of 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.