Effective Hamiltonian for superconducting Ni oxides Nd$_{1-x}$Sr$_x$NiO$_2$

TL;DR

This paper derives an effective one-band Hamiltonian for Nd$_{1-x}$Sr$_x$NiO$_2$, revealing its nature as a doped Mott insulator with specific hopping and exchange parameters, and discusses electronic structure features like self-doping and heavy fermion behavior.

Contribution

The study provides a first-principles derivation of a one-band $t$-$t'$-$J$ model for nickelate superconductors, connecting electronic structure calculations with effective low-energy models.

Findings

NiO$_2$ plane is a Hubbard Mott insulator.

Doped holes mainly locate on Ni sites.

Parameters for the $t$-$t'$-$J$ model are quantified.

Abstract

We derive the effective single-band Hamiltonian in the flat NiO$_2$ planes for nickelate compounds Nd$_{1-x}$Sr$_x$NiO$_2$. We first implement the first-principles calculation to study electronic structures of nickelates using the Heyd-Scuseria-Ernzerhof hybrid density functional and derive a three-band Hubbard model for Ni-O $pd\sigma$ bands of Ni$^+$ $3d_{x^2-y^2}$ and O$^{2-}$ $2p_{x/y}$ orbitals in the NiO$_2$ planes. To obtain the effective one-band $t$-$t'$-$J$ model Hamiltonian, we perform the exact diagonalization of the three-band Hubbard model for the Ni$_5$O$_{16}$ cluster and map the low-energy spectra onto the effective one-band models. We find that the undoped NiO$_2$ plane is a Hubbard Mott insulator, and the doped holes primarily locate on Ni sites. The physics of the NiO$_2$ plane is a doped Mott insulator, described by the one-band $t$-$t'$-$J$ model with $t=265$~meV, $t'=-21$~meV and $J=28.6$~meV. We also discuss the electronic structure for the "self-doping" effect and heavy fermion behavior of electron pockets of Nd$^{3+}$ $5d$ character in Nd$_{1-x}$Sr$_x$NiO$_2$.