Screening in a two-band model for superconducting infinite-layer nickelate

TL;DR

This paper explores how a two-band model for infinite-layer nickelates can be simplified to a single-band Hubbard model, revealing different regimes of electronic behavior influenced by screening effects and their implications for superconductivity.

Contribution

It demonstrates how screening of the itinerant s-band affects the correlation regime, leading to either a Mott insulator or a self-doped d-band, bridging one-band physics and Kondo-lattice-like behavior.

Findings

Weak screening results in a Mott insulating state with half-filled d orbitals.

Strong screening leads to a coupled s and d bands with potential d-wave pairing.

Mapping to a one-band model captures spectral weight transfer phenomena.

Abstract

Starting from an effective two-dimensional two-band model for infinite layered nickelates, consisting of bands obtained from $d$ and $s$--like orbitals, we investigate to which extend it can be mapped onto a single-band Hubbard model. We identify screening of the more itinerant $s$-like band as an important driver. In absence of screening one strongly-correlated band gives an antiferromagnetic ground state. For weak screening, the strong correlations push electrons out of the $s$-band so that the undoped nickelate remains a Mott insulator with half filled $d$ orbitals. This regime markedly differs from the observations in high-$T_c$ cuprates and pairing with $s$-wave symmetry would rather be expected in the superconducting state. In contrast, for strong screening, the $s$ and $d_{x^2-y^2}$ bands are both partly filled and couple only weakly, so that one approximately finds a self-doped $d$ band as well as tendencies towards $d$-wave pairing. Particularly in the regime of strong screening mapping to a one-band model gives interesting spectral weight transfers when a second $s$ band is also partly filled. We thus find that both one-band physics and a Kondo-lattice--like regime emerge from the same two-orbital model, depending on the strength of electronic correlations and the size of the $s$-band pocket.