Comparative study of charge order in undoped infinite-layer nickelate superconductors

TL;DR

This study uses advanced computational methods to analyze charge order phenomena in infinite-layer nickelate superconductors, revealing the role of a free electron chain in enhancing charge order and suggesting potential implications for superconductivity.

Contribution

It introduces a minimal three-legged model combining a Hubbard ladder and a free electron chain, showing how the latter enhances charge order in nickelates.

Findings

Long-range charge order with period 3 observed in the model.

Electron pair correlations indicate potential superconducting instability.

The free electron chain acts as a charge reservoir, strengthening charge order.

Abstract

To understand the microscopic mechanism of the charge order observed in the parent compound of the infinite-layer nickelate superconductors, we consider a minimal three-legged model consisting of a two-legged Hubbard ladder for the Ni $3d_{x^2-y^2}$ electrons and a free conduction electron chain from the rare-earths. With highly accurate density matrix renormalization group calculations, when the chemical potential difference is adjusted to make the Hubbard ladder with $1/3$ hole doping, we find a long-range charge order with period $3$ in the ground state of the model, while the spin excitation has a small energy gap. Moreover, the electron pair-pair correlation has a quasi-long-range behavior, indicating an instability of superconductivity even at half-filling. As a comparison, the same method is applied to a pure two-legged Hubbard model with $1/3$ hole doping in which the period-3 charge order is a quasi-long range one. The difference between them demonstrates that the free electron chain of the three-legged ladder plays the role of a charge reservoir and enhances the charge order in the undoped infinite-layer nickelates.