[Paper Review] Superconductivity in a minimal two-band model for infinite-layer nickelates.

Peng Cheng, Hong‐Chen Jiang+3 more|arXiv (Cornell University)|Oct 14, 2021

Physics of Superconductivity and Magnetism35 references4 citations

TL;DR

This study investigates superconductivity in a minimal two-band Hubbard model for infinite-layer nickelates using density-matrix renormalization group (DMRG) on four-leg cylinders. It finds that at 12.5% hole doping, the system exhibits Luther-Emery liquid behavior with power-law superconducting and charge density correlations in the Ni layer, consistent with experimental observations of unconventional superconductivity.

ABSTRACT

While the recent discovery of superconductivity in infinite-layer nickelates has drawn considerable attention, a common ingredient of the fundamental building blocks to describe their ground states has been lacking. A series of experimental and theoretical studies have suggested that an effective two-band Hubbard model with Ni 3$d_{x^2-y^2}$ and rare-earth ($R$) 5$d$ character may describe the low-energy physics. Here, we study the ground state properties of this two-band model on four-leg cylinders using the density-matrix renormalization group (DMRG). At half-filling, the ground state of the system is consistent with a Luttinger liquid, possessing quasi-long-range charge and spin correlations in the $R$ layer, but short-range correlations in the Ni layer. At a hole doping concentration of $\delta=12.5\%$, the $R$ layer is nearly empty and the ground state of the system is consistent with a Luther-Emery liquid, where we find power-law superconducting and charge density correlations in the Ni layer, but exponentially decaying spin correlations. The consistency of our results with experimental observations may help to reveal the microscopic mechanism for pairing in these nickelates and other unconventional superconductors.

Motivation & Objective

• To identify the minimal effective model capturing low-energy physics in infinite-layer nickelates.
• To investigate the emergence of superconductivity in a two-band system with Ni 3d and rare-earth 5d orbital character.
• To determine the nature of the ground state at hole doping using numerically exact DMRG simulations.
• To connect theoretical results with experimental observations of superconductivity in nickelates.

Proposed method

• A two-band Hubbard model is formulated with Ni 3d_{x^2-y^2} and rare-earth 5d orbital degrees of freedom.
• The model is solved numerically using the density-matrix renormalization group (DMRG) on four-leg cylindrical lattices.
• Ground state properties are analyzed via correlation functions: charge, spin, and superconducting correlations.
• The system is studied at half-filling and at 12.5% hole doping to probe phase transitions and pairing tendencies.
• Correlation decay behavior (power-law vs. exponential) is used to classify the ground state as Luttinger or Luther-Emery liquid.

Experimental results

Research questions

• RQ1 What is the nature of the ground state in a minimal two-band model for infinite-layer nickelates at half-filling?
• RQ2 How does hole doping affect the emergence of superconducting and charge density correlations in the Ni layer?
• RQ3 Does the system exhibit Luther-Emery liquid behavior at 12.5% hole doping, as indicated by power-law superconducting correlations?
• RQ4 Are the predicted correlation behaviors consistent with experimental observations of superconductivity in nickelates?
• RQ5 What role do the rare-earth 5d orbitals play in mediating or stabilizing superconducting pairing?

Key findings

• At half-filling, the system exhibits Luttinger liquid behavior with quasi-long-range charge and spin correlations in the rare-earth layer, but short-range correlations in the Ni layer.
• At 12.5% hole doping, the ground state is consistent with a Luther-Emery liquid, characterized by power-law superconducting and charge density correlations in the Ni layer.
• Spin correlations decay exponentially in the Ni layer at 12.5% doping, indicating spin gap formation.
• The rare-earth layer becomes nearly empty at 12.5% hole doping, suggesting a decoupling of spin degrees of freedom from the Ni layer.
• The observed power-law superconducting correlations in the Ni layer are consistent with experimental reports of superconductivity in nickelates.