Effects of different concentrations of topotactic hydrogen impurities on the electronic structure of nickelate superconductors

TL;DR

This paper investigates how varying concentrations of topotactic hydrogen impurities affect the electronic structure of nickelate superconductors, revealing optimal hydrogen levels that promote superconductivity.

Contribution

It introduces a theoretical multi-orbital Hubbard model to analyze the impact of hydrogen impurities on nickelate electronic states and superconductivity.

Findings

Low and high hydrogen concentrations induce high-spin states unfavorable for superconductivity.

Optimal 25% hydrogen concentration supports a single-band structure conducive to superconductivity.

Hydrogen impurities modulate inter-site hopping, influencing superconducting properties.

Abstract

Infinite-layer nickelate superconductors have recently been discovered to share both similarities and differences with cuprate superconductors. Notably, the incorporation of hydrogen (H) through topotactic reduction has been found to play a critical role in their electronic structure and, consequently, their superconductivity. In this study, we utilized a theoretical approach combining density-functional theory and impurity approximation to design three characteristic multi-orbital Hubbard models representing low, moderate, and high concentrations of topotactic-hydrogen. Consistent with experimental findings, our simulations revealed that both low and high concentrations of topotactic-hydrogen induce high-spin states ($S$=1) that are composed by holes at $d_{x^2-y^2}$ and $d_{z^2}$ orbitals and consequently the emergent inter-site hopping between $d_{z^2}$ to $d_{x^2-y^2}$ is unfavorable for superconductivity. Conversely, an optimal concentration of 25\% H aligns with the single Ni-$d_{x^2-y^2}$ band picture of superconductivity in infinite-layer nickelates, demonstrating its beneficial effect on promoting superconducting behavior.