Designing nickelate superconductors with $d^8$ configuration exploiting mixed-anion strategy

TL;DR

This paper proposes a theoretical design for a new nickelate superconductor with a $d^8$ electron configuration, using a mixed-anion strategy to enhance superconductivity by manipulating orbital energy differences.

Contribution

The study introduces a novel approach to designing nickelate superconductors with $d^8$ configuration by employing mixed-anion strategies to modify orbital energies.

Findings

Enlarging the energy difference between $3d_{x^2-y^2}$ and other $3d$ orbitals promotes superconductivity.

Incorporating halogens or hydrogen as out-of-plane anions creates incipient bands near the Fermi level.

The proposed design may be relevant to the recently discovered (Nd,Sr)NiO$_2$ superconductor.

Abstract

Inspired by a recently proposed superconducting mechanism for a new cuprate superconductor Ba$_2$CuO$_{3+\delta}$, we theoretically design an unconventional nickelate superconductor with $d^8$ electron configuration. Our strategy is to enlarge the on-site energy difference between $3d_{x^2-y^2}$ and other $3d$ orbitals by adopting halogens or hydrogen as out-of-plane anions, so that the $3d$ bands other than $d_{x^-y^2}$ lie just below the Fermi level for the $d^8$ configuration, acting as incipient bands that enhance superconductivity. We also discuss a possible relevance of the present proposal to the recently discovered superconductor (Nd,Sr)NiO$_2$.