Dual instability of superconductivity from oxygen defects in La$_3$Ni$_2$O$_{7+\delta}$

TL;DR

This study reveals how oxygen defects in La$_3$Ni$_2$O$_{7+eta}$ suppress superconductivity through dual mechanisms involving disorder and interstitial ordering, providing insights for defect engineering to enhance superconducting properties.

Contribution

It identifies the specific roles of apical vacancies and interstitials in affecting superconductivity in bilayer nickelates using advanced theoretical methods.

Findings

Oxygen vacancies induce local magnetic moments and localization.

Interstitial ordering creates a metallic background incompatible with superconductivity.

Defects critically influence the electronic structure and superconducting behavior.

Abstract

We uncover a dual mechanism by which oxygen defects suppress superconductivity in the bilayer nickelate La$_3$Ni$_2$O$_{7+\delta}$ using density functional theory, dynamical mean-field theory, and functional renormalization group analysis. Apical vacancies and interbilayer interstitials emerge as the dominant low-energy defect species and are further stabilized by orthorhombic domain walls. These two defect classes drive the electronic structure in opposing directions. Vacancy-induced disorder generates local magnetic moments and promotes Anderson localization at moderate concentrations, whereas periodic interstitial ordering yields a coherent but weakly correlated metallic background that fails to support superconductivity. These findings highlight the decisive role of oxygen defects in shaping the superconducting and provide microscopic guidance for improving superconductivity through controlled defect engineering.