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

Peiheng Jiang, Jie Li, Yu-Han Cao, Xiaodong Cao, Zhicheng Zhong, Yi Lu, Qiang-Hua Wang

Abstract

We uncover a dual mechanism by which oxygen defects suppress superconductivity in the bilayer nickelate La$_3$Ni$_2$O$_{7+δ}$ 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.

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

Abstract

We uncover a dual mechanism by which oxygen defects suppress superconductivity in the bilayer nickelate LaNiO 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.

Paper Structure

This paper contains 3 figures, 1 table.

Figures (3)

  • Figure 1: (a) Schematic structures of oxygen defects in La$_3$Ni$_2$O$_{7}$. The dashed box marks the boundary between two orthorhombic domains. (b, c) DFT+$U$ band structures of (b) pristine La$_3$Ni$_2$O$_{7}$ and (c) La$_3$Ni$_2$O$_{7.25}$. Cyan, magenta, and green indicate Ni $d_{x^2-y^2}$, $d_{3z^2-r^2}$, and O $p$ orbital character, respectively.
  • Figure 2: DMFT spectral functions (a-d) and self-energies (e-h) for La$_3$Ni$_2$O$_{7}$ [(a),(e)], La$_3$Ni$_2$O$_{6.5}$ [(b),(f) pyramidal sites; (c),(g) octahedral sites], and La$_3$Ni$_2$O$_{7.5}$ [(d),(h)] under ambient pressure (AP, 0 GPa) and high pressure (HP, 20 GPa). Insets in panels (a-d) show the imaginary-time spin-spin correlation functions $\chi_{zz}(\tau) = \langle S_z(\tau) S_z(0) \rangle$, where $S_z$ is the total $z$ spin component of the $d_x$ and $d_z$ orbitals.
  • Figure 3: Critical scales $\Lambda_c$ as a function of $J_H$ for different $U$ values in (a) La$_3$Ni$_2$O$_{7.5}$ and (b) La$_3$Ni$_2$O$_{7}$. Panels (c) and (d) show representative flows of the singular values $S$ in the SC, SDW, and CDW channels for $(U, J_H) = (3.0, 0.5)$ eV in La$_3$Ni$_2$O$_{7.5}$ and La$_3$Ni$_2$O$_{7}$, respectively.