Electronic properties of the bilayer nickelates <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>R</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:mi mathvariant="normal">N</mml:mi><mml:msub><mml:mi mathvariant="normal">i</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>7</mml:mn></mml:msub></mml:mrow></mml:math> with oxygen vacancies (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>R</mml:mi><mml:mo>=</mml:mo><mml:mi>La</mml:mi></mml:mrow></mml:math> or Ce)

Abstract

The discovery of superconductivity in $\mathrm{L}{\mathrm{a}}_{3}\mathrm{N}{\mathrm{i}}_{2}{\mathrm{O}}_{7}$ has sparked significant research interest in the field of nickelate superconductors. Despite extensive studies on pristine $\mathrm{L}{\mathrm{a}}_{3}\mathrm{N}{\mathrm{i}}_{2}{\mathrm{O}}_{7}$, the role of oxygen vacancies (${V}_{\mathrm{O}}$), a common type of intrinsic defect in oxides, on electronic structures and superconductivity in $\mathrm{L}{\mathrm{a}}_{3}\mathrm{N}{\mathrm{i}}_{2}{\mathrm{O}}_{7}$ remains unclear. In this paper, we identify that the loss of intrabilayer apical oxygen is the most energetically favorable. The electronic structure undergoes notable changes, particularly for the Ni-${d}_{z2}$ and Ni-${d}_{x2\ensuremath{-}y2}$ orbitals. The ${d}_{z2}$ orbital shifts downward, substantially reducing its proportion at the Fermi level. Conversely, the proportion of the ${d}_{x2\ensuremath{-}y2}$ state increases due to the orbital localization. Applying the two-band model, the hopping strength between intrabilayer ${d}_{z2}$ functions is observed to increase significantly but with opposite signs, which deviates from the previous understanding. The interorbital hopping between ${d}_{z2}$ and ${d}_{x2\ensuremath{-}y2}$ functions decreases in the presence of ${V}_{\mathrm{O}}$. Our results indicate that the formation of ${V}_{\mathrm{O}}$ could be harmful to the superconductivity in $\mathrm{L}{\mathrm{a}}_{3}\mathrm{N}{\mathrm{i}}_{2}{\mathrm{O}}_{7}$, considering the general assumption regarding the critical role of ${d}_{z2}$ in superconductivity generation. Additionally, we propose that $\mathrm{C}{\mathrm{e}}_{3}\mathrm{N}{\mathrm{i}}_{2}{\mathrm{O}}_{7}$, possessing similar electronic structures to $\mathrm{L}{\mathrm{a}}_{3}\mathrm{N}{\mathrm{i}}_{2}{\mathrm{O}}_{7}$, could be a promising nickelate superconductor with a potential low concentration of ${V}_{\mathrm{O}}$.

Topics & Concepts