Oxygen vacancy induced site-selective Mott transition in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>LaNiO</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:math>

Abstract

While defects such as oxygen vacancies in correlated materials can modify their electronic properties dramatically, understanding the microscopic origin of electronic correlations in materials with defects has been elusive. Lanthanum nickelate with oxygen vacancies, ${\mathrm{LaNiO}}_{3\ensuremath{-}x}$, exhibits the metal-to-insulator transition as the oxygen vacancy level $x$ increases from the stoichiometric ${\mathrm{LaNiO}}_{3}$. In particular, ${\mathrm{LaNiO}}_{2.5}$ exhibits a paramagnetic insulating phase, also stabilizing an antiferromagnetic state below ${T}_{N}\ensuremath{\simeq}152\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. Here, we study the electronic structure and energetics of ${\mathrm{LaNiO}}_{3\ensuremath{-}x}$ using first principles. We find that ${\mathrm{LaNiO}}_{2.5}$ exhibits a ``site-selective'' paramagnetic Mott insulating state at $T\ensuremath{\simeq}290\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ as obtained using density functional theory plus dynamical mean field theory ($\mathrm{DFT}+\mathrm{DMFT}$). The Ni octahedron site develops a Mott insulating state with strong correlations as the Ni ${e}_{g}$ orbital is half-filled while the Ni square-planar site with apical oxygen vacancies becomes a band insulator. Our oxygen vacancy results cannot be explained by the pure change of the Ni oxidation state alone within the rigid band-shift approximation. Our $\mathrm{DFT}+\mathrm{DMFT}$ density of states explains that the peak splitting of unoccupied states in ${\mathrm{LaNiO}}_{3\ensuremath{-}x}$ measured by the experimental x-ray absorption spectra originates from two nonequivalent Ni ions in the vacancy-ordered structure.

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