Oxygen deficiency mechanism of La3Ni2O7−δ under pressure

Abstract

The recent discovery of superconductivity in pressurized bilayer nickelate La₃Ni₂O₇ has triggered tremendous research interest. However, the experimentally observed oxygen deficiency implies that obtaining perfect stoichiometric single crystals is still challenging. The influence of oxygen deficiency on physical properties remains unexplained. Here, we construct a chemical potential phase diagram to characterize the stability of La₃Ni₂O₇. The narrow stable region explains the difficulty of synthesizing pure samples. First, oxygen defect studies reveal that the interlayer apical oxygen vacancy has the highest defect concentrations and is responsible for oxygen deficiency. Second, unfolding band structures show as the oxygen-deficient variant increases, Ni \(3d_{\;z^{2}}\) bands shift toward a lower energy position under the Fermi level at Γ point, which is adverse to the metallization of Ni \(3d_{\;z^{2}}\) bands. Third, high-pressure calculations indicate that oxygen vacancy would destroy the hybridization of interlayer Ni \(3d_{\;z^{2}}\) orbitals, and the larger the oxygen deficiency, the higher the pressure needed to metalize the Ni \(3d_{\;z^{2}}\) bands. Thus, the oxygen deficiency would suppress the emergence of superconductivity in La₃Ni₂O_7−δ. Our results elucidate the mechanism of oxygen deficiency for superconductivity in La₃Ni₂O_7−δ and provide instructive guidance to the experimental research.