Formation of unusual oxygen vacancy chains in nickelate La3Ni2O7

Abstract

The recently reported nickelate La3Ni2O7 under pressure provides a new platform for exploring unconventional superconductivity. The oxygen vacancies (VO's) are inevitably introduced during the sample preparation, as confirmed by experimental observations. While it is believed the VO's could play a key role in influencing the superconductivity of La3Ni2O7, their basic structural and electronic properties remain to be clarified. Here, combining the cluster expansion method and first-principles calculations, we successfully identify eight intermediate ground states of La3Ni2O7–x with variable x. Contrary to the general assumption of a random distribution, surprisingly, we find the VO's eventually form exotic one-dimensional chain structures along the in-plane direction in La3Ni2O7–x. These recently discovered VO chains significantly change the electronic properties with redistributed electrons and altered orbital interactions. The dz2 orbitals of Ni atoms adjacent to the VO chain become fully occupied, with a decreased proportion around the Fermi level (EF). Importantly, a flat dx2−y2 orbital that emerges above EF enhances the transition dipole moment, leading to a prominent peak in optical conductivity perpendicular to the chain, which is ready to be detected experimentally. Furthermore, Wannier downfolding analysis demonstrates significant variations in orbital interactions caused by the VO chains, particularly the sign changes in intrabilayer dz2 hopping. Our study provides the benchmark structures of La3Ni2O7–x and develops a deeper insight into the fundamental electronic and optical properties of La3Ni2O7–x.

Source-reported materials — not catalogue approval

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