Self-doped molecular Mott insulator for bilayer high-temperature superconducting La₃Ni₂O₇

The bilayer structure of the recently discovered high-temperature superconducting nickelate La[Formula: see text]Ni[Formula: see text]O[Formula: see text] provides a new platform for investigating correlation and superconductivity. Starting from a bilayer Hubbard model, we show that there is a molecular Mott insulator limit formed by the bonding band owing to Hubbard interaction U and large inter-layer coupling. This molecular Mott insulator becomes self-doped due to electrons transferred to the anti-bonding bands at a weaker inter-layer coupling strength. The self-doped molecular Mott insulator is similar to the doped Mott insulator studied in cuprates. We propose La[Formula: see text]Ni[Formula: see text]O[Formula: see text] to be a self-doped molecular Mott insulator, whose molecular Mott limit is formed by two nearly degenerate anti-symmetric [Formula: see text] and [Formula: see text] orbitals. Partial occupation of the higher-energy symmetric [Formula: see text] orbital leads to self-doping, which may be responsible for high-temperature superconductivity in La[Formula: see text]Ni[Formula: see text]O[Formula: see text]. The effects of Hund's coupling [Formula: see text] on the low-energy spectra are also studied via exact diagonalization. The proposed low-energy theory for La[Formula: see text]Ni[Formula: see text]O[Formula: see text] is found to be valid for a wide range of U and [Formula: see text].