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

The bilayer structure of recently discovered high-temperature superconducting nickelates La3Ni2O7 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 interlayer coupling. This molecular Mott insulator becomes self-doped due to electrons transferred to the antibonding bands at a weaker interlayer coupling strength. The self-doped molecular Mott insulator is similar to the doped Mott insulator studied in cuprates. We propose La3Ni2O7 to be a self-doped molecular Mott insulator, whose molecular Mott limit is formed by two nearly degenerate antisymmetric dx²-y² and dz² orbitals. Partial occupation of higher energy symmetric dx²-y² orbital leads to self-doping, which may be responsible for high-temperature superconductivity in La3Ni2O7. The effects of Hund’s coupling JH on the low-energy spectra are also studied via exact diagonalization. The proposed low-energy theory for La3Ni2O7 is found to be valid in a wide range of U and JH.