Self-doped Molecular Mott Insulator for Bilayer High-Temperature Superconducting La3Ni2O7

Abstract

The bilayer structure of recently discovered high-temperature superconducting nickelates La${}_3$Ni${}_2$O${}_7$ 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 La${}_3$Ni${}_2$O${}_7$ to be a self-doped molecular Mott insulator, whose molecular Mott limit is formed by two nearly degenerate antisymmetric $d_{x^2-y^2}$ and $d_{z^2}$ orbitals. Partial occupation of higher energy symmetric $d_{x^2-y^2}$ orbital leads to self-doping, which may be responsible for high-temperature superconductivity in La${}_3$Ni${}_2$O${}_7$. The effects of Hund's coupling $J_H$ on the low-energy spectra are also studied via exact diagonalization. The proposed low-energy theory for La${}_3$Ni${}_2$O${}_7$ is found to be valid in a wide range of $U$ and $J_H$.

8+5 pages, 5+1 figures