Electron correlations and superconductivity in La3Ni2O7 under pressure tuning*

We address the recently discovered high temperature superconductivity in La3Ni2O7, by anchoring our description via the spectroscopic evidence of strong correlations in the system. We discuss the electron correlation effects in a bilayer Hubbard model including the Ni 3d x2-y2 and z2 orbitals, and show that the ground state of the model crosses over from a low-spin S=1/2 state to a high-spin S=3/2 state. We find that the system exhibits strong orbital selectivity over a wide crossover regime, as the consequence of proximity to an orbital-selective Mott phase. Based on these results, we construct an effective multiorbital t-J model to describe the superconductivity, and find the leading pairing channel to be an intraorbital spin singlet with a competition between extended s-wave and dx2-y2 symmetries. Our results provide a theoretical understanding of the spectroscopic experimental data and the high-temperature superconductivity.