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.