Electron correlations and superconductivity in La3Ni2 O7 under pressure tuning

Motivated by the recent discovery of superconductivity in La3Ni2O7 under pressure, we discuss the basic ingredients of a model that captures its microscopic physics under pressure tuning. We anchor our description in terms of the spectroscopic evidence of strong correlations in this system. In a bilayer Hubbard model including the Ni 3d x2-y2 and z2 orbitals, we show the ground state of the model crosses over from a low-spin S=1/2 state to a high-spin S=3/2 state. In the high-spin state, the two x2-y2 and the bonding z2 orbitals are all close to half-filling, which promotes a strong orbital selectivity in a broad crossover regime of the phase diagram pertinent to the system. Based on these results, we construct an effective multiorbital t-J model to describe the superconductivity of the system, and find the leading pairing channel to be an intraorbital spin singlet with a competition between the extended s-wave and dx2-y2 symmetries. Our results highlight the role of strong multiorbital correlation effects in driving the superconductivity of La3Ni2O7.