Motivated by the recent discovery of superconductivity in La3βNi2βO7β
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 3dx2βy2 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 x2βy2 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 dx2βy2β symmetries. Our results
highlight the role of strong multiorbital correlation effects in driving the
superconductivity of La3βNi2βO7β.Comment: 5.5+4 pages, 4+3 figures, 2 tables, updated version with supplemental
materia