Electronic correlations and superconducting instability in La3Ni2O7 under high pressure

Motivated by the report of superconductivity in bilayer ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ at high pressure, we examine the interacting electrons in this system. First-principles many-body theory is utilized to study the normal-state electronic properties. Below 100 K, a multiorbital non-Fermi-liquid state resulting from a loss of Ni-ligand coherence within a flat-band-dominated low-energy landscape is uncovered. The incoherent low-temperature Fermi surface displays strong mixing between $\mathrm{Ni}\text{\ensuremath{-}}{d}_{{z}^{2}}$ and $\mathrm{Ni}\text{\ensuremath{-}}{d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ orbital character. In a model Hamiltonian picture, spin fluctuations originating mostly from the $\mathrm{Ni}\text{\ensuremath{-}}{d}_{{z}^{2}}$ orbital give rise to strong tendencies towards a superconducting instability with a ${B}_{1g}$ or ${B}_{2g}$ order parameter. The dramatic enhancement of ${T}_{\mathrm{c}}$ in pressurized ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ is due to stronger $\mathrm{Ni}\text{\ensuremath{-}}{d}_{{z}^{2}}$ correlations compared to those in the infinite-layer nickelates.