Flat bands promoted by Hund's rule coupling in the candidate double-layer high-temperature superconductor La3Ni2O7 under high pressure

This work describes systematic strongly correlated electronic structure calculations for the candidate double-layer high-temperature superconductor La₃Ni₂O₇ under pressure. These reveal the localized-itinerant duality of Ni d_z² electrons, flat d_z² and d_x²-y² quasiparticle bands, and strong interlayer antiferromagnetic correlations due to the interplay of orbital-selective Mott, Hund, and Kondo physics. These results imply a two-component theory with possibly preformed interlayer pairing for the high-temperature superconductivity in pressurized La₃Ni₂O₇. The strange metallicity in the normal state is also explained from the quasiparticle lifetimes.