Electronic and magnetic excitations in La3Ni2O7

High-temperature superconductivity was discovered in the pressurized nickelate La3Ni2O7 which has a unique bilayer structure and mixed valence state of nickel. The properties at ambient pressure contain crucial information of the fundamental interactions and bosons mediating superconducting pairing. Here, using X-ray absorption spectroscopy and resonant inelastic X-ray scattering, we identified that Ni 3 d_x²-y² , Ni 3 d_z² , and ligand oxygen 2p orbitals dominate the low-energy physics with a small charge-transfer energy. Well-defined optical-like magnetic excitations soften into quasi-static spin-density-wave ordering, evidencing the strong electronic correlation and rich magnetic properties. Based on an effective Heisenberg spin model, we extract a much stronger inter-layer effective magnetic superexchange than the intra-layer ones and propose two viable magnetic structures. Our findings emphasize that the Ni 3 d_z² orbital bonding within the bilayer induces novel electronic and magnetic excitations, setting the stage for further exploration of La3Ni2O7 superconductor. It was recently found that a certain nickelate compound, La3Ni2O7, at moderately high pressures has a superconducting phase that persists to above liquid nitrogen temperatures. Here, by studying the parent phase at ambient pressure, Chen et al uncover rich magnetic properties and show the vital role of the strong bonding of the inter-layer Ni orbitals in the magnetic and electronic excitations.