Electronic and magnetic excitations in La3Ni2O7

Abstract The striking discovery of high-temperature superconductivity (HTSC) of 80 K in a bilayer nickelate La₃Ni₂O₇ under a moderately high pressure of about 14 GPa ignited a new wave of studying HTSC in nickelates. The properties of the parental phase at ambient pressure may contain key information on basic interactions therein and bosons that may mediate pairing giving birth to superconductivity. Moreover, the bilayer structure of La₃Ni₂O₇ may suggest a distinct minimal model in comparison to cuprate superconductors. Here using X-ray absorption spectroscopy and resonant inelastic X-ray scattering, we studied La₃Ni₂O₇ at ambient pressure, and found that Ni 3dx²y², Ni 3dz², and ligand oxygen 2p orbitals dominate the low-energy physics with a small charge-transfer energy. Remarkably, well-defined optical-like magnetic excitations were found to soften into a quasi-static spin-density-wave ordering, evidencing the strong electronic correlations and rich magnetic properties. Based on a Heisenberg spin model, we found that the inter-layer effective magnetic superexchange interaction is much larger than the intra-layer ones, and proposed viable magnetic structures. Our results highlight that the strong bonding of Ni 3dz² orbitals within the bilayer structure induces novel electronic and magnetic excitations setting the stage for further exploration of La₃Ni₂O₇ superconductor.