Incommensurate spin-fluctuations and competing pairing symmetries in La3Ni2O7

Abstract: The recent discovery of superconductivity in the bilayer Ruddlesden-Popper nickelate La3Ni2O7 under high pressure has generated much interest in the superconducting pairing mechanism of nickelates. Despite extensive theoretical work, the superconducting pairing symmetry in La3Ni2O7 remains unresolved, with conflicting results even for identical methods. This inconsistency has obscured the pairing mechanism and raised questions about the validity of simplified models. We argue that different superconducting states in La3Ni2O7 are in close competition and highly sensitive to the choice of interaction parameters as well as pressure-induced changes in the electronic structure. Our study uses a multi-orbital Hubbard model, incorporating all Ni 3d and O 2p states. We analyze the superconducting pairing mechanism of La3Ni2O7 within the random phase approximation and find a transition between d-wave and sign-changing s-wave pairing states as a function of pressure and interaction parameters, which is driven by spin-fluctuations with different wave vectors. These spin-fluctuations with incommensurate wave vectors cooperatively stabilize a superconducting order parameter with dx2-y2 symmetry for realistic model parameters. Simultaneously, their competition may be responsible for the absence of magnetic order in La3Ni2O7, demonstrating that magnetic frustration and superconducting pairing can arise from the same set of incommensurate spin-fluctuations.