The paper shows that strong local electron correlations change which superconducting gap theories predict for pressurized La3Ni2O7. Simple weak-coupling calculations often put this nickelate near a tie between a sign-changing s-wave (called s±) and several d-wave states. When the authors include correlation effects in a specific way, the balance is decisively shifted toward the s± state.

The researchers started from a four-orbital model of La3Ni2O7 taken from prior density functional work (the Xia et al. Wannier Hamiltonian). They combined single-site two-orbital dynamical mean-field theory (DMFT) — a method that captures strong, local electron correlations — with a random-phase approximation (RPA) for spin fluctuations. The central technical step was to replace the usual “bare” particle–hole bubble G0G0 used in RPA by a bubble built from the DMFT Green’s functions (GDMFTGDMFT), while keeping the same onsite Slater–Kanamori interaction vertices (a standard form of local electron–electron interaction). The DMFT calculations used UDMFT = 4.0 eV and JDMFT = 0.5 eV at T ≈ 116 K and a filling of three electrons per bilayer unit cell. The low-frequency DMFT self-energy gives orbital-dependent quasiparticle weights Zz ≈ 0.47 for the d3z2−r2 orbital and Zx ≈ 0.63 for the dx2−y2 orbital, showing stronger renormalization in the d3z2−r2 sector.

The outcome is a clear reversal of the pairing hierarchy. In the ordinary (bare) RPA benchmark the leading instability is in the B2g channel, corresponding to a dxy-like gap. After dressing the particle–hole bubble with the DMFT self-energy, the leading instability becomes an A1g sign-changing s± state. The dx2−y2 (B1g) channel is subleading and the original dxy instability is strongly suppressed. The authors trace this change to orbital-selective renormalization: the heavy renormalization of the d3z2−r2 orbital reduces the scattering processes that involve the γ Fermi-pocket and that had favoured the dxy state in bare RPA. At the same time, distributed inter-pocket scattering processes that favour s± survive the renormalization.