High-TC superconductivity in La3Ni2O7 based on the bilayer two-orbital t-J model

The recently discovered high-T_c superconductor La₃Ni₂O₇ has sparked renewed interest in unconventional superconductivity. Here we study superconductivity in pressurized La₃Ni₂O₇ based on a bilayer two-orbital t−J model, using the renormalized mean-field theory. Our results reveal a robust s^±-wave pairing driven by the inter-layer d_z² magnetic coupling, which exhibits a transition temperature within the same order of magnitude as the experimentally observed T_c ~ 80 K. We establish a comprehensive superconducting phase diagram in the doping plane. Notably, the La₃Ni₂O₇ under pressure is found to be situated roughly in the optimal doping regime of the phase diagram. When the d_x²−y² orbital becomes close to half-filling, d-wave and d + is pairing can emerge from the system. We discuss the interplay between Fermi surface topology and different pairing symmetries. The stability of the s^±-wave pairing against Hund's coupling and other magnetic exchange couplings is discussed.