Interplay of two Eg orbitals in superconducting La3Ni2O7 under pressure

The discovery of high-T-c superconductivity (SC) in La3Ni2O7 (LNO) has aroused a great deal of interest. Previously, it was proposed that the Ni-3d(z2) orbital is crucial to realize the high-T-c SC in LNO. The preformed Cooper pairs therein acquire coherence via hybridization with the 3d(x2-y2) orbital to form the SC. However, we held a different viewpoint that the interlayer pairing s-wave SC is induced by the 3d(x2-y2) orbital, driven by the strong interlayer superexchange interaction. To include effects from both E-g orbitals, we establish a two-orbital bilayer t-J model. Our calculations reveal that due to the no-double-occupancy constraint, the 3d(x2-y2) band and the 3d(z2) bonding band are flattened by a factor of about 2 and 10, respectively, which is consistent with recent angle-resolved photoemission spectroscopy measurements. Consequently, a high-temperature SC can be hardly induced in the 3d(z2) orbital due to the difficulty to develop phase coherence. However, it can be easily achieved by the 3d(x2-y2) orbital under realistic interaction strength. With electron doping, the 3d(z2)-band gradually dives below the Fermi level, but T-c continues to enhance, suggesting that it is not necessary for the high-T-c SC in LNO. With hole doping, T-c initially drops and then rises, accompanied by the crossover from the BCS to BEC-type superconducting transitions.