Interplay of two Eg orbitals in superconducting La3Ni2O7 under pressure

Abstract

The discovery of high-Tc superconductivity (SC) in La3Ni2O7 (LNO) has aroused a great deal of interest. Previously, it was proposed that the Ni-3dz2 orbital is crucial to realize the high-Tc SC in LNO. The preformed Cooper pairs therein acquire coherence via hybridization with the 3dx2−y2 orbital to form the SC. However, we held a different viewpoint that the interlayer pairing s-wave SC is induced by the 3dx2−y2 orbital, driven by the strong interlayer superexchange interaction. To include effects from both Eg orbitals, we establish a two-orbital bilayer t−J model. Our calculations reveal that due to the no-double-occupancy constraint, the 3dx2−y2 band and the 3dz2 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 3dz2 orbital due to the difficulty to develop phase coherence. However, it can be easily achieved by the 3dx2−y2 orbital under realistic interaction strength. With electron doping, the 3dz2-band gradually dives below the Fermi level, but Tc continues to enhance, suggesting that it is not necessary for the high-Tc SC in LNO. With hole doping, Tc initially drops and then rises, accompanied by the crossover from the BCS to BEC-type superconducting transitions.

Source-reported materials — not catalogue approval

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