Interlayer-Coupling-Driven High-Temperature Superconductivity in La3Ni2O7 under …

The newly discovered high-temperature superconductivity in La₃Ni₂O₇ under pressure has attracted a great deal of attention. The essential ingredient characterizing the electronic properties is the bilayer NiO₂ planes coupled by the interlayer bonding of 3d_{z²} orbitals through the intermediate oxygen atoms. In the strong coupling limit, the low-energy physics is described by an intralayer antiferromagnetic spin-exchange interaction J∥ between 3d_{x²-y²} orbitals and an interlayer one J⊥ between 3d_{z²} orbitals. Taking into account Hund's rule on each site and integrating out the 3d_{z²} spin degree of freedom, the system reduces to a single-orbital bilayer t-J model based on the 3d_{x²-y²} orbital. By employing the slave-boson approach, the self-consistent equations for the bonding and pairing order parameters are solved. Near the physically relevant 1/4-filling regime (doping δ=0.3∼0.5), the interlayer coupling J⊥ tunes the conventional single-layer d-wave superconducting state to the s-wave one. A strong J⊥ could enhance the interlayer superconducting order, leading to a dramatically increased Tc. Interestingly, there could exist a finite regime in which an s+id state emerges.