Interlayer-Coupling-Driven High-Temperature Superconductivity in La 3 Ni 2 O 7 under Pressure

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 3dz2 orbitals through the intermediate oxygen atoms. In the strong coupling limit, the low-energy physics is described by an intralayer antiferromagnetic spin-exchange interaction Jk between 3dx2-y2 orbitals and an interlayer one J perpendicular to between 3dz2 orbitals. Taking into account Hund's rule on each site and integrating out the 3dz2 spin degree of freedom, the system reduces to a singleorbital bilayer t-J model based on the 3dx2-y2 orbital. By employing the slave-boson approach, the selfconsistent equations for the bonding and pairing order parameters are solved. Near the physically relevant 4-filling regime (doping delta 1/4 0.3 similar to 0.5), the interlayer coupling J perpendicular to tunes the conventional single-layer d-wave superconducting state to the s-wave one. A strong J perpendicular to 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.