Pairing Mechanism and Superconductivity in 1313 Phase La 3 Ni 2 O 7

Abstract We systematically investigate the electronic properties and superconducting mechanism of 1313 La 3 Ni 2 O 7 using density functional theory plus dynamical mean-field theory (DFT+DMFT) and random phase approximation (RPA). Our DFT+DMFT calculations reveal that the single-layer (SL) subsystem exhibits nearly insulating behavior, with the d z 2 orbital showing Mott physics, while the trilayer (TL) subsystem remains metallic. This indicates that SC primarily resides in the TL subsystem, whose Ni- e g orbitals are found to be hole-doped relative to bulk La 4 Ni 3 O 10 . Based on DFT+DMFT-derived low-energy Hamiltonian, RPA-based analysis yields an s ± -wave pairing symmetry within the TL subsystem. Importantly, we identify two key factors that contribute to the significant suppression of T c in 1313 La 3 Ni 2 O 7 compared to bulk La 4 Ni 3 O 10 . First, the hole doping in the TL subsystem leads to a decreased pairing strength. Second, the SL subsystem acts as a bridge connecting adjacent superconducting TL subsystems, thereby forming an S-N-S Josephson junction. The resulting interlayer Josephson coupling governs the phase coherence between TL subsystems and further suppresses the global T c . Combinedly, our findings suggest that the high- T c phase in the RP La 3 Ni 2 O 7 family should be attributed to the 2222 La 3 Ni 2 O 7 rather than the 1313 La 3 Ni 2 O 7 .