Electronic structure, self-doping, and superconducting instability in the alternating single-layer trilayer stacking nickelates La3Ni2O7

Abstract

Motivated by the recently proposed alternating single-layer trilayer stacking structure for the nickelate La3⁢Ni2⁢O7, we comprehensively study this system using ab initio and random-phase approximation techniques. Our analysis unveils similarities between this novel La3⁢Ni2⁢O7 structure and other Ruddlesden-Popper nickelate superconductors, such as a similar charge-transfer gap value and orbital-selective behavior of the 𝑒𝑔 orbitals. Pressure primarily increases the bandwidths of the Ni 𝑒𝑔 bands, suggesting an enhancement of the itinerant properties of those 𝑒𝑔 states. By changing the cell volume ratio 𝑉/𝑉0 from 0.9 to 1.10, we found that the bilayer structure in La3⁢Ni2⁢O7 always has lower energy than the single-layer trilayer stacking La3⁢Ni2⁢O7. In addition, we observe a “self-doping” effect (compared to the average 1.5 electrons per 𝑒𝑔 orbital per site of the entire structure) from the trilayer to the single-layer sublattices and this effect will be enhanced by overall electron doping. Moreover, we find a leading 𝑑𝑥2−𝑦2-wave pairing state that is restricted to the single layer. Because the effective coupling between the single layers is very weak, due to the nonsuperconducting trilayer in-between, this suggests that the superconducting transition temperature 𝑇𝑐 in this structure should be much lower than in the bilayer structure.