Electronic structures and multi-orbital models of La3Ni2O7 thin films at ambient pressure

The recent discovery of superconductivity with a transition temperature T c exceeding 40 K in La 3 Ni 2 O 7 and (La, Pr) 3 Ni 2 O 7 thin films at ambient pressure marks a significant breakthrough in the field of nickelate superconductors. Using density functional theory (DFT), we propose a double-stacked two-orbital effective model for La 3 Ni 2 O 7 thin film based on the Ni − e g orbitals. Our analysis of the Fermi surface reveals three electron pockets ( α ,α ^ ,β α , α ′ , β ) and two hole pockets ( γ ,γ ^ γ , γ ′ ), where the additional α ^ α ′ and γ ^ γ ′ pockets arise from inter-stack interactions. Furthermore, we introduce a high-energy model that incorporates O− p orbitals to facilitate future studies. Calculations of spin susceptibility within the random phase approximation (RPA) indicate that magnetic correlations are enhanced by nesting of the γ pocket, which is predominantly derived from the Ni -d_z² − d z 2 orbital. Our results provide a theoretical foundation for understanding the electronic and magnetic properties of La 3 Ni 2 O 7 thin films.