Superexchanges and Charge Transfer in La ₃ Ni ₂ O ₇ Thin Films

Abstract The recent discovery of ambient-pressure superconductivity with a critical temperature T c exceeding 40 K in La 3 Ni 2 O 7 thin films represents a significant advancement in the field of nickelate superconductivity. Motivated by recent experimental reports, we investigate an 11-band d–p Hubbard model with tight-binding parameters derived from ab initio calculations, employing large-scale determinant quantum Monte Carlo and cellular dynamical mean-field theory. Our results show that the dominant superexchange couplings in the La 3 Ni 2 O 7 thin films are substantially weaker than those in the bulk material at 29.5 GPa. Specifically, the out-of-plane antiferromagnetic correlation between the Ni-d 3 z 2 – r 2 orbitals is reduced by approximately 27% in the film, whereas the in-plane magnetic correlations remain largely unaffected. We further evaluate the corresponding antiferromagnetic coupling constants, J ⊥ and J ∥ , within a perturbative framework. Regarding charge-transfer properties, we find that biaxial compressive strain in the films reduces the charge-transfer gap. We further resolve the orbital distribution of doped holes and electrons between the IP (Ni-d x 2 – y 2 and O-p x /p y ) and OP (Ni-d 3 z 2 – r 2 and O-p z ) orbitals, revealing a pronounced particle–hole asymmetry. These findings lay the groundwork for constructing a low-energy t – J model for La 3 Ni 2 O 7 films and provide key insights into the physical distinctions between thin-film and bulk bilayer nickelates.