The newly discovered Ruddlesden-Popper (RP)-type bilayer lanthanum nickel oxide \mathrmLa_3Ni_2O_7 has emerged as a pivotal candidate in high-temperature superconductivity research, following copper-based and iron-based superconductors. Its superconducting transition temperature reaching 80 K under high pressure has sparked intense interest, yet the correlated electronic properties under ambient pressure—an essential foundation for elucidating the superconducting mechanism—remain insufficiently understood. To address this gap, we systematically investigate the electronic structure and correlation effects of ambient-pressure \mathrmLa_3Ni_2O_7 using a combined theoretical approach.

First, we constructed an effective 11-orbital tight-binding model via density functional theory (DFT) calculations (implemented in VASP) with the projector augmented-wave (PAW) method, generalized gradient approximation (GGA-PBE) for exchange-correlation energy, and a cutoff energy of 600 eV. The model includes Ni’s \mathrmd_z^2 and \mathrmd_x^2-y^2 orbitals (dominant near the Fermi level) and seven O-p orbitals (including in-plane \mathrmp_x/\mathrmp_y, interlayer apical \mathrmp_z, and outer interlayer \mathrmp_z'/\mathrmp_z'' orbitals), derived via Wannier90 orbital projection. Notably, the model reflects the charge-transfer nature of transition metal oxides, with indirect d-d hopping mediated by oxygen p orbitals instead of direct d-d transitions.

We then employed cluster dynamical mean-field theory (CDMFT) to account for strong electronic correlations, a key limitation of conventional DFT in describing 3d transition metal oxides. The CDMFT calculations utilized the continuous-time quantum Monte Carlo (CTQMC) hybridization expansion (CTHYB) impurity solver (implemented in TRIQS-CTHYB) with \beta=25, Coulomb repulsion U=7\ \texteV, Hund’s coupling J_\mathrmH=0.7\ \texteV, and double-counting corrections E_\mathrmdc^z=11.87\ \texteV (for \mathrmd_z^2) and E_\mathrmdc^x=9.85\ \texteV (for \mathrmd_x^2-y^2).

Our results reveal three core physical findings:

1) Fermi liquid behavior and orbital-selective interlayer correlations: Ambient-pressure \mathrmLa_3Ni_2O_7 exhibits a Fermi liquid phase, evidenced by the Matsubara self-energy \varSigma(\mathrmi\omega) whose imaginary part vanishes near zero frequency. The orbital representation of \varSigma(\mathrmi\omega) uncovers a non-zero interlayer self-energy for the \mathrmd_z^2 orbital (mediated by oxygen p orbitals), while the interlayer self-energy of \mathrmd_x^2-y^2 is nearly zero—indicating pronounced interlayer correlations in \mathrmd_z^2 orbitals that are absent in \mathrmd_x^2-y^2 orbitals (a result of higher-order Hund’s coupling-mediated processes and lower electron density in \mathrmd_x^2-y^2).

2) Distinct electronic structure of \mathrmd_z^2 bonding states: The local impurity Matsubara Green’s function G_\textloc(\mathrmi\omega) in the bonding-antibonding representation shows that the \mathrmd_z^2 bonding state is uniquely occupied and located below the Fermi level (evidenced by a large positive real part at zero frequency), differing sharply from other bonding/antibonding states. The imaginary part of G_\textloc(\mathrmi\omega) further indicates that the \mathrmd_x^2-y^2 antibonding state contributes the largest spectral weight near the Fermi level, followed by \mathrmd_z^2 antibonding, \mathrmd_x^2-y^2 bonding, and \mathrmd_z^2 bonding states.

3) Fermi surface topology and valley-like DOS near E_\mathrmF: Analytic continuation of the Matsubara self-energy to real frequencies reveals a valley-like structure in the orbital-resolved density of states (DOS) near the Fermi level, consistent with experimental observations of weak insulating behavior at ambient pressure. The upper peak of this valley (\approx+0.07\ \texteV) originates from quasiparticle dispersion near the Γ point (dominated by \mathrmd_z^2 orbitals), while the lower peak (\approx-0.07\ \texteV) arises from flat bands along the Γ-X direction (dominated by \mathrmd_x^2-y^2 orbitals). The Fermi surface features α (electron-like, centered at Γ) and β (hole-like, centered at M) pockets, with the γ pocket absent—an observation that aligns well with angle-resolved photoemission spectroscopy (ARPES) measurements. Additionally, the real-frequency spectral function A(k, E) shows well-defined quasiparticle dispersion near E_\mathrmF and incoherent Hubbard bands at \omega\approx\pm5\ \texteV, while the interlayer apical oxygen \mathrmp_z orbitals contribute non-negligible weight near E_\mathrmF, confirming charge-transfer characteristics.

Finally, we investigated the effect of Coulomb repulsion U (with fixed J_\mathrmH=0.7\ \texteV) on interlayer correlations: increasing U enhances orbital renormalization (evidenced by the inverse renormalization factor Z^-1=1-\dfrac\partial \textIm\Sigma (\mathrmi\omega) \partial \mathrmi\omega \Big|_\mathrmi\omega \to 0) while reducing the magnitude of the \mathrmd_z^2 interlayer self-energy (attributed to increased pd charge-transfer energy and reduced hopping probability).

This study provides a comprehensive characterization of the correlated electronic properties of ambient-pressure \mathrmLa_3\mathrmNi_2\mathrmO_7, highlighting the critical role of \mathrmd_z^2 interlayer correlations and Fermi surface topology in governing its ground state. These findings deepen our understanding of the material’s ambient-pressure behavior. Future work will explore symmetry-breaking phases (e.g., density waves, magnetism) using DMFT-based approaches, further advancing our understanding of nickel-based superconductors.