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Ruddlesden-Popper型双层镍酸盐材料La3Ni2O7在高压（>14 GPa）下表现出约80 K的超导转变温度（Tc），引起了广泛关注[1]。该材料独特的双层结构赋予其不同于铜基超导体的电子结构特性，其超导机理具有重要的研究价值。实验发现该体系中存在电荷密度波与自旋密度波序，可能与超导态存在竞争关系，深入探究其形成机制对于理解该体系的超导本质具有重要意义。本工作结合密度泛函理论与动力学平均场理论（DFT+DMFT），在包含两个子格点Ni-eg轨道的低能有效模型基础上，引入Hartree平均场处理近邻格点间库仑相互作用，系统研究了非局域库仑相互作用对电荷有序行为与电子关联效应的影响。计算结果表明，当V ≤ Vc1 ≈ 0.46 eV时，体系保持子格点对称性，谱函数无显著变化；当V > Vc1时，子格点对称性破缺，体系进入电荷有序相，且谱函数发生明显的重构。进一步增大V至Vc2 ≈ 0.63 eV后，体系进入完全极化态，其中一个子格点近乎空，占据主要集中于另一子格点，后者接近3/4填充。本研究揭示了近邻库仑相互作用在驱动电荷不均匀分布及调控电子关联中的关键作用，为全面理解La3Ni2O7中的低能有序态提供了新的视角。The bilayer nickelate La3Ni2O7, a member of the Ruddlesden–Popper series, has recently garnered significant attention due to its superconductivity under high pressure (above 14 GPa) with a transition temperature of approximately 80 K [1]. Its unique bilayer structure results in an electronic configuration significantly distinct from those observed in cuprates and infinite-layer nickelates. Consequently, understanding its correlated electronic structure and superconducting mechanism has emerged as a topic of major scientific importance. Recent experimental observations have further identified the coexistence of charge and spin density wave orders in La3Ni2O7, suggesting a complex interplay among various competing electronic phases and superconductivity.
In this work, we investigate the charge order in La3Ni2O7 using a low-energy effective model that explicitly includes the Ni-eg orbitals. By employing a combined density functional theory and dynamical mean-field theory (DFT+DMFT) framework, we systematically explore the impact of the nearest-neighbor Coulomb interaction V on charge ordering and electronic correlation effects, with nonlocal interactions treated at the Hartree approximation level. Our computational methodology features a newly developed tensor-network impurity solver utilizing a natural-orbital basis and complex-time evolution, facilitating effcient and precise evaluations of the Green’s function on the real-frequency axis.
Our analysis reveals that for interaction strengths below a critical value (V ≤ Vc1 ≈ 0.46 eV), the system maintains sublattice symmetry, resulting in minimal changes to the spectral function. Several high-energy fine structures identified within the Hubbard bands correspond to remnants of atomic multiplet excitations, allowing extraction of effective Hubbard parameters. When V > Vc1, the sublattice symmetry breaks, and the system transitions into a charge-ordered state. Spectral features evolve systematically with increasing charge order, providing a clear benchmark to quantitatively assess the degree of charge disproportionation against experimental data. The quasiparticle weight Z exhibits a nonmonotonic behavior with increasing V , reaching a minimum near V ≈ 0.60 eV in the more populated sublattice as it approaches half-filling. Upon further increasing the interaction beyond Vc2 ≈ 0.63 eV, the system becomes fully charge polarized, characterized by one sublattice becoming nearly empty and the other approaching three-quarter filling.
These findings underscore the critical role of nonlocal Coulomb interactions in driving charge disproportionation and tuning electronic correlations, thereby offering fresh insights into the low-energy ordering phenomena of bilayer nickelates. -
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