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Spin-charge-orbital order in nickelate superconductors

High-pressure studies have revealed superconductivity in La4⁢Ni3⁢O10, sparking interest in its ambient-pressure properties and the underlying electronic correlations. Motivated by experimental observations of an incommensurate spin-density wave (SDW) at ambient pressure, we investigate the SDW characteristics and possible superconductivity in La4⁢Ni3⁢O10 using a multiorbital random-phase approximation (RPA). Starting with a 12-orbital tight-binding model derived from density functional theory (DFT) calculations, we include Hubbard interactions to explore the interplay between electronic correlations and magnetic instabilities. Our analysis reveals a stripe-like SDW with a wave vector 𝐐≈(±0.7⁢𝜋,0), suggesting a possible density wave instability in agreement with experiments. This configuration is driven by nesting between the 𝛼1 pocket, primarily contributed by the outer-layer Ni 𝑑𝑧2 orbitals, and the 𝛽1 pocket, contributed by both the 𝑑𝑧2 and 𝑑𝑥2−𝑦2 orbitals of the outer layer. It exhibits interlayer antiferromagnetic ordering between the top and bottom NiO layers, with the magnetic moment of the middle layer being nearly zero. We demonstrate that the Hund coupling 𝐽𝐻 is the primary driver of the observed SDW and determine the specific criterion: 𝐽𝐻>0.16⁢𝑈. Building upon our findings on the SDW mechanism, we further demonstrate that hole doping (𝛿=−0.4) enhances Fermi surface nesting, leading to the emergence of a superconducting state with a gap structure similar to that of the high-pressure phase.

本研究成功合成了高质量的长程有序杂化1313型La₃Ni₂O₇单晶（交替单层-三层结构），并对其物理性质进行了系统表征。在常压下，该材料呈现典型的半导体行为，并在170 K处出现明显的电阻率、磁化率和比热异常。¹³⁹La核磁共振谱明确证实该异常源于自旋密度波（SDW）相变。高压电输运测量表明，施加压力可以诱导金属化，但在高达65 GPa的压力下未观察到超导电性。这些发现将杂化1313型La₃Ni₂O₇确立为Ruddlesden-Popper镍酸盐家族中具有独特SDW转变的新成员，为研究杂化镍酸盐中晶体结构、电子序和超导电性之间的相互作用提供了新的平台。

采用密度泛函理论结合团簇动力学平均场方法，本文研究了双层Ruddlesden-Popper镍酸盐，发现其物理性质主要受由3z²−r²轨道单电子形成的层间“动力学单态”支配，这些单态与巡游的x²−y²平面轨道发生杂化。该杂化对静水压与面内压应变的响应截然不同：应变增强层间关联，导致轨道选择性单态配对莫特机制，而静水压主要提升面内巡游性。这一差异解释了块材与应变薄膜在角分辨光电子能谱和输运测量中的实验分歧。理论框架将此低能态视为动力学单态与巡游轨道的杂化体系，为后续理解超导电性提供了新思路。

Stabilizing and tuning superconductivity in La₃Ni₂O₇−δ films: Oxygen recycling protocol reveals hole-doping analogue

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After several decades of studies of high-temperature superconductivity, there is no compelling theory for the mechanism yet; however, the spin fluctua…