Evidence of Spin Density Waves in La₃Ni₂O₇−δ
Evidence of Spin Density Waves in La₃Ni₂O₇−δ
Knowledge
Evidence of universal spectral collapse at a marginal dynamical regime
该研究提出，强关联材料中非相干电子态并非源于无序或材料特定机制，而是由竞争涨落导致的自生动力学无序所产生。在这一边际动力学区域中，电子动力学与时间依赖散射自然耦合，导出谱函数形式ρ(z)=exp(-z²/4)D_ν(z)，其中z为标度能量，D_ν为抛物柱面函数，且ν=-1/2固定。通过对铜氧化物Nd₂₋ₓCeₓCuO₄和Bi₂Sr₂CaCu₂O₈₊δ、Kagome金属CsCr₃Sb₅以及双层镍酸盐La₃Ni₂O₇的角分辨光电子能谱（ARPES）能量分布曲线进行独立标度后，所有数据集坍塌至同一普适曲线，仅振幅与能量标度因材料而异。该光谱坍塌表明低能区域中晶格几何、能带结构与化学成分等微观细节不再相关，呈现固定点般的动力学行为。这一结果建立了跨多种强关联材料的连续主导型ARPES谱的统一定量框架。
Evolution of structure and density wave order in La₃Ni₂O₇−δ single crystals at ambient pressure
The recent discovery of high-temperature superconductivity in bilayer nickelate La3Ni2O7−δ single crystals under high pressure has sparked significant interest in the correlated electronic physics and unconventional pairing mechanisms within Ruddlesden-Popper phase nickelates, where the oxygen content plays a crucial role in both structure and superconductivity. Here we report the evolution of the structure and density wave order in La3Ni2O7−δ single crystals at ambient pressure under various oxygen annealing conditions. Structural analysis reveals that with the increase of annealing oxygen pressure, La3Ni2O7−δ undergoes a structural phase transition from an orthorhombic to a tetragonal phase. Magnetic torque measurements indicate that the density wave order, present in the orthorhombic phase, vanishes upon transition to the tetragonal structure, accompanied by an abrupt change in carrier concentration. A phase diagram illustrating the dependence of both the crystal structure and density wave order on the annealing oxygen pressure is mapped. Our findings suggest a promising pathway for studying the interplay between structure, density wave order, and superconductivity in bulk nickel-based materials.
Evolution of the Superfluid Density in Infinite-Layer Nickelates
该论文通过互感法系统测量了无限层镍基超导体Nd1-xSrxNiO2在掺杂超导穹顶内的超流密度。研究发现，超流刚度较弱，且与超导转变温度Tc呈近似平方根关系。同时，观察到Nd的4f磁矩与超流之间存在强烈的相互作用，导致低温下超流密度显著被抑制，其效应远超简单的顺磁解释，暗示了磁有序与超导相的耦合。这些结果表明，超导相位涨落在限制Tc中起重要作用，并揭示了稀土磁性离子与超流之间意想不到的强耦合。
Exact diagonalization
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Experimental evidence of Tc enhancement above 50 K and diode and paramagnetic-Meissner effects, in Nickelate films on highly reduced SrTiO₃
本研究在高度还原且导电的SrTiO₃衬底上制备了缺氧镍酸盐薄膜，通过迈斯纳效应和输运测量观察到超导起始温度达到50–70 K，并在20–25 K实现零电阻，表明超导存在于薄膜中的岛状区域。在约48 K处出现巨大的顺磁迈斯纳效应峰，进一步支持了该温度附近的超导转变。此外，还观测到非互易、无磁滞的超导二极管效应，其极性可完全偏振并反转。薄膜由多种Ruddlesden-Popper相（包括无限层相）混合构成。这些增强的超导特性归因于缺氧薄膜与高度还原的SrTiO₃衬底的协同作用。
Experimental Progress in Ambient-Pressure Superconducting Bilayer Nickelate Films
双层Ruddlesden-Popper镍酸盐在高压下呈现近80 K的超导电性，而近期通过外延应变在常压下稳定了RA₃Ni₂O₇（RA为稀土或碱土元素）超导薄膜，使输运、光谱、显微及器件测量成为可能。本综述总结了常压超导双层镍酸盐薄膜的实验进展，涵盖合成路线、氧计量比、衬底诱导应变、正常态输运、超导性质、掺杂相图以及动量分辨电子结构。当前未解决的关键问题包括：纯相超薄膜的可重复性、两步超导转变的微观起源、氧缺陷和衬底掺杂的作用、Ni 3dz₂衍生γ带的位置以及配对对称性。文章最后指出，未来需建立晶体结构、轨道重建与超导电性之间更定量的联系，以深入理解此类非常规高温超导体系。
fermi surface nesting
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fermi surface reconstruction
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fermi surface topology
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