Evidence for charge and spin density waves in single crystals of La₃Ni₂O₇ and La₃Ni₂O₆
Evidence for charge and spin density waves in single crystals of La₃Ni₂O₇ and La₃Ni₂O₆
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Evidence for Clean d-wave Superconductivity in Samarium Nickelates
利用超快太赫兹光谱技术，对Tc为20 K的无限层钐镍氧化物薄膜进行了光学泵浦-太赫兹探测实验，测量光致电导随温度的变化。在弱激发下，光致破坏的超流密度与平衡态超流密度成正比，其随温度升高呈线性下降，符合干净极限d波配对特征。从该线性关系提取出超导能隙为2.5 meV，2Δ/kTc约等于3，表明体系处于弱耦合区间。同时，独立估算得到平均自由程与相干长度之比(l/ξ)约为1.5，进一步确认干净极限行为。这些结果证明镍氧化物超导体可实现干净超导态，并揭示其配对机制与铜氧化物高温超导体存在密切相似性。
Evidence of Spin Density Waves in La₃Ni₂O₇₋δ
Evidence of Spin Density Waves in La₃Ni₂O₇₋δ
Evidence of Spin Density Waves in La₃Ni₂O₇₋δ
The recently discovered superconductivity with critical temperature 𝑇𝑐 up to 80 K in the double-layer Nickelate La3Ni2O7−𝛿 under pressure has drawn great attention. Here, we report the positive muon spin relaxation (𝜇+SR) study of polycrystalline La3Ni2O6.92 under ambient pressure. Zero-field 𝜇+SR experiments reveal the existence of magnetic order in La3Ni2O6.92 with 𝑇𝑁=154 K. The weak transverse field 𝜇+SR measurements reveal the bulk nature of magnetism. In addition, a small quantity of oxygen deficiencies can greatly broaden the internal magnetic field distribution sensed by muons.
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 from intralayer to interlayer superconductivity in a bilayer t-J-J_{\bot} ladder
该研究以双层t-J-J⊥梯子为理论模型（受双层铜氧化物超导体和La3Ni2O7启发），其中t为面内电子跃迁、J为面内自旋交换、J⊥为层间自旋交换；作者采用密度矩阵重整化群方法，在δ=1/8–1/2的大掺杂范围内调节J⊥，并以自旋单态配对关联为主要判据，构建了双层两腿梯子的量子相图。结果表明，足够大的J⊥可在Luther-Emery液体和Luttinger液体两类母态中驱动层间超导：耦合两个Luther-Emery液体时，面内超导可经有限掺杂区间的中间电荷密度波相或直接转变为层间超导，该CDW相似由δ=1/4时两腿梯子的CDW态发展而来；耦合两个Luttinger液体时，大J⊥使体系进入层间超导，而在中间J⊥下，面内Luttinger液体特征保持稳定，层间超导则呈现幂指数Kzz_SC~1的增强准长程有序。三层梯子结果进一步表明，强J⊥可在更宽掺杂范围稳定层间超导，为理解双层铜氧化物和镍酸盐中的层间配对提供了数值依据。
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
2 条关联记录
Expanding the trilayer Ruddlesden-Popper nickelate family: Synthesis and characterization of Sm₄Ni₃O₁₀₋δ single crystals
本文报道了利用高压高温（3.25 GPa、1400 ℃）助熔剂法首次成功合成钐基三层Ruddlesden-Popper镍酸盐Sm₄Ni₃O₁₀₋δ单晶。单晶X射线衍射和粉末衍射精修表明其结构为正交Pbca空间群，沿c轴Ni−O−Ni键角约152.4°，明显偏离180°。磁化与输运测量在常压下一致观测到约180 K的密度波转变；施加高达80 GPa压力可部分抑制绝缘行为和密度波序，但未观察到超导。密度泛函理论计算显示3d_z²和3d_x²−y²轨道与其他t₂g轨道分离，是费米面的主要贡献。该结果表明Ni−O−Ni键角的严重偏离可能阻碍超导出现，新合成的Sm₄Ni₃O₁₀₋δ为研究RP镍酸盐基础物理提供了独特平台。