E. Kaneshita, A. R. Bishop
We analyze pressure effects on stripe states within a selfconsistent Hartree-Fock calculation for a model of a striped nickelates. The results show a transition induced by high pressure and predict possible new spin states. We describe characteristics in the phonon excitations at the predicted transition, based on a real-space random phase approximation.
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We report on a comprehensive study of the electronic and magnetic structure of the striped nickelate La5/3Sr1/3NiO4. The investigation is carried out using band structure calculations based on density functional theory. A magnetic structure compatible with experiment is obtained from spin-polarized calculations within the generalized gradient approximation (GGA), whereas inclusion of a local Coulomb interaction in the LDA+U framework results in a different ground state. The influence of the various interaction parameters is discussed in detail.
Nucleation processes of mixed-phase states are an intrinsic characteristic of first-order phase transitions, typically related to local symmetry breaking. Direct observation of emerging mixed-phase regions in materials showing a first-order metal-insulator transition (MIT) offers unique opportunities to uncover their driving mechanism. Using photoemission electron microscopy, we image the nanoscale formation and growth of insulating domains across the temperature-driven MIT in NdNiO3 epitaxial thin films. Heteroepitaxy is found to strongly determine the nanoscale nature of the phase transition…
We study the influence of disorder and lattice effects on the striped phase and the incommensurate spin fluctuations of the cuprates and nickelates. Starting from a phenomenological model of a discrete quantum string on a lattice with disorder, we derive the renormalisation group equations in leading order in the lattice and disorder strength. Three regimes are identified, the quantum membrane phase, the flat phase pinned by the lattice and the disorder pinned phase. We compare our results with measurements on nickelates and cuprates and find good agreement.
Ground-state properties of layered nickelates are investigated based on the orbital-degenerate Hubbard model coupled with lattice distortions, by using umerical techniques. The Néel state composed of spin S=1 ions is confirmed in the undoped limit x=0. At x=1/2, novel antiferromagnetic states, called CE- and E-type phases, are found by increasing the Hund's coupling. (3 x^2 - r^2 / 3 y^2 - r^2)-type orbital ordering is predicted to occur in a checkerboard-type charge-ordered state. At x=1/3, both Coulombic and phononic interactions are found to be important, since the former stabilizes the spi…
Using time-dependent Ginzburg-Landau theory, we study the role of amplitude and phase fluctuations in the recovery of charge and spin stripe phases in response to a pump pulse that melts the orders. For parameters relevant to the case where charge order precedes spin order thermodynamically, amplitude recovery governs the initial time scales, while phase recovery controls behavior at longer times. In addition to these intrinsic effects, there is a longer spin re-orientation time scale related to the scattering geometry that dominates the recovery of the spin phase. Coupling between the charge …
A full implementation of the $ab$ $initio$ density functional plus dynamical mean field theory (DFT+DMFT) formalism to perform total energy calculations and structural relaxations is proposed and implemented. The method is applied to the structural and metal-insulator transitions of the rare earth nickelate perovskites as a function of rare earth ion, pressure, and temperature. In contrast to previous DFT and DFT+$U$ theories, the present method accounts for the experimentally observed structure of $La$NiO$_3$ and the insulating nature of the other perovskites, and quantitatively reproduces th…
We investigate the two-dimensional t-J model at a hole doping of x = 1/8 and J/t = 0.35 with exact diagonalization. The low-energy states are uniform (not striped). We find numerous excited states with charge density wave structures, which may be interpreted as striped phases. Some of these are consistent with neutron scattering data on the cuprates and nickelates.
Electronic Correlations and Hund's Rule Coupling in Trilayer Nickelate La4Ni3O10
本文利用DFT+DMFT研究三层镍氧化物La4Ni3O10的电子关联，发现其具有轨道和层依赖性，并揭示洪特规则耦合与晶体场劈裂的竞争关系。
Experimental Progress in Ambient-Pressure Superconducting Bilayer Nickelate Films
研究环境压力下双层镍酸盐薄膜的超导特性，探讨合成方法、氧 stoichiometry、应变效应及超导性质，总结实验进展并指出待解决的问题。
Correlated electronic structure of the alternating monolayer-bilayer nickelate La$_{5}$Ni$_{3}$O$_{11}$
研究了压强下超导体La$_{5}$Ni$_{3}$O$_{11}$的关联电子结构，发现其双层结构主导低能物理特性，揭示了该家族超导体的普遍特征。
Pressure-Driven Evolution of Electronic and Magnetic Correlations in Bilayer Nickelate La3Ni2O7
本研究结合DFT、cRPA和DMFT揭示高压下La3Ni2O7的电子与磁性关联演化，发现轨道选择性演化及近藤屏蔽主导超交换导致Tc单调下降，为其超导相图提供微观解释。
Landau theory of the density wave transition in trilayer Ruddlesden-Popper nickelates
本研究针对三层Ruddlesden-Popper镍酸盐的非公度密度波转变建立朗道理论，揭示其为自旋驱动且电荷序与自旋序交织的特性，同时解释了转变温度随稀土尺寸、压强及氧同位素替换的变化规律。
Progress of ambient-pressure superconductivity in bilayer nickelate thin films
综述通过外延应变工程在La3Ni2O7薄膜中实现常压超导，并讨论相关实验表征、理论研究和超导转变温度提升。
Single-crystal structural phase diagram of stoichiometric bilayer nickelate La3Ni2O7 under hydrostatic pressure
该研究构建了静水压下化学计量双层镍酸盐La3Ni2O7的单晶压力-温度结构相图，明确其在约10 GPa发生结构相变并伴随超导出现，为镍酸盐超导微观理论提供结构基础。
Ab initio calculations predict a metal-insulator transition at zero temperature to occur in La$_4$Ni$_3$O$_8$ at moderate pressures as a result of a pressure-induced spin-state transition. The spin-state transition that is seen at 105 K at ambient pressure from a low-temperature high-spin state to a high-temperature low-spin state has been observed to be shifted to lower temperatures as pressure is applied. From our calculations we find that a smaller unit cell volume favors the metallic low-spin state, which becomes more stable at 5 GPa. Similar physics should take place in the related compou…
High-pressure crystal growth and investigation of the metal-to-metal transition of Ruddlesden-Popper trilayer nickelates La$_4$Ni$_3$O$_{10}$
本文通过浮区法在20 bar氧压下生长La$_4$Ni$_3$O$_{10}$单晶，阐明退火对结构的影响并避免铁磁杂质相，发现$P2_1/a$和Bmab两相分别在152 K和136 K发生金属-金属转变。
The dynamics of an order parameter's amplitude and phase determines the collective behaviour of novel states emerged in complex materials. Time- and momentum-resolved pump-probe spectroscopy, by virtue of its ability to measure material properties at atomic and electronic time scales and create excited states not accessible by the conventional means can decouple entangled degrees of freedom by visualizing their corresponding dynamics in the time domain. Here, combining time-resolved femotosecond optical and resonant x-ray diffraction measurements on striped La1.75Sr0.25NiO4, we reveal unforese…
Superconductivity in Ruddlesden-Popper nickelates: a review of recent progress, focusing on thin films
综述近期镍酸盐薄膜中发现常压超导性及高压力下超导性研究，探讨其对理解高温超导机制的影响。
Electronic Structure, Magnetic and Pairing Tendencies of Alternating Single-layer Bilayer Stacking Nickelate La$_5$Ni$_3$O$_{11}$ Under Pressure
本文通过密度泛函理论和随机相近似计算，研究高压下混合堆叠镍氧化物 La$_5$Ni$_3$O$_{11}$ 的电子结构与配对机制，揭示压力诱导电荷转移和单层块空穴掺杂，并预言由自旋涨落驱动的 $d_{x^2-y^2}$ 波超导配对态。
Chemical versus physical pressure effects on the structure transition of bilayer nickelates
本研究结合实验与理论，发现化学压力（小半径稀土离子替换La³⁺）会增大双层镍酸盐的正交畸变、提升结构转变临界压力，提出用大半径阳离子部分取代La³⁺或是实现常压高Tc超导的可行方向。
Pressure and doping effects on the electronic structure and magnetism of the single-layer nickelate La$_2$NiO$_4$
研究通过压力和掺杂调控单层镍酸盐La$_2$NiO$_4$的电子结构和磁性，揭示其结构、掺杂与磁性之间的相互作用。
Stabilization of Tetragonal Phase and Aluminum-Doping Effect in a Bilayer Nickelate
通过铝掺杂和退火稳定双层镍酸盐的四方相，揭示非磁性杂质对金属性和超导性的影响，为理解RP镍酸盐超导机制提供新见解。
The control of materials properties with light is a promising approach towards the realization of faster and smaller electronic devices. With phases that can be controlled via strain, pressure, chemical composition or dimensionality, nickelates are good candidates for the development of a new generation of high performance and low consumption devices. Here we analyze the photoinduced dynamics in a single crystalline NdNiO$_3$ film upon excitation across the electronic gap. Using time-resolved reflectivity and resonant x-ray diffraction, we show that the pump pulse induces an insulator-to-metal…
Theoretical study of superconductivity in freestanding infinite-layer nickelate membranes under pressure: mitigation of excess correlation enhances $T_c$
通过第一性原理构建七轨道有效模型，结合涨落交换近似，研究压力下独立无限层镍酸盐Nd$_{0.85}$Sr$_{0.15}$NiO$_2$薄膜的超导电性，发现压力通过缓解Ni原子低价态导致的过度电子关联而单调提升$T_c$。
Pressure and doping control of magnetic order and metallization in Ruddlesden-Popper La2NiO4
压力和掺杂调控Ruddlesden-Popper La2NiO4的磁序和金属化特性，揭示其磁性机制与超导性关联。
Phase diagrams and two key factors to superconductivity of Ruddlesden-Popper nickelates
本文通过密度泛函理论结合动力学平均场理论系统研究 RP 镍酸盐，发现增强的 Ni-$e_g$ 轨道准粒子权重与局部自旋涨落是超导关键因素，构建了相图并预测了新的超导候选材料。
Single crystals of the metallic Ruddlesden-Popper trilayer nickelates R$_4$Ni$_3$O$_{10}$ (R=La, Pr) were successfully grown using an optical-image floating zone furnace under oxygen pressure (pO$_2$) of 20 bar for La$_4$Ni$_3$O$_{10}$ and 140 bar for Pr$_4$Ni$_3$O$_{10}$. A combination of synchrotron and laboratory x-ray single crystal diffraction, high-resolution synchrotron x-ray powder diffraction and measurements of physical properties revealed that R$_4$Ni$_3$O$_{10}$ (R=La, Pr) crystallizes in the monoclinic $P$2$_1$/$a$ (Z=2) space group at room temperature, and that a metastable ortho…
Polar, checkerboard charge order in bilayer nickelate La3Ni2O7
研究通过高能X射线衍射揭示了双层镍酸盐La3Ni2O7在常压下的电荷有序，发现其与高温超导相竞争，揭示了极性晶体结构的形成机制。
Magnetic Correlations and Pairing Tendencies of the Hybrid Stacking Nickelate Superlattice La$_7$Ni$_5$O$_{17}$ (La$_3$Ni$_2$O$_7$/La$_4$Ni$_3$O$_{10}$) under Pressure
针对交替堆叠镍酸盐La₇Ni₅O₁₇，研究其高压下稳定高对称相的电子结构与超导配对机制，发现三层子晶格d₃z²₋ᵣ²态形成关键空穴口袋，并由面内及层间反铁磁涨落驱动s±配对，预言其Tc与双层体系相近或更高。
Single crystals of PrNiO3 were grown under an oxygen pressure of 295 bar using a unique high-pressure optical-image floating zone furnace. The crystals, with volume in excess of 1 mm3, were characterized structurally using single crystal and powder X-ray diffraction. Resistivity, specific heat, and magnetic susceptibility were measured, all of which evidenced an abrupt, first order metal-insulator transition (MIT) at ~130 K, in agreement with previous literature reports on polycrystalline specimens. Temperature-dependent single crystal diffraction was performed to investigate changes through t…
2D Weak Localization in Trilayer Ruddelsden-Popper Nickelates
本研究通过磁电导量子修正测量，揭示三层RP镍酸盐中二维弱局域化特征，表明其为准二维无序费米液体，压力可抑制该特征并可能诱导超导转变。
Correlated Electronic Structure and Density-Wave Gap in Trilayer Nickelate La4Ni3O10
研究通过高分辨率角分辨光电子能谱和从头计算，揭示三镍酸La4Ni3O10的电子结构与密度波间隙特性，为理解镍酸盐中的非常规超导性提供关键信息。
Signature of superconductivity in pressurized La4Ni3O10-x single crystals grown at ambient pressure
本文报道常压碳酸钾助熔法生长的La4Ni3O10-x单晶在77.9 GPa、约30 K出现超导迹象，为高质量镍酸盐单晶制备和高压超导研究提供新路径。
Electronic structure and magnetic correlations in trilayer nickelate superconductor La$_4$Ni$_3$O$_{10}$ under pressure
本文利用 DFT+动力学平均场理论研究了压力下三层镍酸盐 La$_4$Ni$_3$O$_{10}$ 的电子关联效应，发现 Ni $3d$ 能带存在位点和轨道依赖的重整化及 $d_{3z^2-r^2}$ 态非相干性，并指出面内自旋涨落对理解其超导电性至关重要。
Unveiling pressurized bulk superconductivity in a trilayer nickelate Pr4Ni3O10 single crystal
通过高压生长Pr4Ni3O10单晶，发现其超导临界温度达39K，揭示了镍酸盐中高温超导的通用结构与电子特征。
A-122 pnictides (A an alkaline earth element) possess striped antiferromagnetic states of orthorhombic (OR) symmetry and nonmagnetic states of tetragonal (T) symmetry. Based on total energy calculations, we show that the T = 0K pressure-driven transition from OR to T states occurs at a pressure, $P_H$, where the tetragonal enthalpy drops below the orthorhombic. The OR state remains metastable up to a higher pressure, $P_M$ > $P_H$. We find anomalies in magnetism and orthorhombicity as $P \rightarrow P_M$, and a trend towards elastic instability.
Ultrafast Magneto-Pressure Spectroscopy and Control of Correlated Phases in a Trilayer Nickelate
研究通过超快磁压光谱揭示三镍酸层中压驱动的电子不稳定性及关联相演化，发现电荷密度波相变中准粒子弛豫的临界减慢及超导相关性。
Tracing the horizon of tetragonal-to-monoclinic distortion in pressurized trilayer nickelate La4Ni3O10
研究压力下三层层镍酸盐La4Ni3O10的结构相变，发现四方到单斜转变无中间正交相，且通过XRD和DFT计算验证，揭示密度织物有序的弱无序反射。
Density-wave order enhances the phonon thermal Hall effect in a trilayer nickelate
本文报道在环境压力下三层镍酸盐La4Ni3O10中观察到有限声子热霍尔效应，密度波转变显著增强该效应，并揭示磁振子-声子杂化是主要机制。
Bulk superconductivity in quintuple-layer square-planar nickelate La6Ni5O12
该研究在五层平面正方形镍酸盐La6Ni5O12中实现了常压下的体超导电性，起始转变温度约18 K，超导体积分数约25%，为常压下研究镍酸盐超导电性提供了新的块体样品平台。
Pressure-enhanced spin-density-wave transition in double-layer nickelate $La_{3}Ni_{2}O_{7-δ}$
本研究通过$^{139}La$ NMR谱研究双层镍酸盐$La_{3}Ni_{2}O_{7-δ}$的自旋密度波转变，发现其$T_{SDW}$随压力升高而上升，与输运结果相反，为理解该体系超导与磁相互作用的关联提供了实验依据。
The material class of rare earth nickelates with high Ni$^{3+}$ oxidation state is generating continued interest due to the occurrence of a metal-insulator transition with charge order and the appearance of non-collinear magnetic phases within this insulating regime. The recent theoretical prediction for superconductivity in LaNiO$_3$ thin films has also triggered intensive research efforts. LaNiO$_3$ seems to be the only rare earth nickelate that stays metallic and paramagnetic down to lowest temperatures. So far, centimetre-sized impurity-free single crystal growth has not been reported for …
Strain mediated phase crossover in Ruddlesden Popper nickelates
本文研究了失配应变对Ruddlesden Popper镍氧化物薄膜相选择的影响，发现拉伸应变利于钙钛矿相、压缩应变稳定La3Ni2O7相，并揭示应变与Ni价态耦合导致相共存，为理解压力诱导超导中的结构缺陷问题提供了关键依据。
Bulk superconductivity up to 96 K in pressurized nickelate single crystals
研究通过高压制备镍酸盐单晶，发现其在21.6 GPa压力下最高临界温度达96 K，揭示了单斜和四方结构均可支持超导性，并建立了高压下临界温度与常温平面晶格畸变的关系。
Structural symmetry effects on the competition of density waves and superconductivity in bilayer nickelates
利用泛函重整化群研究双层镍酸盐La3Ni2O7中自旋密度波与超导电性的竞争，发现晶格对称性（正交性抑制）是调控有序态的关键，单轴应变可稳定常压超导。
Identification of the superconductivity in bilayer nickelate La$_3$Ni$_2$O$_7$ upon 100 GPa
本研究对高压下双层镍酸盐La$_3$Ni$_2$O$_7$单晶进行综合测量，发现40 GPa以上的结构转变，并在18.0 GPa下实现83 K的零电阻超导，通过Meissner效应证实其体超导性质，揭示了超导性、氧含量与结构的密切联系。
Signature of Superconductivity in Pressurized Trilayer-nickelate Pr$_4$Ni$_3$O$_{10-δ}$
本文在加压 Pr$_4$Ni$_3$O$_{10-δ}$ 多晶样品中发现超导迹象，通过压力抑制密度波并诱导结构转变，拓宽了镍酸盐超导体家族。
Multiband Metallic Ground State in Multilayered Nickelates La$_3$Ni$_2$O$_7$ and La$_4$Ni$_3$O$_{10}$ Probed by $^{139}$La-NMR at Ambient Pressure
本文通过常压 $^{139}$La-NMR 研究多层镍酸盐 La$_3$Ni$_2$O$_7$ 和 La$_4$Ni$_3$O$_{10}$，发现密度波序下的多带金属基态及费米面附近平带特征，为理解其高压高温超导提供微观依据。
Quantum phase transition driven by competing intralayer and interlayer hopping in bilayer nickelates
本研究通过调节双层镍酸盐中层内和层间跃迁比值，揭示了量子相变机制，解释了超导转变温度与晶格常数比值的相关性。
In strongly correlated materials, lattice, charge, spin and orbital degrees of freedom interact with each other, leading to emergent physical properties such as superconductivity, colossal magnetic resistance and metal-insulator transition. Quasi-2D square planar nickelates, Rn+1NinO2n+2 (R=rare earth, n=2, 3...), are of significant interest and long sought for cuprate analogue due to the 3d9 electronic configuration of Ni+, the same as the active ion Cu2+ in the high-Tc superconducting cuprates. The field has attracted intense attention since 2019 due to the discovery of superconductivity in …
Origin of the density wave instability in trilayer nickelate La$_{4}$Ni$_{3}$O$_{10}$ revealed by optical and ultrafast spectroscopy
本研究通过光学光谱和超快反射率测量揭示三层镍酸盐La₄Ni₃O₁₀中密度波不稳定性的起源，发现其为中等电子关联材料，能隙特征强于双层镍酸盐，推进了对其密度波与超导机制的理解。
High-temperature superconductivity in Nd$_{0.85}$Sr$_{0.15}$NiO$_2$ membranes under pressure
研究通过压力诱导Nd$_{0.85}$Sr$_{0.15}$NiO$_2$膜超导转变温度提升，发现线性增强机制，无饱和现象，揭示二维材料超导配对强度提升潜力。
Distinguishing Electronic Band Structure of Single-layer and Bilayer Ruddlesden-Popper Nickelates Probed by in-situ High Pressure X-ray Absorption Near-edge Spectroscopy
本研究利用原位高压XANES探究单层与双层RP-镍酸盐的电子能带结构，结合DFT计算解析光谱特征，揭示高压下BL-La327的能带演化、空穴掺杂效应及轨道选择性关联，明确两类能带与电子关联对其超导配对的关键作用。
Interstitial oxygen order and its competition with superconductivity in La$_2$PrNi$_2$O$_{7+δ}$
研究揭示了双层镍酸盐中间隙氧序与超导性的竞争关系，通过实验发现Pr掺杂和氧退火对超导性有显著影响。
Density waves in low-pressure bilayer nickelates
通过无限制Hartree-Fock计算，发现La3Ni2O7中第二个密度波转变源于电荷密度波不稳定性，导致自旋调制的双条纹自旋密度波，并建立了有序态层次，连接常压与超导高压相。
Orbital correlations in bilayer nickelates: roles of doping and interlayer coupling
本文在最小双轨道紧束缚模型中研究双层镍氧化物的轨道关联，揭示其对层间耦合、掺杂和能带细节的敏感性，并关联费米面及轨道成分变化，以解释常压下弱绝缘态的稳定机制。
Ultrafast Dynamics of Bilayer and Trilayer Nickelate Superconductors
本研究利用超快反射率测量揭示了双层与三层镍酸盐超导体在常压下超快动力学的显著差异，发现两者在相干声子模式、弛豫时间温度依赖性及电声子耦合常数上的不同，为理解微观相互作用及超导与密度波转变的相互关系奠定基础。
Charge Transfer and Zhang-Rice Singlet Bands in the Nickelate Superconductor $\mathrm{La_3Ni_2O_7}$ under Pressure
基于从头计算参数，采用量子蒙特卡洛和动力学平均场理论研究$\mathrm{La_3Ni_2O_7}$，发现其超交换耦合与铜氧化物相当，揭示了电荷转移绝缘体特性及两个低能自旋单态能带的不同关联行为，并提出有效$t-J$模型解释其超导机制。
Superconductivity of the hybrid Ruddlesden-Popper La5Ni3O11 single crystals under high pressure
本研究报告了新型混合型 Ruddlesden-Popper 镍酸盐 La5Ni3O11 在高压下的超导性，发现其在约 21 GPa 下实现 Tconset = 64 K 的最佳超导，且结构相变对超导和密度波转变无显著影响，扩展了 RP 镍酸盐超导家族。
Hund's Rule, Interorbital Hybridization, and High-$T_c$ Superconductivity in the Bilayer Nickelate
该研究用多种张量网络方法模拟双层镍酸盐双轨道模型，揭示洪特耦合与轨道间杂化的竞争协同如何决定La$_3$Ni$_2$O$_7$高压超导的升降。
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