Spin crossover: the quantum phase transition induced by high pressure
A. I. Nesterov, S. G. Ovchinnikov
建立了凝聚态物理中高压诱导的Berry相与自旋交叉之间的关系。结果表明，几何相位具有拓扑起源，可以作为这种相变的序参量。
The relationship is established between the Berry phase and spin crossover in condensed matter physics induced by high pressure. It is shown that the geometric phase has topological origin and can be considered as the order parameter for such transition.
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Within the multielectron model of magnetic insulator with spin crossover under high pressure we have studied the mean field phase diagrams in pressure temperature plane and dynamics of a sudden excited non equilibrium spin state. We obtain the different relaxation of the magnetization, high spin/low spin occupation numbers, and the metal oxygen bond length for different values of the external pressure. We found the long living oscillations of magnetization without pressure and at small external pressure. Close to crossover pressure the smooth relaxation is accompanied with a set of sharp stron…
Deconfinement transition and dimensional crossover in the Bechgaard-Fabre salts: pressure- and temperature-dependent optical investigations
研究了有机导体（TMTSF）$_2$ PF $_6$和莫特绝缘体（TMTTF）$_2$ PF $_6$的红外响应随温度和压力的变化以及偏振方向与分子叠层平行和垂直的情况。通过在（TMTTF）$_2$ PF $_6$上施加外部压力，Mott能隙迅速减小，直到当能隙能量约为链间转移积分的两倍时发生解禁闭转变。在其去精细状态（TMTTF）下，$_2$ PF $_6$在降低温度时表现出从准一维到高维金属的交叉。对于（TMTSF）$_2$ PF $_6$，随着外部压力的增加或温度的降低，观察到这种尺寸交叉。我们定量地确定在压力-温度图的基础上，在垂直于分子堆叠的光学响应的相干程度的尺寸交叉线。
Pressure-Induced Valence Crossover and Novel Metamagnetic Behavior near the Antiferromagnetic Quantum Phase Transition of YbNi$_{3}$Ga$_{9}$
本文报道了中间价YbNi $_{3}$ Ga $_{9}$在压力和磁场作用下的电阻率、交流磁化率和X射线吸收谱的测量结果。我们揭示了一个特征的压力引起的Yb价在温度-压力相图中的交叉，和一个一阶变磁转变被发现低于$P_{\rm c}$ $\sim$ 9 GPa的系统进行压力引起的反铁磁转变。在温度-场-压力相图的基础上，讨论了在一级价转变临界点附近出现的临界价涨落，这可能是变磁行为的起源。
Quench dynamics in spin crossover induced by high pressure
本文对含时压力诱导自旋交叉的动力学进行了解析和数值研究。我们发现，准静态的压力，与时间的缓慢依赖，产生一个自旋交叉导致从高自旋（HS）的量子系统的状态过渡到低自旋（LS）。然而，在冲击波载荷下的淬火动力学更复杂。系统的最终状态取决于振幅和脉冲速度，导致HS和LS状态的混合。
Solitons in the Crossover between Band Insulator and Mott Insulator: Application to TTF-Chloranil under Pressure
基于相位哈密顿量，发现一维带状绝缘体与莫特绝缘体的交叉区存在两种类型的孤子。这两个孤子都有分数电荷，但自旋不同，分别为零和1/2。所得结果与Kanoda等对TTF-四氯对苯醌加压实验结果一致。
In solid materials, the parameters relevant to quantum effects, such as the spin quantum number, are basically determined and fixed at the chemical synthesis, which makes it challenging to control the amount of quantum correlations. We propose and demonstrate a method for active control of the classical-quantum crossover in magnetic insulators by applying external pressure. As a concrete example, we perform high-field, high-pressure measurements on CsCuCl$_3$, which has the structure of weakly-coupled spin chains. The magnetization process experiences a continuous evolution from the semi-class…
Heavy Fermion superconductor CeCu$_2$Si$_2$ under high pressure: multiprobing the valence crossover
第一个重费米子超导体CeCu $_2$ Si $_2$还没有完全揭开它的神秘面纱。在高压下，超导性被认为是由价态涨落介导的，而在环境压力下，自旋涨落最有可能充当配对粘合剂。我们对高质量的CeCu $_2$ Si $_2$单晶进行了多探针（电输运、热电势、交流比热、霍尔和能斯特效应）实验，直至$7 \text{GPa}$。可靠的电阻率数据揭示了第一次的标度行为接近假定的价态转变，并允许定位在$4.5\pm0.2 \text{GPa}$和一个稍微负的温度的临界终点。在相同的压力区域，显着的功能也已被检测到的其他物理性质，作为进一步的签名的Ce价交叉和相关的临界波动。
Crossover from impurity-induced ordered phase to uniform antiferromagnetic phase under hydrostatic pressure in the doped spin-gap system TlCu$_{1-x}$Mg$_x$Cl$_3$
用磁化强度测量方法研究了TlCuPDMATHABMM MgPDMATHABMN Cl $_3$在静水压下的磁相变.母体化合物TlCuCl $_3$是一个耦合的自旋二聚体系统，在$P_{\rm c} = 0.42$ kbar压力下，由于能隙的收缩，它经历了从带隙基态到反铁磁态的压力诱导量子相变.在常压下，本掺杂体系在$T_{\rm N}=2.5$ K下表现出杂质诱导的磁有序。随着压力的增加，$T_{\rm N}$增加。这是因为未成对自旋之间的有效交换相互作用$J_{\rm eff}$通过间隙的收缩而增强。随着压力的进一步增加，由于完整的二聚体中的三重态能隙的闭合，本系统经历了向均匀的反铁磁相的相变。在$P \simeq 1.3$ kbar时，杂质诱导的有序相转变为均匀的反铁磁相。
This work reports on the pressure dependence of the octahedra tilts and mean Fe-O bond lengths in RFeO3 (R=Nd, Sm, Eu, Gd, Tb and Dy), determined through synchrotron X-ray diffraction and Raman scattering, and their role on the pressure induced phase transition displayed by all of these compounds. For larger rare-earth cations (Nd-Sm), both anti- and in-phase octahedra tilting decrease as pressure increases, whereas the reverse behavior is observed for smaller ones (Gd-Dy). EuFeO3 stands at the borderline, as the tilts are pressure independent. For the compounds where the tilts increase with p…
We present results of magnetic susceptibility and thermal expansion measurements performed on high-quality single crystals of EuPd$_2$(Si$_{1-x}$Ge$_x$)$_2$ for 0 $\leq$ x $\leq$ 0.2 and temperatures 2 K $\leq T \leq$ 300 K. Data were taken at ambient pressure and finite He-gas pressure $p$ $\leq$ 0.5 GPa. For x = 0 and ambient pressure we observe a pronounced valence-change crossover centred around $T'_V$ $\approx$ 160 K with a non-magnetic ground state. This valence-change crossover is characterized by an extraordinarily strong pressure dependence of d$T'_V$ /d$p$ = (80 $\pm 10)$ K/GPa. We o…
We derived simple rules for the sign of superexchange interaction based on the multielectron calculations of the superexchange interaction in the transition metal oxides that are valid both below and above spin crossover under high pressure. The superexchange interaction between two cations in d$^n$ configurations is given by a sum of individual contributions related to the electron-hole virtual excitations to the different states of the d$^{n + 1}$ and d$^{n - 1}$ configurations. Using these rules, we have analyzed the sign of the superexchange interaction of a number of oxides with magnetic …
Superconductivity in strongly correlated systems is a remarkable phenomenon that attracts a huge interest. The study of this problem is relevant for materials as the high $T_c$ oxides, pnictides and heavy fermions. These systems also have in common the existence of electrons of several orbitals that coexist at a common Fermi-surface. In this paper we study the effect of pressure, chemical or applied on multi-band superconductivity. Pressure varies the atomic distances and consequently the overlap of the wave-functions in the crystal. This rearranges the electronic structure that we model inclu…
The recently discovered kagome superconductors AV3Sb5 exhibit tantalizing high-pressure phase diagrams, in which a new dome-like superconducting phase emerges under moderate pressure. However, its origin is as yet unknown. Here, we carried out the high-pressure electrical measurements up to 150 GPa, together with the high-pressure X-ray diffraction measurements and first-principles calculations on CsV3Sb5. We find the new superconducting phase to be rather robust and inherently linked to the interlayer Sb2-Sb2 interactions. The formation of Sb2-Sb2 bonds at high pressure tunes the system from …
Polaron physics and crossover transition in magnetite probed by pressure-dependent infrared spectroscopy
通过红外反射率测量研究了磁铁矿在室温下的光学性质与压力的关系，压力可达8 GPa。的光学电导率谱由一个德鲁德项，两个尖锐的声子模式，在600厘米左右的远红外带$^{-1}$，和一个明显的中红外吸收带。随着压力的增加，两个吸收带都向低频移动，声子模式以线性方式硬化。基于MIR带的形状，直流传输数据的温度依赖性，以及在光学电导率谱中的远红外带的出现，在室温下磁铁矿中的极化子耦合强度应被归类为中间。对于较低能量的声子模式的线性压力系数的突然增加发生在约6 GPa，这可能是由于不同的Fe站点之间的电荷分布的微小改变。
At ambient pressure, lithium molybdenum purple bronze (Li0.9Mo6O17) is a quasi-one dimensional solid in which the anisotropic crystal structure and the linear dispersion of the underlying bands produced by electronic correlations possibly bring about a rare experimental realization of Tomomaga-Luttinger liquid physics. It is also the sole member of the broader purple molybdenum bronzes family where a Peierls instability has not been identified at low temperatures. The present study reports a pressure-induced series of phase transitions between 0 and 12 GPa. These transitions are strongly refle…
Pressure-Induced Negative-Positive Magnetoresistance Crossover Near Metal-Insulator Transition in La_{0.8}Ag_{0.1}MnO_{3}
本研究在La_{0.8}Ag_{0.1}MnO_{3}金属-绝缘体转变附近发现高压诱导的负-正磁阻交叉，并用电子-空穴模型解释其符号变化。
Pressure-driven 4$f$ localized-itinerant crossover in heavy fermion compound CeIn$_{3}$: A first-principles many-body perspective
采用密度泛函理论和单格位动力学平均场理论相结合的方法，研究了压力下重费米子化合物CeIn $_{3}$中Ce-4 $f$价电子的定域巡游性质.详细研究了CeIn $_{3}$的电子结构演化，包括总态密度和分态密度、动量分辨谱函数和价态直方图等。在宽的压力范围内计算，其中相应的体积压缩$V/V_0 \in [0.6,1.0]$（这里$V_0$是实验晶体体积）在$T \cong 116$ K。随着压强的增加，Ce- $4f$态在费米能级附近出现两个强峰，$c$ - $f$杂化和价态涨落显著增强.此外，动能和势能的上升，而占有率，总角动量，和低能量散射率的Ce- $4f$电子相对于压力下降。这里考虑的所有物理观测值在$V/V_0 \in [0.80,0.90]$中表现出显著的扭结或波动，这可能是Ce-4 $f$定域-巡回交叉所需的指纹。
The mechanocaloric potential of spin crossover compounds
我们提出了第一个潜在的自旋交叉（SCO）的化合物被认为是一类新的巨大的机械热效应材料的评估。从文献数据的自旋交叉温度随压力的变化，我们估计几种化合物的最大可用绝热温度变化和相对较低的压力，可能需要观察这些效果。
Pressure study on the interplay between magnetic order and valence-change crossover in EuPd$_2$(Si$_{1-x}$Ge$_x$)$_2$
本文通过压力下磁化率测量研究了EuPd$_2$(Si$_{1-x}$Ge$_x$)$_2$中磁序与价态变化交叉的竞争关系，发现$x$=0.105样品在约0.06 GPa、45 K处存在一级相变的二阶临界端点，揭示了电荷、自旋和晶格自由度的强耦合效应。
Pressure-Driven Orbital Selective Insulator to Metal Transition and Spin State Crossover in Cubic CoO
采用密度泛函理论结合动力学平均场论方法研究了CoO在高压下的金属-绝缘体和自旋态转变.计算结果表明，CoO的金属-绝缘体相变是一种典型的轨道选择性Mott相变，Co 3d壳层的$t_{2g}$轨道在60 GPa附近首先变为金属态，而$e_g$轨道在170 GPa之前仍保持绝缘态.对Co 3d壳层自旋态的进一步研究表明，在中压区，Co 3d壳层的高自旋态是Mott相的主要稳定态，而从该相到完全金属态的转变是由Co $^{2+}$离子的高自旋到低自旋的转变驱动的.我们的结果与最近的运输和高压下的X射线发射实验符合得很好。
Ultrafast quantum dynamics relaxation of a photoexcited state in a strongly correlated spin crossover system LaCoO3 under a sudden perturbation is considered with the density matrix generalized master equation. The magnetization and cobalt-oxygen bond length oscillations were found. The evolution of the electronic band structure during relaxation is calculated in the framework of the LDA+GTB method.
Asymmetric phase diagram and dimensional crossover in a system of spin-1/2 dimers under applied hydrostatic pressure
研究外加静压下自旋1/2二聚体材料的磁相图演化，发现高压诱发的零场量子临界点源于层间相互作用增强导致的维度交叉，并揭示了相图中的非对称性。
Tuning the BCS-BEC crossover of electron-hole pairing with pressure
研究石墨中电子-空穴配对在静水压下的演化，发现压力可调控BCS-BEC交叉的相边界，但强耦合顶峰因面外相干长度限制而保持锁定。
Layered magnetic transition-metal thiophosphate NiPS3 has unique two-dimensional (2D) magnetic properties and electronic behavior. The electronic band structure and corresponding magnetic state are expected to sensitive to the interlayer interaction, which can be tuned by external pressure. Here, we report an insulator-metal transition accompanied with magnetism collapse during the 2D-3D crossover in structure induced by hydrostatic pressure. A two-stage phase transition from monoclinic (C2=m) to trigonal (P-31m) lattice is identified by ab initio simulation and confirmed by high-pressure XRD …
Pressure induced spin crossover in disordered α-LiFeO2
用同步辐射X射线衍射、~（57）Fe穆斯堡尔谱和金刚石压砧电阻测量等方法研究了在锂、铁离子随机分布的岩盐结构中结晶的α-LiFeO_2的结构、磁性和电输运性质。发现晶体结构至少在82 GPa下是稳定的，尽管在50 GPa以上观察到压缩性的显著变化。发现结构性质的变化与缓慢的Fe 3+从高自旋到低自旋（HS-LS）转变（S=5/2到S=1/2）相当，其开始于50 GPa，并且甚至在~100 GPa下也没有完成。HS-LS转变伴随着可观的电阻降低，直到115 GPa仍保持半导体，并且即使在约200 GPa下也不期望是金属的。观察到的压力诱导的HS-LS转变的特征不是铁氧化物在高压下的普通行为。讨论了Fe ~（3+）的最近邻和次近邻对自旋交叉特性的影响。
X-ray diffraction pressure studies at room temperature demonstrate that the spinel FeAl$_{2}$O$_{4}$ transforms to a tetragonal phase at ~18 GPa. This tetragonal phase has a highly irregular unit-cell volume versus pressure dependence up to ~45 GPa, after which a transformation to a Cmcm post-spinel phase is onset. This is attributable to pressure driven Fe-Al site inversion at room temperature, corroborated by signatures in the 57Fe Mössbauer spectroscopy pressure data. At the tetragonal to post-spinel transition, onset in the range 45-50 GPa, there is a concurrent emergence of a non-magnetic…
Field-Induced Crossover and Colossal Magnetoresistance in La(0.7)Pb(0.3)MnO(3)
在La（0.7）Pb（0.3）MnO（3）单晶的电阻率和磁化强度（M）中观察到场致交越。电阻率和M的场依赖性表明，一个小的自旋倾斜的物种与平均场的相互作用在低场（H）占主导地位，而个人的自旋和3D伊辛/海森堡模型描述的高H的行为相当不错。在铁磁转变附近，H引起的小自旋极化子的破坏伴随着大的磁阻。
Cooperative Phenomena in Spin Crossover Systems
在一个实际的多带p-d模型框架内，我们导出了一个有效的哈密顿量来描述压力下磁性Mott-Hubbard绝缘体中自旋交叉附近的交换相互作用效应.结果表明，单离子自旋交叉机制在晶场变化下不会导致热力学相变，而在T = 0时出现量子相变。结果表明，协同效应使系统的量子相变变为一级相变，并出现亚稳态。用压温相图描述了Motts介子与d 6-离子自旋交叉附近的磁化强度和高自旋布居。
Valence Transition Theory of the Pressure-Induced Dimensionality Crossover in Superconducting Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$
本文提出价态转变理论，通过Cu离子离子性离散变化与空穴转移解释SCCO压力诱导的维度交叉，为层状铜氧化物载流子密度剧增提供通用解释并给出可证伪实验测试。
We present the results of $^{75}$As nuclear magnetic resonance (NMR), nuclear quadrupole resonance (NQR), and resistivity measurements in KFe$_2$As$_2$ under pressure ($p$). The temperature dependence of the NMR shift, nuclear spin-lattice relaxation time ($T_1$) and resistivity show a crossover between a high-temperature incoherent, local-moment behavior and a low-temperature coherent behavior at a crossover temperature ($T^*$). $T^*$ is found to increase monotonically with pressure, consistent with increasing hybridization between localized $3d$ orbital-derived bands with the itinerant elect…
Spin crossover in (Mg,Fe$^{3+}$)(Si,Fe$^{3+}$)O$_3$ bridgmanite: effects of disorder, iron concentration, and temperature
含铁$^{3+}$的硼镁石是地球下地幔最丰富的矿物，铁的自旋交叉现在是一个公认的现象，尽管这种交叉的几个方面仍然不清楚。在这里，我们调查的影响，无序，铁浓度，和温度对这种交叉使用从头LDA + U $_{sc}$计算。浓度和无序的影响，解决使用完整的统计抽样耦合取代配置在超细胞包含多达80个原子。在准谐波近似的交叉振动/热效应的解决。无序的影响似乎很小，而增加铁浓度的结果在交叉压力相当大的增加。我们计算的压缩曲线的铁，铁$^{2+}$，和Fe $^{3+}$轴承的桥镁石比较以及与最新的实验测量。比较还表明，在一个封闭的系统中，Fe $^{2+}$目前在样品中可能转化为Fe $^{3+}$通过引入Mg和O空位随着压力的增加。正如铁方镁石中的自旋交叉一样，在桥镁石中的这种交叉伴随着明显的体积减小和在整个交叉压力范围内的体积模量的异常软化。这些影响随着温度的升高而显著降低。虽然[Fe $^{3+}$ ] $_{Si}$在硼镁石中的含量可能很小，但相关的弹性异常可能会影响地球下地幔径向和横向速度结构的解释。
Atomistic Description of Spin Crossover Under Pressure and its Giant Barocaloric Effect
本研究通过固态PBE+U计算揭示了典型自旋交叉配合物[FeL$_2$][BF$_4$]$_2$中压力调控转变温度的非线性机制及低频声子对巨压热效应的关键作用，并建立了精确模拟压热效应的计算协议，为发现高性能压热材料提供了工具。
High-pressure properties of MnPS$_3$ are investigated by using the hybrid functional, we report a spin-crossover pressure of 35 GPa consisting with experimental observation (30 GPa), less than half of existing report (63 GPa) using the Hubbard U correction. Interestingly, a spin-crossover induced antiferromagnetism-to-ferromagnetism transition combined with stacking-order change from monoclinic to rhombohedral are founded, and the ferromagnetism origins from the partially occupied $t_{2g}$ orbitals. Different from previous understanding, the Mott metal-insulator transition of MnPS$_3$ does not…
Magnetic-field-induced spin-crossover transition in [Mn$^{\textrm{III}}$(taa)] studied by X-ray absorption spectroscopy
研究了自旋交叉化合物[Mn $^{\textrm{III}}$（taa）]中Mn在高达37 T的脉冲强磁场中的X射线吸收近边结构（XANES）。通过对低温低自旋（LS）态施加磁场，观察到光谱的显著变化，表明磁场诱导的自旋交叉到高自旋（HS）态。在低温下，磁场依赖的光谱中的变化表现出滞后。此外，当磁场设置为零时，观察到相当大的反射分量。HS $\to$ LS跃迁的能垒由反射信号的衰减时间的温度依赖性评估。发现该跃迁的能垒为134K，明显低于以前报道的其他自旋交叉化合物的能垒。由于场致HS态的分数最多为30%，并且热动力学宏观场致相变预计发生在高于55 T的场中，所以在低至17 K的低温下观察到的场致相变可以理解为单分子水平上的局部微观相变。
Scaling and field-induced crossover of the anomalous Hall effect in SrRuO3
测量了巡游铁磁体SrRuO $_{3}$薄膜的反常霍尔效应（AHE）电阻率$ρ_{xy}$。在低温下，AHE系数$R_{s}$随$ρ_{xx}^2$变化，与侧跳和Berry相模型一致。在较高的温度下，$R_{s}$达到峰值，然后在$T_{c}$下方改变符号。我们发现，对于所有的薄膜研究$R_{s}$规模与电阻率在整个铁磁相。SrRuO $_{3}$膜具有非常低的剩余电阻率表现出场诱导的AHE在低温下的符号变化，这表明$ω_c τ$相关的交叉。
X-ray diffraction studies to ~90 GPa at room temperature show that Fe$_{2}$TiO$_{4}$ ferrous inverse spinel undergoes the following sequence of structural transitions : cubic (Fd3m) to tetragonal (I41/amd)to orthorhombic(Cmcm) to orthorhombic(Pmma),at the indicated onset transition pressures. Within the Cmcm phase, site-specific spin crossover is initiated and involves only highly distorted octahedral sites constituting ~25% of all Fe locations. This is manifest as a steeper volume decrease of dV/V0 ~ 3.5% beyond ~40 GPa and an emergent diamagnetic component discerned in 57Fe Mössbauer spectro…
Pressure-Temperature Phase Diagram of Golden SmS
测量了SmS（goldenSmS）变价相的热膨胀，绘制了压力-温度相图。所得到的相图由三条线表征。一个是将顺磁相分成两个区域的交叉线。另外两条线对应于二级Neel转变和一级Neel转变。交叉线似乎出现在一个三临界点，该点将一阶Neel转变与二阶转变分开。我们认为，在反铁磁性的边界处发生了价跳跃。
We report a detailed theoretical study of the electronic structure, spectral properties, and lattice parameters of bulk FeSe under pressure using a fully charge self-consistent implementation of the density functional theory plus dynamical mean-field theory method (DFT+DMFT). In particular, we perform a structural optimization and compute the evolution of the lattice parameters (volume, $c/a$ ratio, and the internal $z$ position of Se) and the electronic structure of the tetragonal (space group $P4/nmm$) paramagnetic FeSe. Our results for the lattice parameters are in good quantitative agreeme…
A review on magnetic field induced spin crossover in LaCoO$_{3}$ up to 600 T
本文综述了LaCoO$_{3}$在高达600 T高磁场下的自旋交叉现象，揭示了复杂相图与自旋态关联，并探讨了激子凝聚的可能性。
Crossover from Anderson- to Kondo-like behavior: Universality induced by spin-charge separation
通过精确解得到了关联基质中晶格正则化非对称Anderson杂质的热力学性质。交叉从安德森-近藤政权进行了研究，从而使接触预测标度理论。的精确解的基础上，过渡到普遍的近藤行为被证明是实现了一个渐进的分离的自旋和电荷激发的能量尺度。
Phonon-induced topological transitions and crossovers in Dirac materials
我们发现，电子-声子相互作用可以改变狄拉克绝缘体和半金属的拓扑性质，在零和非零温度。与普遍认为温度升高总是会使拓扑相不稳定相反，我们的研究结果突出了声子可能导致拓扑表面态出现在具有拓扑平凡基态的材料中的交叉温度以上的情况。
Continuous crossover between high-pressure ice phases VII and X driven by monopole screening: a model study
研究通过经典自旋-1 Blume-Capel模型探讨高压冰VII和X相之间的连续交叉机制，揭示其拓扑性质与热力学行为。
Crossover from a heavy fermion to intermediate valence state in noncentrosymmetric Yb2Ni12(P,As)7
本文报道了六方晶系化合物Yb_2Ni_（12）Pn_7（Pn = P，As）的电阻率、磁化强度、比热和部分荧光产额X射线吸收光谱（PFY-XAS）的测量结果。这些证明了减少晶胞体积时的交叉，从中间价态的Yb 2Ni 12 As 7的重费米子顺磁状态的Yb 2Ni 12 P7，其中Yb是近三价的。对Yb 2Ni 12 P7施加压力会抑制T_FL，T_FL是费米液体行为恢复的温度，这表明在压力下存在量子临界点（QCP）。然而，虽然在Yb 2Ni 12 P7的Yb价态中几乎没有变化，但在压力下，在达到接近恒定值之前，Yb 2Ni 12 As 7的Yb价态有强烈的增加。这些结果表明，在这个系统中的任何磁性QCP是很好地分离的强价涨落。的Yb 2Ni 12 As 7的价态和晶格参数的压力依赖性进行了比较，并在1 GPa，有一个异常的晶胞体积以及Yb价态的斜率的变化，表明结构和电子的变化之间的相关性。
Crossover from bias-induced to field-induced breakdowns in one-dimensional band and Mott insulators attached to electrodes
利用非平衡格林函数理论研究了一维能带和莫特绝缘体模型在外加偏压V下的非平衡态及其电流-电压特性。我们将模型连接到金属电极上，其效果被纳入自能中。在Hartree近似下，自洽地计算了电子密度的调制和来自附加长程相互作用的标量势。对于长度为L_C的带模型和莫特绝缘体模型，偏置电压引起绝缘态的击穿，击穿阈值随L_C的变化而变化。它基本上由小于相关长度$ξ=W/Δ$的L_C的偏置$V_{th}\sim Δ$确定，其中W表示带宽，而$Δ$表示能隙。对于具有$L_C\gg ξ$的系统，阈值由电场$V_{th}/L_C$决定，这与朗道-齐纳型击穿$V_{th}/L_C\propto Δ^2/W$一致。我们证明了标量势的空间依赖性是至关重要的，通过显示的情况下，没有标量势，击穿发生在$V_{th}\sim Δ$，而不管长度L_C的交叉。
The effects associated with interatomic hoppings of excitons and the excitonic Bose condensate formation in the strongly correlated spin crossover systems are considered in the framework of the effective Hamiltonian for the two-band Kanamori model. The appearance of antiferromagnetic ordering due to the exciton order is found even in the absence of interatomic exchange interaction. The spectrum of excitonic excitations is calculated at various points of the "temperature vs. crystal field" phase diagram. Outside the region of exciton ordering, the spectrum has a gap, which vanishes at the bound…
Density-induced BCS to Bose-Einstein crossover
在平均场水平上，通过引入吸引势和粒子密度，研究了零温BCS到Bose-Einstein的交叉，特别强调了粒子密度在这一交叉中所起的作用.对于三维连续介质模型，考虑了三种不同的粒子间势，而s-和d-波的解决方案进行了分析的吸引（扩展）哈伯德模型上的二维正方形格子。讨论了该模型d波解的特殊交叉行为，特别是在接近半填充的强耦合极限下，我们证明了属于不同复合玻色子的反平行自旋费米子之间的强关联，在此极限下产生了准长程反铁磁序.
Mott transition and transport crossovers in the organic compound $κ-(BEDT-TTF)_2 Cu[N(CN)_2] Cl$
我们对二维有机盐$κ$ -（BEDT-TTF）$_{2}$ Cu[N（CN）$_{2}$ ]Cl进行了面内输运测量。可变（气体）压力技术允许通过绝缘体到金属过渡的电导率的变化的详细研究。我们确定了四种不同的传输机制作为压力和温度的函数（对应于绝缘，半导体，“坏金属”，和强烈相关的费米液体行为）。在过渡区发现了明显的滞后现象，这显示了我们归因于强烈的空间不均匀性的复杂物理。远离临界区，发现良好的协议与动力学平均场计算的输运性质的数值重整化群技术。
Hydrostatic and chemical pressure driven crossover from commensurate to the incommensurate state of the Weyl semimetal Mn$_{3+x}$Sn$_{1-x}$
本研究利用μ子自旋弛豫/旋转技术和弹性中子散射，发现静水压和化学压力可驱动Weyl半金属Mn$_{3+x}$Sn$_{1-x}$从公度磁态转变为非公度磁态，并通过能带计算揭示了费米嵌套机制。
Effect of the spin crossover of local copper-oxygen states on the electronic structure of HTSC cuprates
本研究采用五带p-d模型下的GTB方法，探究不同掺杂水平下c轴单轴压力对La2-xSrxCuO4电子结构的影响，发现15.1 GPa压力下局域铜氧态自旋交叉引发电子结构突变。
Anomalous Composition-Induced Crossover in the Magnetic Properties of the Itinerant-Electron Antiferromagnet Ca{1-x}Sr{x}Co{2-y}As{2}
Ying等人[EPL 104，67005（2013）]的推断证实了在具有体心四元ThCr 2Si 2结构的Ca（1-x）Sr（x）Co（2-y）As（2）中，从小x处的共线A型反铁磁（AFM）结构（AFMI）中的c轴有序矩对准到大x处的未知AFM结构（AFMII）中的ab平面对准的组成诱导的变化。我们的主要发现是在这两个相位之间的交叉区域0.2 < x < 0.3中的异常磁性行为。在此区域，在ab平面上施加磁场H时，测量的磁化率与温度的关系chi_ab（T）表现出典型的AFM行为，在Neel温度约为65 K时出现尖点，而chi_c（T）和低温等温磁化强度M_c（H）（H沿c轴取向）则表现出极软的铁磁性质。
Induced interactions in the BCS-BEC crossover of two-dimensional Fermi gases with Rashba spin-orbit coupling
本文研究了具有Rashba自旋轨道耦合（SOC）的二维费米气体在SOC驱动的BCS-BEC交叉中对超流转变温度的Gorkov-Melik-Barkhudarov（GM）修正。在诱导相互作用的计算中，我们发现由于SOC的自旋成分混合可以诱导传统的屏蔽和额外的反屏蔽贡献，相互作用显着在强SOC制度。虽然GM校正通常会降低转变温度的估计值，但事实证明，在固定的弱相互作用下，校正效应表现出交叉行为，其中没有校正的估计值与有校正的估计值之间的比率首先随着SOC减小，然后当其进入强SOC状态时变得对SOC不敏感。我们证明了GM校正的适用性，通过比较零温度冷凝分数与最近的量子蒙特卡罗结果。
Magnetic field induced non-Fermi liquid to Fermi liquid crossover at the quantum critical point of YbCu$_{5-x}$Au$_{x}$
本文报道了近四十年来YbCu_（4.4）Au_（0.6）中μ子和$^{63}$ Cu核自旋-晶格弛豫速率$1/T_1$随温度的变化。结果表明，对于$T\to 0$ $1/T_1$发散的行为预测的自洽重整化（SCR）理论由Moriya开发的铁磁量子临界点。另一方面，静态均匀磁化率$χ_s$观察到$T^{-2/3}$和$1/T_1T\propto χ_s^2$，这是不占SCR理论的行为发散。应用磁场的$H$观察到诱导一个交叉的费米液体的行为和$T\to 0$ $1/T_1$被发现服从标度律$1/T_1(H)= 1/T_1(0)[1+(μ_BH/k_BT)^2]^{-1}$。
The pairing of interacting fermions leading to superfluidity has two limiting regimes: the Bardeen-Cooper-Schrieffer (BCS) scheme for weakly interacting degenerate fermions and the Bose-Einstein condensation (BEC) of bosonic pairs of strongly interacting fermions. While the superconductivity that emerges in most metallic systems is the BCS-like electron pairing, strongly correlated electrons with poor Fermi liquidity can condense into the unconventional BEC-like pairs. Quantum spin liquids harbor extraordinary spin correlation free from order and the superconductivity that possibly emerges by …
Here, by conducting a systematic $^{89}$Y NMR study, we explore the nature of the magnetic ground state in a newly discovered iron-based superconductor YFe$_2$Ge$_2$. An incoherent-to-coherent crossover due to the Hund's coupling induced electronic correlation is revealed below the crossover temperature $T^*\sim 75\pm15\,\mathrm{K}$. During the electronic crossover, both the Knight shift ($K$) and the bulk magnetic susceptibility ($χ$) exhibit a similar nonmonotonic temperature dependence, and a so-called Knight shift anomaly is also revealed by a careful $K$-$χ$ analysis. Such an electronic c…
Impurity-induced thermal crossover in fractional Chern insulators
研究通过玩具模型探讨杂质对分数量子反常霍尔态在有限温度范围内出现的机制，揭示杂质在分数量子反常霍尔态向整数量子反常霍尔态转变中的作用。
Conductivity of Dirac fermions with phonon induced topological crossover
本文研究了单层带隙Dirac费米子材料中的Hall电导率，包括与声子场的耦合，它不仅通过通常的自能项修正了准粒子动力学，而且直接重整化了带隙.因此，Berry曲率被修改。随着温度升高，重整化带隙的符号可以改变，并且材料可以在较高温度（T）下从带绝缘体跨越到拓扑绝缘体。谷和自旋霍尔电导率定义的有效陈数显示了丰富的相图随温度的升高。虽然自旋和谷DC霍尔电导率在升高的温度下不再量子化，但随着T增加的符号变化是拓扑交叉的明确指示。由于拓扑交叉，主要被特定谷吸收的圆偏振光的手性可以随温度而改变。
Insulator-to-metal crossover induced by local spin fluctuations in strongly correlated systems
研究了无限维极限下存在横场的简化Hubbard（SH）模型。通过微扰处理跳跃和原子极限附近的横场，得到了相应的单粒子格林函数。我们考虑杂质问题的解析解。结果表明，对于中强在位库仑相互作用$U$，该解在描述SH重粒子的光谱性质方面是非常精确的.我们发现，对于大的值的$U$的绝缘体-金属的转变发生的横场的函数。我们通过态密度、光电导率和静态电阻率的行为来分析金属相。后一个量的结果与在$Bi_2Sr_2CuO_y$实验中观察到的一致。
The spin-crossover in organometallic molecules constitutes one of the most promising routes towards the realization of molecular spintronic devices. In this article, we explore the hybridization-induced spin-crossover in metal-organic complexes. We propose a minimal many-body model that captures the essence of the spin-state switching in a generic parameter space, thus providing insight into the underlying physics. Combining the model with density functional theory (DFT), we then study the spin-crossover in isomeric structures of Ni-porphyrin (Ni-TPP). We show that metal-ligand charge transfer…
Field-induced multiple metal-insulator crossovers of correlated Dirac electrons of perovskite CaIrO$_3$
研究发现 CaIrO$_3$ 中具 Mott 临界性的关联 Dirac 电子在量子极限下发生场致连续金属–绝缘体–金属渡越，并产生 3,500% 巨磁阻。
The magnetic and magnetotransport properties of metallic 1$T$-VTe$_{2}$ single crystals were investigated at temperatures from 1.3 to 300 K and in magnetic fields up to 35 T. Upon applying a high magnetic field, it is found that the electrical resistivity displays a crossover from the logarithmic divergence of the single-impurity Kondo effect to the Fermi liquid behavior at low temperatures. The Brillouin scale of the negative magnetoresistivity above the Kondo temperature $T_{\rm{K}}$ = 12 K indicates that the Kondo features originate from intercalated V ions, with $S$ = 1/2. Both magnetic su…
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