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-classical realm to the highly-quantum regime with increasing pressure. Based on the idea of "squashing" the spin chains onto a plane, we characterize the change in the quantum correlations by the change in the value of the local spin quantum number of an effective two-dimensional model. This opens a way to access the tunable classical-quantum crossover of two-dimensional spin systems by using alternative systems of coupled-chain compounds.
The temperature-dependent evolution pattern of 5f electrons helps to elucidate the long-standing itinerant-localized dual nature in plutonium-based compounds. In this work, we investigate the correlated electronic states of PuIn3 dependence on temperature by using a combination of the density functional theory and the dynamical mean-field theory. Not only the experimental photoemission spectroscopy is correctly reproduced, but also a possible hidden 5f itinerant-localized crossover is identified. Moreover, it is found that the quasiparticle multiplets from the many-body transitions gradually e…
Crossover from charge density wave stabilized antiferromagnetism to superconductivity in Nd$_{1-x}$La$_x$NiC$_2$ compounds
本文研究了用La离子逐步取代Nd，从电荷密度波反铁磁体NdNiC $_2$到非中心对称超导体LaNiC $_2$的路径。通过结构、磁性、输运、磁电阻和比热测量探索了物理性质的演变。随着La取代Nd，Peierls温度逐渐降低，其临界浓度为$x_c$ = 0.38，符合BCS平均场化学压力关系。只要保持电荷密度波，反铁磁基态对掺杂仍然是稳健的，尽管Néel温度降低，但显示出快速和急剧的磁性转变。一旦CDW被完全抑制，Nd $_{1-x}$ La $_x$ NiC $_2$系列的中间化合物显示出与AFM转变和自旋无序增加相关的特征逐渐软化的症状。在反铁磁转变被压低到零温度后，La离子的进一步掺入导致超导电性的出现。讨论了Nd $_{1-x}$ La $_x$ NiC $_2$中可能的量子临界点。
Itinerant-localized crossover and orbital dependent correlations for 4$f$ electrons in cerium-based ternary 122 compounds
采用密度泛函理论结合单格位动力学平均场论，系统地研究了铈基三元122化合物Ce $M_{2}$ Si $_{2}$（其中$M =$ Ru，Rh，Pd，Ag）的电子结构.计算了动量分辨谱函数、总态密度和4个$f$分态密度、自能函数和价态涨落。所得结果与已有的实验数据吻合较好。有人建议，在增加原子序数从Ru到Ag，4 $f$电子应该变得越来越本地化。当$M$从Pd转变为Ag时，可能出现由化学压力驱动的4个$f$电子的巡回局域交叉。特别地，根据4个$f$自能函数的低频行为，我们在CeAg $_{2}$ Si $_{2}$中发现了一个轨道选择性的4个$f$绝缘态，这是完全出乎意料的.
We study LiFeP, LiFeAs and NaFeAs in their paramagnetic metallic phase including dynamical electronic correlations within a density functional theory + slave-spin mean-field framework. The three compounds are found to lie next to the crossover between a normal and a Hund's metal, where a region of enhanced electronic compressibility that may boost superconductivity is systematically present in this type of systems. We find that LiFeP lies in the normal metallic regime, LiFeAs at the crossover, and NaFeAs is in the Hund's metal regime, which possibly explains the different experimental trends f…
Crossover from Single-Ion to Coherent Non-Fermi Liquid Behavior in Ce$_{1-x}$La$_x$Ni$_9$Ge$_4$
我们报告了在整个化学计量范围内对化合物Ce ${}_{1-x}$ La ${}_x$ Ni ${}_9$ Ge ${}_4$在不同浓度下的比热和磁阻研究。我们的数据揭示了Ce浓度在$x = 0.1$和0.95之间的单离子缩放。此外，CeNi ${}_9$ Ge ${}_4$在$T=0.08$ K下具有有史以来最大的电子比热$Δc/T \approx$ 5.5 J $\rm K^{-2}mol^{-1}$，这是在铈f电子晶格系统中发现的。在掺杂的样品中，$Δc/T$在3 K和50 mK之间的温度范围内以非费米液体（nFl）行为的典型值递增，而$ρ$在30 K附近表现出Kondo样的最小值，然后是单离子局部nFl行为。与此相反，CeNi ${}_9$ Ge ${}_4$在低于300 mK时在$Δc/T$中出现，并在1.5 K时的电阻率曲线中显示出明显的最大值，表明相干重费米子基态。这些性质使得化合物Ce ${}_{1-x}$ La ${}_x$ Ni ${}_9$ Ge ${}_4$成为费米液体和nFl物理之间的边界上的独特系统。
We present the influences of electronic and magnetic correlations and doping evolution on the groundstate properties of recently discovered superconductor Ba$_{2}$CuO$_{4-δ}$ by utilizing the Kotliar-Ruckenstein slave boson method. Starting with an effective two-orbital Hubbard model (Scalapino {\it et al.} Phys. Rev. {\bf B 99}, 224515 (2019)), we demonstrate that with increasing doping concentration, the paramagnetic (PM) system evolves from two-band character to single-band ones around the electron filling n=2.5, with the band nature of the $d_{3z^{2}-r^{2}}$ and $d_{x^{2}-y^{2}}$ orbitals …
Universität Würzburg（维尔茨堡大学）；CINECA National Supercomputing Center（CINECA国家超级计算中心）；LPEM, ESPCI Paris, PSL Research University, CNRS, Sorbonne Université（LPEM，巴黎高等物理化工学院，PSL研究大学，法国国家科学研究中心，索邦大学）
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$_3$
The stranglehold of low temperatures on fascinating quantum phenomena in one-dimensional quantum magnets has been challenged recently by the discovery of anomalous spin transport at high temperatures. Whereas both regimes have been investigated separately, no study has attempted to reconcile them. For instance, the paradigmatic quantum Heisenberg spin-$1/2$ chain falls at low temperature within the Tomonaga-Luttinger liquid framework, while its high-temperature dynamics is superdiffusive and relates to the Kardar-Parisi-Zhang universality class in $1+1$ dimensions. This Letter aims at reconcil…
Energy-dependent crossover from anisotropic to isotropic magnetic dispersion in lightly-doped La1.96Sr0.04CuO4
对轻掺杂La $_{1.96}$ Sr $_{0.04}$ CuO $_{4}$进行了非弹性中子散射实验，发现低温下存在对角非公度自旋关联.我们以前报道过，这种晶体，与一个单一的斜方晶域，表现出“沙漏”分散在低能量[物理评论快报。101，197001（2008）]。在本文中，我们详细调查的能量演化的磁激发高达65毫电子伏。结果发现，在低能量的各向异性激发，仅沿自旋调制方向分散，交叉到各向同性，圆锥形的分散体，类似于在母体化合物La $_2$ CuO $_{4}$的自旋波。从两重到完全对称的变化跨越沙漏的腰部再现的行为首先在欠掺杂的YBa $_2$ Cu $_3$ O $_{6+x}$的研究中确定。我们讨论了这些结果的意义。
Spin glassiness and power law scaling in a quasi-triangular spin-1/2 compound
我们提出了两类层状自旋S=1/2反铁磁准三角晶格材料的磁性数据：$Cu_{2(1-x)}Zn_{2x}(OH)_3NO_3$（$0 < x < 0.65$）和它的长链有机衍生物$Cu_{2(1-x)}Zn_{2x}(OH)_3(C_7H_{15}COO)\cdot mH_2O$（$0 < x < 0.29$），其中非磁性Zn取代Cu同构。结果发现，长链化合物，即使在一个干净的系统中，在没有稀释，$x\!=\!0$，显示自旋玻璃行为，证明了DC和AC的磁化率，并通过随时间变化的磁化测量。一个引人注目的特点是观察到的两个连续的幂律政权之间的急剧交叉在冻结温度以上的直流磁化率。比热数据与未插层化合物中的常规相变和长链化合物中的玻璃态行为一致。
Magneto-elastic distortions are commonly detected across magnetic long-range ordering (LRO) transitions. In principle, they are also induced by the magnetic short-range ordering (SRO) that precedes a LRO transition, which contains information about short-range correlations and energetics that are essential for understanding how LRO is established. However these distortions are difficult to resolve because the associated atomic displacements are exceedingly small and do not break symmetry. Here we demonstrate high-multipole nonlinear optical polarimetry as a sensitive and mode selective probe o…
Fragile three-dimensionality in the quasi-one-dimensional cuprate PrBa_2Cu_4O_8
在这篇文章中，我们报告的实验实现的尺寸交叉现象的链状化合物PrBa $_2$ Cu $_4$ O $_8$使用温度，高磁场和无序作为独立的调谐参数。在较纯的PrBa $_2$ Cu $_4$ O $_8$晶体中，在低温下形成高度各向异性的三维费米液态。然而，这种金属状态对无序非常敏感，并且快速地定位。我们表明，通过相关的能量尺度的定量比较，这种金属/绝缘体交叉发生时，链内的散射率超过链间跳跃率（S），即一旦载流子成为局限于一个单一的导电元素。
