用热膨胀和磁致伸缩研究CeRu $_2$ Si $_2$在绝对零度附近的新量子临界性

非常规量子临界性作为过渡金属化合物、重费米子系统和有机导体的新共同语言出现

Unconventional quantum criticality emerging as a new common language of transition-metal compounds, heavy-fermion systems, and organic conductors

我们分析和概述了几种不同的非常规量子临界。非常规性的一个起源是接近一阶转变。一阶跃迁和连续跃迁之间的边界由量子三临界点（QTCP）描述。与传统的量子临界点（QCP）相比，其特征之一是伴随的序参量发散和均匀涨落。几个令人困惑的非费米液体属性被称为占的情况下，YbRh 2Si 2，CeRu 2Si 2和β-YbAlB 4。另一个更戏剧性的非常规性出现在这种情况下的拓扑转变，如金属-绝缘体和Lifshitz转变。这个边界，边际量子临界点（MQCP），属于一个前所未有的普适类发散均匀波动在零温度。MQCP具有一个独特的特征，即破密性和拓扑转换的组合特征。V2-xCrxO 3和有机导体kappa-（ET）2Cu[N（CN）2]Cl的实验结果支持了理论结果。识别拓扑转变也揭示了非费米液体如何在金属中作为一个相出现。该理论还解释了ZrZn 2中变磁性转变的临界性，将其解释为Lifshitz转变和相关效应的相互作用。我们在这些例子中讨论了共同的基础物理。

Pristine quantum criticality in a Kondo semimetal

The observation of quantum criticality in diverse classes of strongly correlated electron systems has been instrumental in establishing ordering principles, discovering new phases, and identifying the relevant degrees of freedom and interactions. At focus so far have been insulators and metals. Semimetals, which are of great current interest as candidate phases with nontrivial topology, are much less explored in experiments. Here we study the Kondo semimetal CeRu$_4$Sn$_6$ by magnetic susceptibility, specific heat, and inelastic neutron scattering experiments. The power-law divergence of the m…

Field-induced phase transitions of the Kitaev material $α$-RuCl$_3$ probed by thermal expansion and magnetostriction

High-resolution thermal expansion and magnetostriction measurements were performed on single crystals of $α$-RuCl$_3$ in magnetic fields applied parallel to the Ru-Ru bonds. The length changes were measured in the direction perpendicular to the honeycomb planes. Our data show clear thermodynamic characteristics for the field-induced phase transition at the critical field $μ_0H_{c1} = 7.8(2)$ T where the antiferromagnetic zigzag order is suppressed. At higher fields, a kink in the magnetostriction coefficient signals an additional phase transition around $μ_0H_{c2} \approx 11$ T. The extracted …

Quantum criticality in the spin-${1}/{2}$ Heisenberg chain system copper pyrazine dinitrate

The magnetic insulator copper pyrazine dinitrate comprises antiferromagnetic spin-1/2 chains that are well described by the exactly solvable one-dimensional Heisenberg model, providing a unique opportunity for a quantitative comparison between theory and experiment. Here, we investigate its thermodynamic properties with a particular focus on the field-induced quantum phase transition. Thermal expansion, magnetostriction, specific heat, magnetization and magnetocaloric measurements are found to be in excellent agreement with predictions from exact Bethe-Ansatz results as well as from effective …

热膨胀法研究Sr_3Ru_2O_7的电子向列性及其与量子临界性的关系

Electronic nematicity and its relation to quantum criticality in Sr_3Ru_2O_7 studied by thermal expansion

我们报告的高分辨率测量的面内热膨胀各向异性在附近的电子在Sr $_3$ Ru $_2$ O $_7$下降到非常低的温度和在不同的磁场取向。对于沿c方向施加的场，在α相发现了明显的二阶相变，临界行为与二维伊辛普适类相容（尽管这不是完全确定的）。在一个稍微倾斜的磁场中的测量揭示了一个破碎的四重面内旋转对称性，不仅在α相内，而且向稍大的领域延伸。我们还分析了普遍的标度行为预期的一个变磁量子临界点，这是实现外的磁区。磁致伸缩的轮廓表明量子临界性和相变之间的关系。

重费米子铁氧铌酸盐Ce（Ru $_{1-x}$ Fe $_x$）PO的铁磁量子临界点

Ferromagnetic Quantum Critical Point in Heavy-Fermion Iron Oxypnictide Ce(Ru$_{1-x}$Fe$_x$)PO

我们对Ce（Ru_{1-x} Fe_{x}）PO进行了~（31）P-NMR测量，以研究铁磁（FM）量子临界性，因为具有二维结构的重费米子（HF）铁磁体CeRuPO通过等价Fe取代Ru而转变为HF顺磁体。我们发现Ce（Ru_{0.15} Fe_{0.85}）PO在低至\sim 0.3 K时表现出临界涨落，同时Fe取代对居里温度和有序矩的持续抑制。这些实验结果表明，FM量子临界点（QCP）的存在下，在x \sim 0.86，这是一个罕见的例子巡回铁磁体。此外，我们还指出Ce（Ru_{0.15} Fe_{0.85}）PO的临界行为与YbRh_{2} Si_{2}中的临界行为有相似之处，其中讨论了$f$电子的局域临界性.发现Ce（Ru_{1-x} Fe_{x}）PO是研究HF化合物FM量子临界性的新体系。

Uniaxial stress tuning of geometrical frustration in a Kondo lattice

Hexagonal CeRhSn with paramagnetic $4f$ moments on a distorted Kagome lattice displays zero-field quantum critical behavior related to geometrical frustration. We report high-resolution thermal expansion and magnetostriction measurements under multiextreme conditions such as uniaxial stress up to 200 MPa, temperatures down to 0.1 K and magnetic fields up to 10 T. Under uniaxial stress along the $a$-direction, quantum criticality disappears and a complex magnetic phase diagram arises with a sequence of phases below 1.2 K and fields between 0 and 3 T ($\parallel a$). Since the Kondo coupling inc…

反铁磁体CeRh $_2$ Si $_2$的高场变磁性

High-field metamagnetism in the antiferromagnet CeRh$_2$Si$_2$

本文研究了反铁磁体CeRh $_2$ Si $_2$在高达50特斯拉的脉冲磁场中的转矩、磁致伸缩和输运以及在高达13特斯拉的静磁场中的热膨胀。从这些测量中推导出CeRh $_2$ Si $_2$的磁场-温度相图，其中磁场沿易磁化轴$\mathbf{c}$施加。二级相变温度$T_{N}$和一级相变温度$T_{1,2}$（零场时分别为~36 K和26 K）随电场的增加而降低。场致反铁磁-顺磁边界线$H_c$在1.5 K时为26 T，从低温时的一阶变为高温时的二阶。磁场-温度相图被发现是由（至少）三个不同的反铁磁相。它们被一阶谱线$H_{1,2}$和$H_{2,3}$分开，前者对应于H=0时的$T_{1,2}$，后者在1.5 K时等于25.5 T。的最大值的$T^2$ -系数$A$的电阻率观察在发病的高场极化制度，这被解释为一个增强的有效质量的签名在场诱导的量子不稳定性。将CeRh $_2$ Si $_2$中$A$系数的磁场依赖性与其压力依赖性进行了比较，并与原型重费米子系统CeRu $_2$ Si $_2$中$A$的场依赖性进行了比较。

Kitaev候选材料Na$_2$Co$_2$TeO$_6$中的量子临界端点特征

Signatures of a Quantum Critical Endpoint in the Kitaev Candidate Na$_2$Co$_2$TeO$_6$

本研究针对Kitaev候选材料Na₂Co₂TeO₆，通过高分辨率电容膨胀测量法发现量子临界端点特征，证实该材料的量子临界端点可同时由磁场和压力调控，拓展了展现变磁性量子临界性的材料范畴。

用复合磁电方法探测临界自旋涨落：以Kitaev自旋液体候选材料Na$_3$Co$_2$SbO$_6$为例

Probing critical spin fluctuations with a composite magnetoelectric method: A case study on a Kitaev spin liquid candidate Na$_3$Co$_2$SbO$_6$

本研究提出一种高灵敏度复合磁电方法探测量子磁体临界自旋涨落，在Kitaev自旋液体候选材料Na₃Co₂SbO₆中观测到三临界点处信号发散，发现磁场方向可作为新调谐参数用于量子临界点搜索。