Dirac spin liquids represent a class of highly-entangled quantum phases in two dimensional Mott insulators, featuring exotic properties such as critical correlation functions and absence of well-defined low energy quasi-particles. Existing numerical works suggest that the spin-orbital $SU(4)$ symmetric Kugel-Khomskii model of Mott insulators on the honeycomb lattice realizes a Dirac spin-orbital liquid, described at low energy by $(2+1)d$ quantum electrodynamics (QED$_3$) with $N_f=8$ Dirac fermions. We generalize methods previously developed for $SU(2)$ spin systems to analyze the symmetry properties and stability of the Dirac spin-orbital liquid. We conclude that the standard Dirac state in the $SU(4)$ honeycomb system, based on a simple parton mean-field ansatz, is intrinsically unstable at low energy due to the existence of a monopole perturbation that is allowed by physical symmetries and relevant under renormalization group flow. We propose two plausible alternative scenarios compatible with existing numerics. In the first scenario, we propose an alternative $U(1)$ Dirac spin-orbital liquid, which is similar to the standard one except for its monopole symmetry quantum numbers. This alternative $U(1)$ state represents a stable gapless phase. In the second scenario, we start from the standard $U(1)$ Dirac liquid and Higgs the $U(1)$ gauge symmetry down to $\mathbb{Z}_4$. The resulting $\mathbb{Z}_4$ Dirac spin-orbital liquid is stable. We also discuss the continuous quantum phase transitions from the $\mathbb{Z}_4$ Dirac liquids to conventional symmetry-breaking orders, described by the QED$_3$ theory with $N_f=8$ supplemented with a critical charge-$4$ Higgs field. We discuss possible ways to distinguish these scenarios in numerics. We also extend previous calculations of the quantum anomalies of QED$_3$ and match with generalized lattice Lieb-Schultz-Mattis constraints.
Relaxor ferroelectric behavior and intrinsic magnetodielectric behavior near room temperature in Li2Ni2Mo3O12, a compound with distorted honeycomb and spin-chains
保持当前的兴趣，以确定材料的内在磁介电行为在室温附近，并与新的热释电电流异常，我们报告的温度和磁场依赖的行为的复介电常数和热释电电流的氧化物，Li 2Ni 2 Mo 3 O 12，含有磁性离子（扭曲）蜂窝和链的安排和有序磁低于8 K。介电数据揭示了在160-240 K范围内存在弛豫铁电行为，并且在该温度范围内也存在相应的拉曼模式异常。热电流行为也与这种解释一致，有趣的是，热电流峰值温度与极化温度相关。~ 7 Li NMR研究表明，该化合物存在晶体学无序，这种无序是导致弛豫铁电性质的局部电场随机性的重要原因。另一个值得注意的观察结果是，在300 K下，施加磁场时，介电常数显著降低至约-2.4%，其幅度随温度略微变化。小的损耗因子值验证在室温下的磁介电效应的固有行为。
Ground state and low-temperature magnetism of the quasi-two-dimensional honeycomb compound InCu$_{2/3}$V$_{1/3}$O$_3$
我们报告了一个组合的$^{115}$在NQR，$^{51}$ V NMR和$μ$ SR光谱研究的低温磁性的InCu $_{2/3}$ V $_{1/3}$ O $_3$，准二维（2D）化合物，包括在自旋扇区的反铁磁耦合自旋$S=1/2$蜂窝晶格与铜$^{2+}$离子。尽管大量的实验和理论的努力，这种材料的基态是没有最终确定。特别是，在不同的磁测量中表现为异常的两个特征温度约为$\sim 40$ K和$\sim 20$ K，本文对此进行了有争议的讨论。对实验数据的综合分析与交换常数的理论计算相结合，使我们能够在39 K以下识别出“中间”准二维静态自旋态。这种自旋状态的特点是交错磁化与温度演化，同意的2D XY模型的预测。我们观察到，该状态在15 K时逐渐转变为完全发展的3D反铁磁Néel状态。我们归因于这样一个扩展的准2D静态制度的蜂窝状平面的有效的磁去耦由于层间交换相互作用，抑制长距离自旋-自旋相关的平面之间的强烈挫折。有趣的是，我们发现的拓扑Berezinsky-Kosterlitz-无相变的迹象在准二维静态的蜂窝自旋1/2平面的InCu $_{2/3}$ V $_{1/3}$ O $_3$。
Kadanoff Center for Theoretical Physics & Enrico Fermi Institute, University of Chicago（芝加哥大学卡达诺夫理论物理中心与恩里科·费米研究所）；School of Mathematics, University of Birmingham（伯明翰大学数学学院）；Mani L. Bhaumik Institute for Theoretical Physics, Department of Physics and Astronomy, University of California, Los Angeles（加州大学洛杉矶分校曼尼·L·巴乌米克理论物理研究所与物理天文学系）
Observation of a phase transition within the domain walls of ferromagnetic Co3Sn2S2
Co $_3$ Sn $_2$ S $_2$的铁磁相被广泛认为是一种拓扑Weyl半金属，从传输和光谱探针的Berry曲率的动量空间单极的证据。由于能带结构对磁序高度敏感，人们的注意力集中在远低于居里温度的磁化强度、磁化率和输运测量中的异常，导致人们猜测“隐藏”相与铁磁性共存。在这里，我们报告空间分辨测量克尔效应显微镜，确定这一阶段。我们发现，异常符合深最小的畴壁（DW）的流动性，表明DW传播的两个制度之间的交叉。我们证明，这种交叉是一个二维相变内DW，其中的磁化织构从连续旋转到单向变化发生变化的表现。我们建议，这种2D过渡的存在，深内的铁磁状态的散装是一个巨大的品质因数的结果，磁晶各向异性独特的这种化合物。这项工作拓宽了传统的二元分类的DWs到布洛赫和Néel墙的视野，并提出了新的策略，操纵域壁和它们的作用，在电子和自旋输运。
