We report the low temperature magnetic properties of Nd$^{3+}$ pyrochlore $\rm Nd_2ScNbO_7$. Susceptibility and magnetization show an easy-axis moment, and heat capacity reveals a phase transition to long range order at $T_N=371(2)$ mK with a fully recovered $ΔS = R \ln(2)$, 53\% of it recovered for $T>T_N$. Elastic neutron scattering shows a long-range all-in-all-out magnetic order with low-$Q$ diffuse elastic scattering. Inelastic neutron scattering shows a low-energy flat-band, indicating a magnetic Hamiltonian similar to $\rm Nd_2Zr_2O_7$. Nuclear hyperfine excitations measured by ultra-high-resolution neutron backscattering indicates a distribution of static electronic moments below $T_N$, which may be due to B-site disorder influencing Nd crystal electric fields. Analysis of heat capacity data shows an unexpected $T$-linear or $T^{3/2}$ term which is inconsistent with conventional magnon quasiparticles, but is consistent with fractionalized spinons or gapless local spin excitations. We use legacy data to show similar behavior in $\rm Nd_2Zr_2O_7$. Comparing local static moments also reveals a suppression of the nuclear Schottky anomaly in temperature, evidencing a fraction of Nd sites with nearly zero static moment, consistent with exchange-disorder-induced random singlet formation. Taken together, these measurements suggest an unusual fluctuating magnetic ground state which mimics a spin-liquid -- but may not actually be one.
We analyze the magnon excitations in pyrochlore iridates with all-in-all-out (AIAO) antiferromagnetic order, focusing on their topological features. We identify the magnetic point group symmetries that protect the nodal-line band crossings and triple-point degeneracies that dominate the Berry curvature. We find three distinct regimes of magnon band topology, as a function of the ratio of Dzyaloshinskii-Moriya (DM) interaction to the antiferromagnetic exchange. We show how the thermal Hall response provides a unique probe of the topological magnon band structure in AIAO systems.
The nontrivial topology of quasiparticle wavefunctions can manifest themselves in the form of observable surface states. This is now well established in electronic systems, with Dirac and Weyl semimetals bringing to fore the exotic nature of these topologically protected entities. Magnons - which refer to collective excitations of localized spins - offer another sector where many of these concepts could be realized. Here, we report magneto-thermal measurements on a pyrochlore ferromagnet which is theoretically predicted to host such topological magnons. It is demonstrated that the thermoelectr…
We theoretically study the magnetic properties of pyrochlore iridate bilayer and trilayer thin films grown along the $[111]$ direction using a strong coupling approach. We find the ground state magnetic configurations on a mean field level and carry out a spin-wave analysis about them. In the trilayer case the ground state is found to be the all-in-all-out (AIAO) state, whereas the bilayer has a deformed AIAO state. For all parameters of the spin-orbit coupled Hamiltonian we study, the lowest magnon band in the trilayer case has a nonzero Chern number. In the bilayer case we also find a parame…
We investigate novel topological magnon band crossings of pyrochlore antiferromagnets with all-in-all-out (AIAO) magnetic order. By general symmetry analysis and spin-wave theory, we show that pyrochlore materials with AIAO orders can host Weyl magnons under external magnetic fields or uniaxial strains. Under a small magnetic field, the magnon bands of the pyrochlore with AIAO background can feature two opposite-charged Weyl points, which is the minimal number of Weyl points realizable in quantum materials and has not be experimentally observed so far. We further show that breathing pyrochlore…
Quasiparticle Breakdown and Spin Hamiltonian of the Frustrated Quantum Pyrochlore Yb$_2$Ti$_2$O$_7$ in Magnetic Field
阻挫烧绿石磁体Yb $_2$ Ti $_2$ O $_7$具有磁性有序的显著性质，但在布里渊区的宽区域上没有传播的磁振子。在这里，我们使用非弹性中子散射，以遵循如何频谱的演变，在垂直轴磁场。在高场，我们观察到除了色散的磁振子也是一个两个磁振子连续，它的强度增加后，减少领域和重叠的一个磁振子状态在中间领域导致强重整化的色散关系，和磁振子衰变。利用热容测量，我们发现低场区和高场区是平滑连接的，没有急剧的相变，自旋能隙随场单调增加。通过拟合到一个广泛的数据集，我们重新评估的自旋哈密顿发现占主导地位的量子交换项，我们建议负责的强烈波动和准粒子击穿效应在低场观察。
This short note documents some of the pyrochlore magnetization plateaus resulting from the arguments of Pal & Lal that were not mentioned in arxiv:1902.06475v1. These are (layered) "Kagome"-like plateaus that are commensurate with the pyrochlore lattice, including an exact wavefunction for the $\frac{m}{m_s} = \frac{5}{6}$ plateau state.
We investigate the zero- and finite-temperature properties of the bond-random $s=1/2$ Heisenberg antiferromagnet on the pyrochlore lattice by the exact diagonalization and the Hams--de Raedt methods. We find that the randomness induces the gapless quantum spin liquid (QSL) state, the random-singlet state. Implications to recent experiments on the mixed-anion pyrochlore-lattice antiferromagnet Lu$_2$Mo$_2$O$_5$N$_2$ exhibiting gapless QSL behaviors are discussed.
Thermal Hall conductivity in the frustrated pyrochlore magnet Tb2Ti2O7
在铁磁体中，自旋激发是研究得很好的磁振子。在受抑的量子磁体中，尽管自旋之间有很大的交换耦合，但长程磁序无法发展。与传统磁体中的磁振子相比，人们对它们的自旋激发知之甚少。他们是流动的还是本地的？在这里，我们表明，热霍尔电导率$κ_{xy}$提供了一个强大的探针的“量子自旋冰”烧绿石Tb $_2$ Ti $_2$ O $_7$的自旋激发。即使材料是透明的，热霍尔响应也很大。霍尔响应产生于自旋激发，具有将它们与磁振子区分开的特定特性。在低温（$T<$ 1 K）下，热导率模仿脏金属的热导率。使用霍尔角，我们构建了一个相位图，显示了如何通过磁场抑制激励。
The frustrated rare-earth pyrochlore Yb$_2$Ti$_2$O$_7$ is remarkable among magnetic materials: despite a ferromagnetically ordered ground state it exhibits a broad, nearly gapless, continuum of excitations. This broad continuum connects smoothly to the sharp one-magnon excitations expected, and indeed observed, at high magnetic fields, raising the question: how does this picture of sharp magnons break down as the field is lowered? In this paper, we consider the effects of magnon interactions in Yb$_2$Ti$_2$O$_7$, showing that their inclusion greatly extends the reach of spin-wave theory. First…
Magnetic phase diagram of the antiferromagnetic pyrochlore Gd2Ti2O7
Gd 2 Ti 2 O 7是烧绿石晶格上的高度受抑的反铁磁体，除了海森堡交换之外，自旋还通过偶极-偶极力相互作用。本文报道了在三个不同方向的外加磁场作用下对Gd_2 Ti_2 O_7单晶进行的低温比热测量。测量结果显示，强烈的各向异性行为的Gd 2 Ti 2 O 7在磁场中，尽管明显缺乏一个显着的单离子各向异性的Gd 3+。给出了H//[111]、H//[110]和H//[112]的H-T相图。结果表明，进一步的理论工作超出了一个简单的平均场模型是必要的。
Field-Driven Transitions in the Dipolar Pyrochlore Antiferromagnet Gd$_2$Ti$_2$O$_7$
本文提出了偶极耦合的钛酸钆Gd $_2$ Ti $_2$ O $_7$焦绿石体系中磁场驱动跃迁的平均场论.低温中子散射产生的相，可以被看作是一个8亚晶格反铁磁体，其中长程有序矩和涨落矩共存。我们的理论给出了实现这样一个阶段的参数区域，并预测了其他几个阶段，它们之间的过渡由磁场以及温度驱动。我们发现了几个实例{ \em本地}无序参数描述的过渡。
In an ideal classical pyrochlore antiferromagnet without perturbations, an infinite degeneracy at a ground state leads to absence of a magnetic order and spin-glass transition. Here we present Na$_3$Mn(CO$_3$)$_2$Cl as a new candidate compound where classical spins are coupled antiferromagnetically on the pyrochlore lattice, and report its structural and magnetic properties.The temperature dependences of the magnetic susceptibility and heat capacity, and the magnetization curve are consistent with those of an $S$ = 5/2 pyrochlore lattice antiferromagnet with nearest-neighbor interactions of 2 …
Valence bond crystal in a pyrochlore antiferromagnet with orbital degeneracy
本文讨论了三重轨道简并$S=1/2$磁性离子的烧绿石晶格的基态。我们推导出一个有效的自旋轨道哈密顿量，并表明轨道自由度可以调制自旋交换，消除无限自旋简并烧绿石结构的特点。由此产生的状态是自旋单重态二聚体的集合，由于它们的相对取向而具有残余简并性。后者被磁弹性相互作用提升，在自旋单态相空间中诱导，迫使四重态畸变。这种理论为在B-尖晶石MgTi $_2$ O $_4$中观察到的螺旋自旋单态模式提供了解释。
We present the results of an exact diagonalization study of the spin-1/2 Heisenberg antiferromagnet on a two-dimensional version of the pyrochlore lattice, also known as the square lattice with crossings or the checkerboard lattice. Examining the low energy spectra for systems of up to 24 spins, we find that all clusters studied have non-degenerate ground states with total spin zero, and big energy gaps to states with higher total spin. We also find a large number of non-magnetic excitations at energies within this spin gap. Spin-spin and spin-Peierls correlation functions appear to be short-r…
We investigate the ground-state properties of the nearest-neighbor $S=1$ pyrochlore Heisenberg antiferromagnet using two complementary numerical methods, density-matrix renormalization group (DMRG) and pseudofermion functional renormalization group (PFFRG). Within DMRG, we are able to reliably study clusters with up to 48 spins by keeping 20 000 SU(2) states. The investigated 32-site and 48-site clusters both show indications of a robust $C_3$ rotation symmetry breaking of the ground-state spin correlations and the 48-site cluster additionally features inversion symmetry breaking. Our PFFRG an…
Absent pinch points and emergent clusters: further neighbour interactions in the pyrochlore Heisenberg antiferromagnet
我们讨论的起源自旋相关性中子散射实验中观察到的顺磁相的一些挫折尖晶石化合物，最显着的ZnCr 2 O 4。这些相关性令人震惊，原因有二。首先，它们被解释为弱相互作用的六边形自旋簇形成的证据。其次，它们与最近邻海森堡烧绿石反铁磁体的计算结果非常不同，其中库仑相位相关产生尖锐的散射特征，称为夹点。使用大- $n$计算和蒙特卡罗模拟，我们表明，非常弱的进一步邻居交换相互作用可以占两个明显的形成集群和抑制的夹点。
Magnetic Transitions under Ultrahigh Magnetic Fields of up to 130 T in the Breathing Pyrochlore Antiferromagnet LiInCr4O8
利用脉冲磁场研究了自旋为3/2的反铁磁体LiInCr 4 O 8在高达130 T的交变磁场下的磁化过程.在90 T ~ 130 T范围内，LiInCr_4 O_8具有较强的自旋-晶格耦合，与传统的铬尖晶石氧化物相似. LiGa 0.125 In 0.875 Cr 4 O 8的磁化强度在低温下的结构和磁转变被完全抑制，在13 T以上突然增加，表明在四聚体单重基态和总自旋为1的激发态之间存在2.2 meV的自旋间隙，后者通过施加磁场而稳定。呼吸烧绿石反铁磁体是一个独特的阻挫系统，具有很强的自旋-晶格耦合和键的交替。
