Recent theoretical studies have found quantum spin liquid states with spinon Fermi surfaces upon the application of a magnetic field on a gapped state with topological order. We investigate the thermal Hall conductivity across this transition, describing how the quantized thermal Hall conductivity of the gapped state changes to an unquantized thermal Hall conductivity in the gapless spinon Fermi surface state. We consider two cases, both of potential experimental interest: the state with non-Abelian Ising topological order on the honeycomb lattice, and the state with Abelian chiral spin liquid topological order on the triangular lattice.
Despite extensive investigations, a topological state that hosts Majorana edge modes in the magnetic field-induced quantum disordered state of the Kitaev candidate material $α$-RuCl$_3$ has been hotly debated. To gain more insight into this issue, we measured the thermal Hall conductivity $κ_{xy}$ of various samples grown by the Bridgman method. The results show that the half-integer quantum thermal Hall effect is intimately related to the magnitude of longitudinal thermal conductivity and the Néel temperature at zero field, both of which are sample dependent. Samples exhibiting the half-integ…
Motivated by experimental observations, Samajdar et al. [Nature Physics 15, 1290 (2019)] have proposed that the insulating Neel state in the parent compounds of the cuprates is proximate to a quantum phase transition to a state in which Neel order coexists with semion topological order. We study the manner in which proximity to this transition can make the phonons chiral, by inducing a significant phonon Hall viscosity. We describe the spinon-phonon coupling in a lattice spinon model coupled to a strain field, and also using a general continuum theory constrained only by symmetry. We find a no…
To probe the peculiar excitations spinons and magnetic monopoles in the quantum spin ice candidate Pr2Zr2O7, we studied the low-temperature thermal Hall conductivity (\k{appa}xy) and thermal conductivity (\k{appa}xx) of Pr2Zr2O7 single crystal with magnetic fields applied along the [111] axis. The magnetic field dependencies of \k{appa}xx suggest the roles of magnetic excitations in thermal conductivity, that is, the emergent magnetic monopoles can transport heat at T > 1.4 K and spinons mainly scatter phonons at lower temperatures. The finite \k{appa}xy was observed at low fields of several T…
Topological semimetals are a new class of metallic materials, which exist at band fillings that ordinarily correspond to insulators or compensated accidental semimetals with zero Luttinger volume. Their metallicity is a result of nontrivial topology in momentum space and crystal symmetry, wherein topological charges may be assigned to point band-touching nodes, preventing gap opening, unless protecting crystal symmetries are violated. These topological charges, however, are defined from noninteracting band eigenstates, which raises the possibility that the physics of topological semimetals may…
A recent experiment has reported oscillations of the thermal conductivity of $α$-RuCl$_3$ driven by an in-plane magnetic field that are reminiscent of the quantum oscillations in metals. At first glance, these observations are consistent with the presence of the long-sought-after spinon Fermi surface state. Strikingly, however, the experiment also reported vanishing thermal Hall conductivity coexisting with the oscillations of the longitudinal one. Such absence of the thermal Hall effect must originate from crystalline symmetries of $α$-RuCl$_3$. But if the system was a traditional spinon ferm…
Separation of spin and charge in paired spin-singlet quantum Hall states
我们提出了一系列成对的自旋单态量子霍尔态，它表现出自旋和电荷自由度的分离。这些态的基本激发态是自旋子（自旋为-1/2且电荷为零）或分数荷子（电荷为+/-1/2m +1且自旋为零），它们的填充分数ν=2/（2 m +1），其中m为奇数。这些激发的辫子统计是非阿贝尔的。在这些状态中自旋和电荷分离的机制是拓扑的：自旋和电荷激发通过与p波配对凝聚体中的涡旋结合而被释放。我们简要地讨论相关的，阿贝尔自旋单态和可能的过渡。
Fractional Quantum Geometry in Topological Mott Regime
International Center for Quantum Materials, School of Physics, Peking University（北京大学物理学院量子材料国际中心）；Beijing Key Laboratory of Quantum Devices（北京量子器件重点实验室）；Collaborative Innovation Center of Quantum Matter（量子物质协同创新中心）
Thermodynamic and dynamical properties of a model of Dirac fermions with a deconfined quantum critical point (DQCP) separating an interaction-generated quantum spin-Hall insulator from an s-wave superconductor [Nature Comm.~{\bf 10}, 2658 (2019)] are studied by quantum Monte Carlo simulations. Inside the deconfined quantum critical region bound by the single-particle gap, spinons and spinless charge-2e skyrmions emerge. Since the model conserves total spin and charge, and has a single length scale, these excitations lead to a characteristic linear temperature dependence of the uniform spin and…
Fractionalization from Kinetic Frustration in Doped Two-Dimensional SU(4) Quantum Magnets
Technical University of Munich（慕尼黑工业大学）；Munich Center for Quantum Science and Technology (MCQST)（慕尼黑量子科学与技术中心）；Institute for Theoretical Physics, ETH Zurich（苏黎世联邦理工学院理论物理研究所）
Hall-Lorenz ratio of YBa2Cu3O7 using Ionization energy based Fermi-Dirac statistics and charge-spin separation
在考虑了电离能的Fermi-Dirac统计和Fermi和电荷自旋分离液体共存的情况下，数值求解了热容、热导率和Hall-Lorenz比随温度的变化特性.热磁电子性质完全是自旋和电荷载流子的性质，因此声子的贡献被忽略了。对于过掺杂的YBaPDMATHABMN Cu $_3$ O $_{7-δ}$，如果满足$E_I$ $<$ $T_c$与电阻率的关系和没有自旋对（$T^*$ = 0），也得到了Hall-Lorenz比与温度（$T$）的线性关系.在$T_c$以上的$ab$ -平面中，基于纯的和电子污染的电荷自旋分离液体的热导率被发现随着$T$的减小而增加，作为与$T$成反比的结果。热容量的$T$依赖性也被突出，这定性地符合实验结果。
Observation of extended scattering continua characteristic of spin fractionalization in the 2D frustrated quantum magnet Cs2CuCl4 by neutron scattering
Realistic model Hamiltonians for quantum spin liquids frequently exhibit a large separation of energy scales between their elementary excitations. At intermediate, experimentally relevant temperatures, some excitations are sparse and hop coherently, whereas others are thermally incoherent and dense. Here we study the interplay of two such species of quasiparticle, dubbed spinons and visons, which are subject to nontrivial mutual statistics -- one of the hallmarks of quantum spin liquid behaviour. Our results for $\mathbb{Z}_2$ quantum spin liquids show an intriguing feedback mechanism, akin to…
Recently Chern insulators with Chern number $C=1$ and $C=2$ in zero (or very small) magnetic field have been observed in two moire graphene systems: twisted bilayer graphene and ABC trilayer graphene, both aligned with a hexagonal Boron-Nitride (h-BN) substrate. These Chern insulator states arise due to many body effects in the Chern bands of these systems when they are partially filled to a total integer filling $ν_T = 1,3$ (including spin and valley degrees of freedom). A simple possible explanation is from Hartree-Fock mean field theory which predicts valley and spin polarization in the zer…
Emergent Gauge Flux and Spin Ordering in Magnetized Triangular Spin Liquids: Applications to Hofstadter-Hubbard Model
International Center for Quantum Materials, School of Physics, Peking University（北京大学物理学院量子材料中心）；Beijing Key Laboratory of Quantum Devices, Peking University（北京大学北京量子器件重点实验室）；Collaborative Innovation Center of Quantum Matter（量子物质协同创新中心）
Spin-orbit coupling in the metallic and spin-liquid phases of Na4Ir3O8
最近有人提出，Na 4 Ir 3 O 8在环境压力下是弱莫特绝缘体，支持具有自旋费米表面的三维自旋液相。这一提议与最近的实验结果一致，即材料在增加压力或掺杂时变成金属。在这项工作中，我们调查的自旋轨道耦合所产生的5d Ir时刻在金属和自旋液相的Na 4 Ir 3 O 8的效果。导出了赝自旋j=1/2 Ir态的有效哈伯德模型，并研究了它对金属相和自旋液相的影响。特别是，该模型导致增强威尔逊比和强的温度依赖性的霍尔系数。
Emergent Symmetry-Protected Topological Phases via Polyakov Confinement in Quantum Spin Systems
National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University（南京大学固体微结构物理实验室和物理系）；Collaborative Innovation Center of Advanced Microstructures, Nanjing University（南京大学先进微结构协同创新中心）；Jiangsu Key Laboratory of Quantum Information Science and Technology, Nanjing University（南京大学江苏省量子信息科学与技术重点实验室）
We report a study on the specific heat and heat transport of Tb$_2$Ti$_{2-x}$Zr$_x$O$_7$ ($x =$ 0, 0.02, 0.1, 0.2, and 0.4) single crystals at low temperatures and in high magnetic fields. The magnetic specific heat can be described by the Schottky contribution from the crystal-electric-field (CEF) levels of Tb$^{3+}$, with introducing Gaussian distributions of the energy split of the ground-state doublet and the gap between the ground state and first excited level. These crystals has an extremely low phonon thermal conductivity in a broad temperature range that can be attributed to the scatte…
In strongly correlated materials, quasiparticle excitations can carry fractional quantum numbers. An intriguing possibility is the formation of fractionalized, charge-neutral fermions, e.g., spinons and fermionic excitons, that result in neutral Fermi surfaces and Landau quantization in an insulator. While previous experiments in quantum spin liquids, topological Kondo insulators, and quantum Hall systems have hinted at charge-neutral Fermi surfaces, evidence for their existence remains far from conclusive. Here we report experimental observation of Landau quantization in a two dimensional (2D…
