Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session E37: Kagome LatticesFocus
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Sponsoring Units: GMAG DCMP DMP Chair: Jeffrey Quilliam, Universite de Sherbrooke Room: BCEC 206A |
Tuesday, March 5, 2019 8:00AM - 8:12AM |
E37.00001: NMR Investigation of the Breathing Kagome Lattice in Li2In1-xScxMo3O8 Aimé Verrier, Mariam El-Amine, Xavier Bazier-Matte, Haidong Zhou, Ryan P Sinclair, Jeffrey Quilliam We report 7Li NMR measurements on Li2In1-xScxMo3O8 at concentrations x=0, 0.6 and 1. The results are compared with those of other groups on the end members of the series [1] and with previous work using muon spin rotation (µSR) [2]. The sample dependence and the effects of pressure on the NMR spectra and on the temperature dependence of the spin-lattice relaxation will be discussed, as well as their implications for possible spinon excitations in the spin liquid regime at intermediate Sc concentration. |
Tuesday, March 5, 2019 8:12AM - 8:24AM |
E37.00002: Thermal transport properties of S = 1/2 Cd-kapellasite Masatoshi Akazawa, Hayato Doki, Kaori Sugii, Masaaki Shimozawa, Minoru Yamashita, Hyun-Yong Lee, Naoki Kawashima, Ryutaro Okuma, Zenji Hiroi, Jung Hoon Han In recent years the thermal Hall effect has gained a great interest as an important signature of the topology. This effect has been observed in paramagnetic phase of kagome antiferromagnets, volborthite and Ca-kapellasite [1]. These thermal Hall conductivities (κxy) are shown to be well reproduced by Schwinger-boson mean field theory by tuning the Dzyaloshinskii-Moriya interaction D and the exchange energy J as fitting parameters. In this talk, we report further evidence supporting the agreement between the experiment and theory from thermal Hall measurements in Cd-kapellasite CdCu3(OH)6(NO3)2 H2O which has a smaller J/kB ~ 45 K than that of Ca-kapellasite. We find not only that κxy of Cd-kapellasite is also well reproduced by the theory, but also that the peak temperature in κxy is shifted to a lower temperature with a larger value in κxy as expected by the theory. The good scaling of these kagome materials strongly indicates that a kagome antiferromagnet has a common thermal Hall effect of the kagome spins. [1]H. Doki, M. Akazawa, H. Y. Lee et al., Phys. Rev. Lett. 121, 097203 (2018). |
Tuesday, March 5, 2019 8:24AM - 8:36AM |
E37.00003: Structural Phase Transitions in the S=1/2 Kagome Antiferromagnets Barlowite and Claringbullite Alyssa Henderson, Lianyang Dong, Sananda Biswas, Hannah I Revell, Yan Xin, John Schlueter, Roser Valenti, Theo Siegrist Barlowite (Cu4(OH)6FBr) and claringbullite (Cu4(OH)6FCl) are atacamite minerals related to the quantum spin liquid (QSL) candidate herbertsmithite ZnCu3(OH)6Cl2, the popular S = ½ antiferromagnet with a geometrically perfect kagome lattice. The kagome lattices of claringbullite and barlowite are stacked perfectly on top of one another and show promise as QSL candidates. Experiments suggest that at room temperature both materials have a hexagonal crystal structure with P63/mmc symmetry and undergo temperature-dependent phase transitions. Ab-initio density functional theory calculations were performed to explain these structural phase transitions. The transitions are likely influenced by the presence of defects, so it is expected that the transition temperature varies from sample to sample and will be different for crystals grown by different methods. |
Tuesday, March 5, 2019 8:36AM - 9:12AM |
E37.00004: Interplay of charge and spin degrees of freedom in Mo3O13 cluster Mott insulators Invited Speaker: Arash Akbari-Sharbaf A promising approach to understanding the complexities of experimental quantum spin liquid candidates is to search for a way to tune the microscopic Hamiltonian and study changes in the resulting magnetic phases. In this talk I will present recent developments in a new class of highly tunable Mo3O13 cluster Mott insulators. This family of materials can be viewed as a breathing kagome lattice (BKL) of Mo ions, where the corner-sharing up and down triangles have two different sizes. In the compounds Li2In1-xScxMo3O8 the breathing parameter (λ) changes non-monotonically with Sc concentration (x), tuning the system from an antiferromagnetic Mott insulator for large λ, to a quantum spin liquid for small λ [1]. For large breathing parameter electrons become confined on the small triangles forming spin-1/2 Mo3 clusters on a triangular lattice with antiferromagnetic exchange coupling between them, leading to long range antiferromagnetic order. On the other hand, for small breathing parameter electrons are no longer confined to individual Mo3 clusters but can tunnel between adjacent clusters, leading to a novel long range plaquette charge order (PCO) [2]. Our thermodynamic and muon spin rotation (μSR) measurements, suggest that the PCO coincides with a high degree of spin frustration and leads to a quantum spin liquid ground state, with gapless spinon excitations. The tunability of these materials can be extended to lower and higher breathing parameter in several related Mo-oxide materials, revealing additional quantum spin liquids and even ferromagnetism. |
Tuesday, March 5, 2019 9:12AM - 9:24AM |
E37.00005: Pressure and doping effects on the low-field anomalous magnetism in kagome Co3Sn2S2 Hung-Cheng Wu, Po-Jung Sun, Dong-Jie Hsieh, D Chandrasekhar Kakarla, Ching-Wu Chu, Hung-Duen Yang Polycrystalline samples Co3Sn2S2+x (0 ≤ x ≤ 0.34) and (Co1-xMx)3Sn2S2.26 (M = Ni and Fe, 0 ≤ x ≤ 0.05) have been synthesized using solid-state-reaction and characterized by X-ray diffraction (XRD) and electron probe microanalyzer (EPMA). Basically, we are able to reproduce the phase diagram (so-called A phase) as previously reported with negligible sample dependent effect. Furthermore, following the similar procedure and analysis, a so-called A' phase within phase can be sketched in H-T phase diagram of Co3Sn2S2. Under the effects of external high-pressure and chemical substitutions, the anomalous magnetisms (A and A' ) in low magnetic field show a significant change. The possible origin of the field-induced A' phase could be ascribed to the non-collinear skyrmion-like phenomena. These striking findings provide a new candidate in spin-frustrated systems to explore the complexity of magnetic-field-induced magnetism. |
Tuesday, March 5, 2019 9:24AM - 9:36AM |
E37.00006: Spin dynamics in the antiferromagnetic Heisenberg model on a pyrochlore slab Preetha Saha, Depei Zhang, Gia-Wei Chern Unconventional magnetic states such as spin liquids and spin glasses continue to attract the interest of researchers in magnetism. Recently, considerable effort has been focused on understanding their dynamical signatures [1-2]. We present our study on deterministic spin precession dynamics using energy conserving Landau-Lifshitz equation on a geometrically frustrated magnet. The lattice constitutes of a triangular arrangement of bipyramids with classical antiferromagnetic Heisenberg interaction. Such a lattice structure is realized in frustrated SrCr9Ga12-9pO19 [SCGO(p)] compounds [3]. Monte Carlo simulations are used to thermalize the system, which is then used as the initial state for the dynamical studies. We explore the temperature, wave vector and frequency dependence in the dynamical structure factor and the corresponding time dependent correlation functions of the model. Dynamics simulations is further used to estimate the extent to which transport of spin excitations in the lattice conform with phenomenological concept of spin diffusion. |
Tuesday, March 5, 2019 9:36AM - 9:48AM |
E37.00007: Chiral superconductivity with full Bogoliubov Fermi surface in a doped Kagome spin-liquid state. Fan Yang, Yifan Jiang, Hong Yao We employ a large-scale variational Monte-Carlo simulation to investigate the lightly doped t-J model on the Kagome lattice. We propose several new variational states which smoothly connect to the previously studied uniform 0-flux or U(1) $\pi$-flux states. By comparing the energies of a variety of trail-states at several system-sizes, we find that the state with lowest energy is a chiral superconducting state with full Bogoliubov Fermi surface, which can be analogous to the Fulde-Ferrell-Larkin-Ovchinnikov state. The physical properties of this new state and the experimental consequences of the existence of Bogoliubov Fermi surface in this superconducting state are discussed. |
Tuesday, March 5, 2019 9:48AM - 10:00AM |
E37.00008: A single-layer infinite projected entangled-pair state study of the chiral antiferromagnetic Heisenberg model on Kagome lattice Reza Haghshenas, Donna Sheng, Shoushu Gong In this talk, we present the study of the chiral antiferromagnetic Heisenberg model on Kagome lattice by using the infinite projected entangled-pair state ansatz. We discuss how to develop an efficient optimization algorithm in the framework of the single-layer tensor network with reduced computation cost O(D^9), where D is the so-called bond dimension of local tensors. We show that the algorithm is stable, providing accurate results similar to previous double-layer tensor network ansatz. We compare the extracted phase diagram with previous DMRG study and additionally show that only for strong chrial couplings the correlation length, extracted from the transfer matrix, reaches a fixed value for the largest bond dimensions, representing a gaped chiral state. |
Tuesday, March 5, 2019 10:00AM - 10:12AM |
E37.00009: Magnetic clustering in frustrated Heisenberg magnets Tomonari Mizoguchi, Ludovic Jaubert, Roderich Moessner, Masafumi Udagawa Fractionalization is one of the fundamental properties of magnets with nontrivial topological character. For example in spin ice, fractionalized degrees of freedom take the form of magnetic monopoles which serve as elementary excitations with a conserved quantum number, their magnetic charge. Recently, it has been pointed out that the clustering of such topological charges leads to characteristic patterns in static structure factors, which we named half moons, distinct form the pinch points that serve as indicators of a Coulomb phase. |
Tuesday, March 5, 2019 10:12AM - 10:24AM |
E37.00010: Phases of the Chiral-Heisenberg Kagome Antiferromagnet Jackson Pitts, Finn Buessen, Roderich Moessner, Simon Trebst, Kirill Shtengel The ground state degeneracy of the classical kagome Heisenberg antiferromagnet (KHAFM) is remarkably similar to that of the kagome chiral model (KCM) whose Hamiltonian consists of the scalar spin chiralities on the triangles of the lattice. However, models containing both types of interactions have reduced degeneracies. If chiral terms are introduced uniformly, the √3×√3 state lifts from the ground state manifold, but if they are introduced with staggered sign, the q=0 state is excluded instead. Only once the Heisenberg terms are entirely eliminated are states of both types again ground states. This has drastic effects on the order-by-disorder mechanism that drives coplanar ordering in the KHAFM. Our Monte Carlo simulations demonstrate a more discriminating selection effect in the intermediate models. Furthermore, even in the case of the pure KCM, only the √3×√3 structure is observed. We explain this by counting the soft modes of the KCM’s ground states. Only states of √3×√3 structure have sufficient populations of soft modes to drive the system to order. Due to an extra degeneracy of the KCM this structure exists on a large set of states forming a classical spin liquid. |
Tuesday, March 5, 2019 10:24AM - 10:36AM |
E37.00011: ABSTRACT WITHDRAWN
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Tuesday, March 5, 2019 10:36AM - 10:48AM |
E37.00012: Temperature dependence of butterfly effect in a classical many-body system Thomas Bilitewski, Subhro Bhattacharjee, Roderich Moessner We study the chaotic dynamics in a classical many-body system of interacting spins on the kagome lattice. We characterise many-body chaos via the butterfly effect as captured by an appropriate out-of-time-ordered commutator. Due to the emergence of a spin liquid phase, the chaotic dynamics extends all the way to zero temperature. We thus determine the full temperature dependence of two complementary aspects of the butterfly effect: the Lyapunov exponent, μ, and the butterfly speed, vb, and study their interrelations with usual measures of spin dynamics such as the spin-diffusion constant, D and spin-autocorrelation time, τ. We find that they all exhibit power law behaviour at low temperature, consistent with scaling of the form D∼vb2/μ and τ-1−T. The vanishing of μ∼T0.48 is parametrically slower than that of the corresponding quantum bound, μ∼T, raising interesting questions regarding the semi-classical limit of such spin systems. |
Tuesday, March 5, 2019 10:48AM - 11:00AM |
E37.00013: A mechanism for thermal Hall effect in Mott insulating spin liquid Yonghao Gao, Gang Chen We study the origin of thermal Hall effect from the spinon transport in a U(1) spinon metal. The external magnetic field, that polarizes the spins, effectively generates an internal U(1) gauge flux for the spinons and twists the spinon motion through the antisymmetric interaction. Such a mechanism for Lorentz force generation differs fundamentally from the induction of the internal U(1) gauge flux in the weak Mott insulating regime from the charge fluctuations. We apply this understanding to the specific cases of spinon metals in Kagome lattice and hyperkagome lattice. We carry out a numerical calculation of the thermal Hall conductivity within the linear response theory and discuss the relevance with the thermal transport measurement in Kagome materials volborthite and kapellasite. |
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