Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session X5: Frustrated Magnetism: Kagome LatticeFocus
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Sponsoring Units: GMAG DMP Chair: Oleg Tchernyshyov, Johns Hopkins University Room: 301 |
Friday, March 18, 2016 8:00AM - 8:36AM |
X5.00001: A Dichotomy of the Spin Liquid and the Correlated Impurities in Herbertsmithite Invited Speaker: Tianheng Han It is debatable whether RVB spin liquids exist in kagome systems.~ Enthusiasm in spin-1/2 kagome antiferromagnets gained extra momentum from the observation of a spinon continuum in ZnCu3(OD)6Cl2 (herbertsmithite).~ In low-energy limit, where insightful many-body theories exist, impurities complicate experimental interpretations. ~Two important progresses were made in the past year.~ Single-crystalline 17O NMR experiment provided evidence for pristine kagome layers and a spin gap. ~Below the spinon continuum's energies, neutron scattering measurements revealed 3 dimensional spin correlations, which likely originate from the impurities.~ I will present the intrinsic-extrinsic dichotomy in ZnCu3(OD)6Cl2 as well as my thoughts on future directions. [Preview Abstract] |
Friday, March 18, 2016 8:36AM - 8:48AM |
X5.00002: Fractionalized spin-wave continuum in kagome spin liquids Jia-Wei Mei, Xiao-Gang Wen Motivated by spin-wave continuum (SWC) observed in recent neutron scattering experiments in Herbertsmithite, we use Gutzwiller-projected wave functions to study dynamic spin structure factor $S(\mathbf{q},\omega)$ of spin liquid states on the kagome lattice. Spin-1 excited states in spin liquids are represented by Gutzwiller-projected two-spinon excited wave functions. We investigate three different spin liquid candidates, spinon Fermi-surface spin liquid (FSL), Dirac spin liquid (DSL) and random-flux spin liquid (RSL). FSL and RSL have low energy peaks in $S(\mathbf{q},\omega)$ at $K$ points in the extended magnetic Brillouin zone, in contrast to experiments where low energy peaks are found at $M$ points. There is no obviuos contradiction between DSL and neutron scattering measurements. Besides a fractionalized spin ({\it i.e.} spin-1/2), spinons in DSL carry a fractionalized crystal momentum which is potentially detectable in SWC in the neutron scattering measurements. [Preview Abstract] |
Friday, March 18, 2016 8:48AM - 9:00AM |
X5.00003: A mean-field study of the Hubbard model on the kagome lattice Matthew Enjalran The experimental work on the herbertsmithite compound, ZnCu$_3$(OH)$_6$Cl$_2$, almost a decade ago ignited intense interest in the field of frustrated magnetism because it represented the best material realization of a spin-$1/2$ Heisenberg antiferromagnet (AFM) on the kagome lattice and its ground state was a gapless spin liquid. Many theoretical and numerical studies of the quantum Heisenberg AFM on the kagome lattice have been performed since and have coalesced around the general consensus of a small gapped spin liquid ground state for the model. Although there is not currently a metallic kagome material system, the work on ZnCu$_3$(OH)$_6$Cl$_2$ has motivated theoretical and numerical investigations of itinerant electrons on the kagome lattice. We contribute to this pursuit by studying the single band Hubbard model on the kagome lattice, where the frustration can be tuned by adjusting the hopping along different bonds, $t_1$ and $t_2$; however, we are mainly interested in the isotropic limit, $t_1 = t_2 = t$. We report preliminary results on the low temperature correlations in the half filled model as a function of frustration and interaction strength in the mean-field, Hartree-Fock, limit. [Preview Abstract] |
Friday, March 18, 2016 9:00AM - 9:12AM |
X5.00004: Structure and Physical Properties of SrNiRu$_{\mathrm{5}}$O$_{\mathrm{11}}$ Single Crystals: A New Frustrated R-type Ferrite Based on Ordered Kagome Nets Lance De Long, Larysa Shlyk, Rainer Niewa Single crystals of the $R$-type ferrite SrNiRu$_{\mathrm{5}}$O$_{\mathrm{11}}$ were grown from a chloride flux. The hexagonal crystal structure contains ruthenium located on Kagome nets, distorted due to formation of Ru--Ru dumbbells via metal-metal bonding. SrNiRu$_{\mathrm{5}}$O$_{\mathrm{11}}$ does not show long-range magnetic order down to 4.5 K. The low-temperature magnetic susceptibilities, $\chi_{\mathrm{\mathbf{\bot }}}$ and $\chi _{\mathrm{\mathbf{//}}}$ \textbf{\textit{c}}\textbf{-}axis, diverge as $T^{\mathrm{\thinspace -0.3}}$, and the electric resistivity varies as $T^{\mathrm{1.6}}$ below 40 K, which is typical of non-Fermi liquid materials. This anomalous behavior might originate from the competition between residual magnetic interactions among Ni$^{\mathrm{2+}}$ ($S \quad =$ 1) spins and geometrical frustration on the two-dimensional Kagome lattice of Ru$^{\mathrm{3+}}$ ($S \quad =$ 1/2) spins. The transverse magnetoresistivity $\rho_{xy}$, of a SrNiRu$_{\mathrm{5}}$O$_{\mathrm{11}}$ single crystal at constant temperature $T \quad =$ 5 K for current-magnetic-field configurations, \textbf{\textit{J }} $\bot $ \textbf{\textit{H \textbar \textbar c}}-axis and \textbf{\textit{J \textbar \textbar H }} $\bot $ \textbf{\textit{c}}\textbf{-}axis, reveals no anomalous contribution, which is typical for non-magnetic materials. Fits of the heat capacity data below 10 K require a dominant, but unusual electronic term of the form $C_{el} \quad = \quad \gamma T^{\mathrm{1.2}}$, which is expected for massless Dirac fermion states in topological insulators or spin liquid phases. [Preview Abstract] |
Friday, March 18, 2016 9:12AM - 9:24AM |
X5.00005: Local probe study of Sr-Vesignieite Aimé Verrier, Jeffrey Quilliam, Fabrice Bert, Philippe Mendels, David Boldrin, Andrew Wills We discuss the results of local probe measurements (NMR and $\mu$SR) on a powder sample of $\mathrm{SrCu_3V_2O_8(OH)_2}$ (Sr-Vesignieite)[D. Boldrin and A. S. Wills, J. Mat. Chem. C 3, 4308(2015)], a spin-1/2 kagome lattice with antiferromagnetic interactions.$^{63,65}$Cu zero-field NMR and $^{51}$V NMR (in-field) reveal static magnetism at low temperatures and allow us to measure the intrinsic local susceptibility of the kagome lattice. Muon spin rotation ($\mu$SR) experiments also demonstrate static magnetism at low $T$. We discuss the possible role of the Dzyaloshinsky-Moriya interaction and the proximity of this material to a quantum critical point between ordered and quantum spin liquid phases. [Preview Abstract] |
Friday, March 18, 2016 9:24AM - 9:36AM |
X5.00006: Hidden Order in Spin-Liquid Gd$_3$Ga$_5$O$_{12}$ Joseph Paddison, Henrik Jacobsen, Oleg Petrenko, Maria Teresa Fern\'{a}ndez-D\'{i}az, Pascale Deen, Andrew Goodwin Frustrated magnetic materials are promising candidates for new states of matter because lattice geometry suppresses conventional magnetic dipole order, potentially allowing non-dipole (``hidden") order to emerge in its place. However, an atomic-scale model of a hidden-order state has been difficult to obtain because microscopic probes are not directly sensitive to hidden order. We use a combination of neutron-scattering experiments and reverse Monte Carlo refinements to develop a model of the spin-liquid state in the canonical frustrated magnet Gd$_3$Ga$_5$O$_{12}$. We show that this state exhibits a hidden order which has three unusual properties. First, it is a collective phenomenon, in which multipoles are formed from ten-spin loops. Second, it is long-range, with a diverging correlation length. Third, it is a consequence of the interplay between antiferromagnetic spin correlations and local planar magnetic anisotropy, which allows it to be indirectly observed in our neutron-scattering experiments. [Preview Abstract] |
Friday, March 18, 2016 9:36AM - 9:48AM |
X5.00007: Topologically non-trivial electronic and magnetic states in doped copper Kagome lattices Daniel Guterding, Harald O. Jeschke, Roser Valenti We present a theoretical investigation of doped copper kagome materials based on natural minerals Herbertsmithite [ZnCu$_3$(OH)$_6$Cl$_2$] and Barlowite [Cu$_4$(OH)$_6$FBr]. Using ab-initio density functional theory calculations we estimate the stability of the hypothetical compounds against structural distortions and analyze their electronic and magnetic properties. We find that materials based on Herbertsmithite present an ideal playground for investigating the interplay of non-trivial band-topology and strong electronic correlation effects. In particular, we propose candidates for the Quantum Spin Hall effect at filling 4/3 and the Quantum Anomalous Hall effect at filling 2/3. For the Barlowite system we point out a route to realize a Quantum Spin Liquid. [Preview Abstract] |
Friday, March 18, 2016 9:48AM - 10:00AM |
X5.00008: DMRG studies of the frustrated kagome antiferromagnets and the application to volborthite Shou-shu Gong, D. N. Sheng, Kun Yang Motivated by the recent magnetization measurements on the high-quality single crystals of the kagome antiferromagnet volborthite, we study the ground state and magnetization properties of two kagome models proposed from the electronic structure simulations, which treat the volborthite as either the coupled trimers or the coupled frustrated chains on the kagome lattice. We study the models using density-matrix renormalization group on the cylinder geometry with the system width up to 4 legs. We find a quantum phase diagram of the models with changing couplings, and identify the magnetic properties of each phase. In the antiferromagnetic phases, we also study the magnetization curve and the different phases in the magnetic field. Finally, we compare the magetization properties of the models with the experimental observations of volborthite. [Preview Abstract] |
Friday, March 18, 2016 10:00AM - 10:12AM |
X5.00009: Spin-wave analysis of a broad magnetization plateau in volborthite Edward Parker, Leon Balents Volborthite ($\mathrm{Cu_3 V_2 O_7 (OH)_2 \cdot 2H_2O}$) is a system comprised of spin-$1/2$ ions forming quasi-2D layers of Kagom\'{e} lattices. It displays two striking experimental features: strong geometric frustration (with a magnetic ordering temperature more than two orders of magnitude below its Curie temperature), and an extremely broad $m = \frac{1}{3} m_\text{sat}$ magnetization plateau extending over a range of more than 100 T. Density functional theory calculations suggest that it has a complicated anisotropic spin coupling structure with both ferromagnetic and antiferromagnetic first- and second-nearest-neighbor bonds. We present results for the classical phase diagram for this system, focusing on how the upper and lower critical fields of the magnetization plateau depend on the exchange couplings. We also present a semiclassical large-$S$ expansion, and show how including the leading quantum corrections in $1/S$ gives a magnon self-energy that shifts the classical values for the plateau's critical fields. [Preview Abstract] |
Friday, March 18, 2016 10:12AM - 10:24AM |
X5.00010: Changing the Electron Count in Spin Liquids Zachary Kelly, Tyrel McQueen Materials which possess the resonating valence bond (RVB) ``spin-liquid'' state have been long sought after by scientists due to their predicted exotic properties. Several materials have been identified as potential spin liquid candidates and laboratory studies have only just begun to provide insight into the properties of these materials and their theoretical description. Recently theoretical calculations predict doping of a spin liquid could lead to a rich and unique phase diagram including complex magnetic states, Dirac metal behavior, and superconductivity. We report the results of structural and physical property characterizations of newly synthesized doped candidate spin liquids. [Preview Abstract] |
Friday, March 18, 2016 10:24AM - 10:36AM |
X5.00011: A Kagome Map of Spin Liquidsx Karim Essafi, Owen Benton, Ludovic D. C. Jaubert Competing interactions in frustrated magnets prevent ordering down to very low temperatures and stabilize exotic highly degenerate phases where strong correlations coexist with fluctuations. We study a very general nearest-neighbour Heisenberg spin model Hamiltonian on the kagome lattice which consist of Dzyaloshinskii-Moriya, ferro- and antiferromagnetic interactions. We present a three-fold mapping which transforms the well-known Heisenberg antiferromagnet (HAF) and XXZ model onto two lines of time-reversal Hamiltonians. The mapping is exact for both classical and quantum spins, {\it i.e.} preserves the energy spectrums of the HAF and XXZ model. As a consequence, our three-fold mapping gives rise to a connected network of quantum spin liquids centered around the Ising antiferromagnet. We show that this quantum disorder spreads over an extended region of the phase diagram at linear order in spin wave theory, which overlaps with the parameter region of Herbertsmithite ZnCu$_3$(OH)$_6$Cl$_2$. At the classical level, all the phases have an extensively degenerate ground-state which present a variety of properties such as ferromagnetically induced pinch points in the structure factor and spontaneous scalar chirality which was absent in the original HAF and XXZ models. [Preview Abstract] |
Friday, March 18, 2016 10:36AM - 10:48AM |
X5.00012: Nature of Possible Z$_6$ symmetry breaking magnetic phases in frustrated hyperkagome iridate Ryuichi Shindou To obtain a comprehensive understanding of classical magnetism possible in frustrated hyperkagome iridate Na$_4$Ir$_3$O$_8$ (Na-438), we postulated additional lattice symmetries other than an exact crystal symmetry, and introduced a relatively simpler effective spin model for Na-438. Using Monte Carlo simulation and Luttinger-Tisza analysis, we derived a classical magnetic phase diagram for Na-438. We show that a Z$_6$ symmetry breaking magnetic phase is stabilized by the thermal order by disorder. Our finite-size scaling analysis reveals that the criticality of the ordering temperature of the Z$_6$ phase is characterized by the 3D XY universality class, where the system acquires effectively a higher symmetry than high-$T$ disorder phase (dubbed as “emergent U(1) symmetry”). For a finite size system, an intermediate temperature regime appears below the ordering temperature, where the spin anisotropy term becomes effectively irrelevant and spin ordering develops in the U(1) symmetric way. We showed that this crossover phenomena can be well accounted for in terms of the 3-d ferromagnetic Z$_6$ Potts model. Based on this crossover behavior, we introduced a possible phenomenology of low-temperature magnetic behaviors of polycrystalline Na-438. Reference: arXiv.1509.01002 [Preview Abstract] |
Friday, March 18, 2016 10:48AM - 11:00AM |
X5.00013: Competing phases of S=1 XXZ model on Kagome lattice zhenyue zhu, Steven White We numerically study the S=1 XXZ model on the kagome lattice with the Density matrix renormalization group. We focus on the two types of expected magnetic order, $Q=0$ and $\sqrt{3}\times \sqrt{3}$. As a function of the coupling $\Delta$ for the $S_zS_z$ terms, we find two possible phase transitions. For $\Delta < \Delta_1$, we find that the $Q=0$ state has lower energy, but the difference between these two magnetic ordered phase is very small. For $\Delta_1< \Delta < \Delta_2$, $\sqrt{3}\times \sqrt{3}$ magnetic ordered state is the ground state. For $\Delta > \Delta_2$, we find that the magnetic ordered phases disappears, entering a magnetic disordered phase. We find a close competition between a trimerized phase and a hexagon singlet phase, which is consistent with recent numerical studies of S=1 Heisenberg model on the Kagome lattice. [Preview Abstract] |
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