Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session S46: Kagome LatticeFocus
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Sponsoring Units: GMAG DMP Chair: Turan Birol, University of Minnesota Room: 708 |
Thursday, March 5, 2020 11:15AM - 11:51AM |
S46.00001: Kondo effect in a spinon metal Invited Speaker: Andrej Zorko The Kondo screening of localized impurities possessing magnetic moments is traditionally associated with exchange scattering of conduction electrons. This nontrivial display of many-body physics is common to ordinary metals and was recently found also in various more complex conducting systems, such as quantum dots, graphene, and topological insulators. Moreover, the Kondo effect was theoretically predicted for certain electric insulators in which emergent fractional magnetic excitations can effectively take over the role of itinerant electrons in screening the impurities’ magnetic moments [1-4]. |
Thursday, March 5, 2020 11:51AM - 12:03PM |
S46.00002: Dynamics of jammed spin liquid on the kagome bilayer Sheng Zhang, Preetha Saha, Depei Zhang, Seunghun Lee, Gia-Wei Chern The Heisenberg antiferromagnet on the kagome bilayer is one of the canonical frustrated spin systems. It also provides a basic model for the compound SCGO that triggered the interest in highly frustrated magnets. The source of the seemingly glassy behavior observed in SCGO at temperatures below $T_g \approx 3.5$ -- 7 K remains unclear even after decades of intensive study. In particular, previous works [1], including our own [2], seem to indicate that dilution alone does not engender a spin glass in its classical spin-liquid ground state. Instead, it is suggested that the glassy behavior likely originates from the interplay between disorder and the coplanarity tendency due to quantum fluctuations~[1,3]. In this work, we study the dynamical properties of an effective Hamiltonian that incorporates the collinear/coplanar tendency through a biquadratic spin interaction. We report unusual relaxation dynamics and the dynamical structure factor of the effective model and discuss their experimental implications. |
Thursday, March 5, 2020 12:03PM - 12:15PM |
S46.00003: Electron-nuclear hyperfine coupling in quantum kagome antiferromagnets from first-principles calculation and a reflection of the defect effect Shunhong Zhang, Yi Zhou, Feng Liu, Zheng Liu The discovery of ideal spin-1/2 kagome antiferromagnets Herbertsmithite and Zn-doped Barlowite represents a breakthrough in the quest for quantum spin liquids (QSLs), and nuclear magnetic resonance (NMR) spectroscopy plays a prominent role in revealing the quantum paramagnetism in these compounds. However, interpretation of NMR data that is often masked by defects can be controversial. Here, we show that the most significant interaction strength for NMR, i.e. the hyperfine coupling (HFC) strength, can be reasonably reproduced by first-principles calculations for these proposed QSLs. Applying this method to a supercell containing Cu-Zn defects enables us to map out the variation and distribution of HFC at different nuclear sites. This predictive power is expected to bridge the missing link in the analysis of the low-temperature NMR data. |
Thursday, March 5, 2020 12:15PM - 12:27PM |
S46.00004: Thermal conductivity of the quantum spin liquid candidate herbertsmithite Patrick Bourgeois-Hope, Pierre Lefloïc, Nicolas Doiron-Leyraud, Louis Taillefer, Philippe Mendels, Matias Velazquez Hosting a S = 1/2 system on a kagome lattice, herbertsmithite (ZnCu3(OH)6Cl2) is a leading candidate in the search for quantum spin liquids. Despite the absence of magnetic ordering down to very low temperature and several probes detecting a significant density of low-energy states, a debate persists on whether this material has gapless spinon excitations. Our thermal conductivity measurements down to 60 mK show no signs of the T-linear contribution to heat conduction that is expected from mobile spinons. Instead, our results suggest that the low-energy spin excitations in herbertsmithite are either localized or gapped. |
Thursday, March 5, 2020 12:27PM - 12:39PM |
S46.00005: Diverse S=1/2 distorted kagome Hamiltonians in titanium fluorides Harald Jeschke, Hiroki Nakano, Toru Sakai We determine the connection between highly frustrated kagome based Hamiltonians and a recently synthesized family of materials containing Ti3+ S = 1/2 ions [1]. With the help of a combination of all electron density functional theory and numerical diagonalization techniques, we establish the Heisenberg Hamiltonians for the distorted kagome antiferromagnets Rb2NaTi3F12, Cs2NaTi3F12, and Cs2KTi3F12. We determine magnetization curves in excellent agreement with experimental observations. Our calculations successfully clarify the relationship between the experimental observations and the magnetization-plateau behavior at 1/3 height of the saturation and predict characteristic behaviors under fields that are higher than the experimentally measured region. We demonstrate that the studied Ti(III) family of materials interpolates between the kagome strip and kagome lattice. Further members of this family of materials are also considered. |
Thursday, March 5, 2020 12:39PM - 12:51PM |
S46.00006: The origin of trimerized phase in S=1 kagome magnet Na2Ti3Cl8 Arpita Paul, Chia-Min Chung, Hitesh Changlani, Turan Birol The kagome magnet Na2Ti3Cl8 with S=1 spins undergoes a structural transition involving trimerization or breathing distortion of the underlying kagome lattice as the temperature lowers. We investigate the magnetic ground state of this compound by constructing a model spin Hamiltonian based on first-principles density functional theory and analyzing it using exact diagonalization and density matrix renormalization group methods. Along with the nearest neighbor Heisenberg and biquadratic exchanges, we propose a new exchange term fourth order in spins - ring exchange that does not originate from spin-orbit coupling and involves simultaneous hopping of electrons from one site to its two neighboring sites. The parameters that our first principles calculations give for the high temperature crystal structure place this compound to the ferroquadrapolar region of the phase diagram predicted by exact diagonalization and density matrix renormalization group calculations. We thus suggest that a spin - lattice coupling favors the trimerized phase over the quadrapolar phase, even though density functional theory alone does not predict a lattice instability. |
Thursday, March 5, 2020 12:51PM - 1:03PM |
S46.00007: Dynamical properties of site-diluted Heisenberg antiferromagnetic on the kagome bilayer Preetha Saha, Depei Zhang, Seung-Hun Lee, Gia-Wei Chern We present spin dynamical simulations of the site-diluted Heisenberg antiferromagnet with nearest neighbor interactions on a quasi-2D kagome bilayer. This geometrically frustrated lattice consists of two kagome layers connected by a triangular-lattice layer. We combine Monte Carlo method with precessional spin dynamics simulations to compute the dynamical structure factor of the classical spin liquid and study the thermal and dilution effects. The low frequency and long wavelength dynamics of the classical spin liquid in kagome bilayer is dominated by spin diffusion [1]. In the presence of spin vacancies, the dynamical properties of the diluted system can be understood within the two population picture [2,3]. The spin diffusion of the “correlated” spin clusters gives rise to an exponentially decaying autocorrelation function. On the other hand, the diffusive dynamics of the quasi-free “orphan” spins leads to a distinctive long time power-law tail in the autocorrelation function. We discuss the implications of our work for the glassy behaviors observed in the frustrated magnet SrCr9pGa12−9pO19(SCGO). |
Thursday, March 5, 2020 1:03PM - 1:39PM |
S46.00008: Search for simplex solid and spin liquid phases in highly frustrated S=1 antiferromagnets Invited Speaker: Hitesh Changlani Quantum spin liquids are enigmatic phases of matter characterized by the absence of symmetry breaking and conventional quasiparticles. The search for their realisation in actual magnetic materials has targeted, but is not limited to, materials involving the geometrically frustrated triangular, kagome and pyrochlore geometries with low spins. Indeed, while there have been significant efforts to synthesize quantum spin liquid materials in spin-1/2 systems in two dimensions, fewer efforts have been devoted to three dimensions and higher spins. In this talk, we show that both these criteria may be too restrictive. We thus expand our search to spin-1 frustrated antiferromagnets which are abundant in nature but where few theories or results exist to understand their general properties and behavior. Motivated by recent realizations of S=1 kagome and pyrochlore geometries, we address the question of their quantum many-body ground state. For kagome, a spin liquid state known as the Hexagonal Singlet State, motivated by the Affleck Kennedy Lieb Tasaki state in one dimension, is found to be competitive in energy. However, for the pure Heisenberg model it loses out to a symmetry broken trimerized (simplex solid) ground state, a conclusion we derive from density matrix renormalization group calculations. We show that this finding is relevant to the recently synthesized S=1 kagome material Na2Ti3Cl8 which shows a large trimerized distortion in its low temperature phase. For the S=1 pyrochlore case, our search bears fruit - we find a nearly idealized Heisenberg model in NaCaNi2F7. Our results show strong evidence for a quantum spin liquid phase based on both its static and dynamical properties. |
Thursday, March 5, 2020 1:39PM - 1:51PM |
S46.00009: Magnetoresistance Study of Kagome Artificial Spin Ice with Fibonacci Distortions Justin Woods, Barry W Farmer, Yong-Lei Wang, Wai-Kwong Kwok, Lance Eric De Long Nanofabrication techniques allow magnetic thin films to be lithographically patterned into arrays of interacting macro-spins designed to exhibit emergent physical properties. We study the effects of continuous symmetry breaking on the magnetoresistive behavior of frustrated Kagome (alt. honeycomb) ASI whose periodic lattice is aperiodically distorted by repeated application of a substitution algorithm: A Fibonacci sequence of binary digits is mapped into short (d1) and long (d2) primitive lattice translations, which alters the magnetic moments and angular coordination of the three-fold Kagome vertices. Kagome arrays with variable distortions are patterned in series to permit simultaneous longitudinal and transverse magnetoresistances measurements in external magnetic fields. The direction and magnitude of applied field was varied to produce distinct, interesting differences in the magnetoresistance response of the distorted Kagome arrays, compared to the undistorted arrays. |
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S46.00010: Tuning the Two-step Melting of Magnetic Order in Dipolar Kagome Ice by Quantum Fluctuations Yao Wang, Stephan Humeniuk, Yuan Wan Complex magnetic orders in frustrated magnets may exhibit rich melting processes when the magnet is heated toward the paramagnetic phase. In this talk, we show that one may tune such melting processes by quantum fluctuations. We consider a kagome lattice dipolar Ising model subject to transverse field and focus on the thermal transitions out of its magnetic ground state, which features a root 3 by root 3 magnetic unit cell. Our quantum Monte Carlo (QMC) simulation suggests that, at weak transverse field, the root 3 by root 3 order melts by way of an intermediate, magnetically charge ordered phase where the lattice translation symmetry is restored whilst the time reversal symmetry remains broken[1]. By contrast, at moderate transverse field, QMC simulation suggests the root 3 by root 3 order melts through a floating Kosterlitz-Thouless (KT) phase. The two distinct melting processes are likely separated by a multicritical point identified in Ref.[2]. |
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S46.00011: Non-coplanar magnetic order and topological magnons in tripod kagome antiferromagnet Yb3Mg2Sb3O14 Zhiling Dun, Owen Benton, Xiaojian Bai, Nicholas Butch, Haidong Zhou, Martin Mourigal Kagome antiferromagnet is one of the most studied models for geometrical frustration which is expected to be a topological magnon insulator in the presence of Dzyaloshinskii–Moriya interactions. The recent discovered tripod kagome materials provide us a platform to explore such ideas with strongly spin-orbit coupled rare earth ions. Using elastic neutron scattering measurements, we show that one of the tripod kagome compounds, Yb3Mg2Sb3O14, orders into a strongly non-coplanar magnetic ground state below 0.88 K which calls for large antisymmetric exchanges. Inelastic neutron scattering experiment on polycrystalline samples reveals both dispersive and flat magnon bands which can be fitted by an anisotropic exchange Hamiltonian derived from a symmetry analysis. Along with numerical calculations, our results unveil Yb3Mg2Sb3O14 as a candidate to host topological non-trivial magnon bands. |
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