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 manybody 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 [14]. 
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, GiaWei 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 spinliquid 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: Electronnuclear hyperfine coupling in quantum kagome antiferromagnets from firstprinciples calculation and a reflection of the defect effect Shunhong Zhang, Yi Zhou, Feng Liu, Zheng Liu The discovery of ideal spin1/2 kagome antiferromagnets Herbertsmithite and Zndoped 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 firstprinciples calculations for these proposed QSLs. Applying this method to a supercell containing CuZn 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 lowtemperature NMR data. 
Thursday, March 5, 2020 12:15PM  12:27PM 
S46.00004: Thermal conductivity of the quantum spin liquid candidate herbertsmithite Patrick BourgeoisHope, Pierre Lefloïc, Nicolas DoironLeyraud, Louis Taillefer, Philippe Mendels, Matias Velazquez Hosting a S = 1/2 system on a kagome lattice, herbertsmithite (ZnCu_{3}(OH)_{6}Cl_{2}) 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 lowenergy 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 Tlinear contribution to heat conduction that is expected from mobile spinons. Instead, our results suggest that the lowenergy 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 Ti^{3+} 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 Rb_{2}NaTi_{3}F_{12}, Cs_{2}NaTi_{3}F_{12}, and Cs_{2}KTi_{3}F_{12}. We determine magnetization curves in excellent agreement with experimental observations. Our calculations successfully clarify the relationship between the experimental observations and the magnetizationplateau 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, ChiaMin 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 firstprinciples 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 spinorbit 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 sitediluted Heisenberg antiferromagnetic on the kagome bilayer Preetha Saha, Depei Zhang, SeungHun Lee, GiaWei Chern We present spin dynamical simulations of the sitediluted Heisenberg antiferromagnet with nearest neighbor interactions on a quasi2D kagome bilayer. This geometrically frustrated lattice consists of two kagome layers connected by a triangularlattice 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 quasifree “orphan” spins leads to a distinctive long time powerlaw tail in the autocorrelation function. We discuss the implications of our work for the glassy behaviors observed in the frustrated magnet SrCr_{9p}Ga_{12−9p}O_{19}(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 spin1/2 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 spin1 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 manybody 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 Na_{2}Ti_{3}Cl_{8} 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 NaCaNi_{2}F_{7}. 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, YongLei Wang, WaiKwong Kwok, Lance Eric De Long Nanofabrication techniques allow magnetic thin films to be lithographically patterned into arrays of interacting macrospins 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 threefold 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. 

S46.00010: Tuning the Twostep 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 KosterlitzThouless (KT) phase. The two distinct melting processes are likely separated by a multicritical point identified in Ref.[2]. 

S46.00011: Noncoplanar magnetic order and topological magnons in tripod kagome antiferromagnet Yb_{3}Mg_{2}Sb_{3}O_{14} 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 spinorbit coupled rare earth ions. Using elastic neutron scattering measurements, we show that one of the tripod kagome compounds, Yb_{3}Mg_{2}Sb_{3}O_{14}, orders into a strongly noncoplanar 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 Yb_{3}Mg_{2}Sb_{3}O_{14 }as a candidate to host topological nontrivial magnon bands. 
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