Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session L24: 2D Frustrated Spin Systems: Triangular and KagomeFocus

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Sponsoring Units: GMAG DMP Chair: Sara Haravifard, Duke Univ Room: LACC 403A 
Wednesday, March 7, 2018 11:15AM  11:27AM 
L24.00001: Quantum fluctuations effects on the 1/3magnetization plateau of Ba_{3}CoSb_{2}O_{9} Jie Ma, Yoshitomo Kamiya, Luwei Ge, Tao Hong, Yiming Qiu, Diana L. Quintero Castro, Huibo Cao, Masaaki Matsuda, Cristian Batista, Martin Mourigal, Haidong Zhou Magnetization plateaux are emerged from the collective quantum phenomena in quantum magnets and have been the focus of intense research over the last decades. After analyzing the ground state of the triangular lattice S = 1/2 antiferromagnet Ba_{3}CoSb_{2}O_{9} at 0T, we investgate the dynamical properties of the 1/3 magnetization plateau phase under the magnetic field. By measuring the entire structure of the excitation spectrum and revealing excellent agreement with nonlinear spin wave theory, we demonstrate that magnons behave semiclassically in spite of the quantum origin of the underlying magnetic ordering. We also discuss implications of the present result to the elusive zerofield spin dynamics in the same material, which has been recently observed by different groups. 
Wednesday, March 7, 2018 11:27AM  11:39AM 
L24.00002: Magnetoelastic coupling in Ba_{3}CoSb_{2}O_{9} Ming Li, Guy Quirion, Martin Plumer, Jeffrey Quilliam, Haidong Zhou, Zhiling Dun In a variety of frustrated triangular lattice antiferromagnets (TLAF) with easyplane anisotropy, it has been shown that a magnetization plateau is produced at 1/3 of the saturation value for a magnetic field in the basal plane. This magnetization plateau is associated with a collinear upupdown state where two spins are parallel to the field while the third one is antiparallel. So far, this plateau has been shown to be accounted for by quantum and thermal fluctuations. In a classical model, quantum fluctuations can be taken into account using a biquadratic coupling (~S^{4}), responsible for the magnetization plateau in TLAF, which can also be associated with magnetoelastic effects. For triangular lattices with weak interlayer interaction and an effective 1/2 spin, Ba_{3}CoSb_{2}O_{9} is a frustrated quantum system. In order to determine the magnitude of biquadratic coupling, we estimated the magnetoelastic coupling strength by measuring the relative ultrasound velocity variation as a function of the field orientation at constant temperatures and field values. By analyzing the experimental results in paramagnetic and ordered states, which are significantly different, we can conclude that the magnetoelastic coupling in Ba_{3}CoSb_{2}O_{9} is large enough to stabilize the collinear upupdown state. 
Wednesday, March 7, 2018 11:39AM  11:51AM 
L24.00003: MerminWagner physics, (H,T) phase diagram, and candidate quantum spinliquid phase in the spin1/2 triangularlattice antiferromagnet Ba_{8}CoNb_{6}O_{24} Tao Xiang, Bruce Normand, Yi Cui, Jia Dai, Long Ma, Zheng Zhang, Shiyan Li, Graeme Luke, Weiqiang Yu Ba_{8}CoNb_{6}O_{24} presents a system whose Co^{2+} ions have an effective spin 1/2 and construct a regular triangularlattice antiferromagnet (TLAFM) with a very large interlayer spacing, ensuring purely twodimensional character. We exploit this ideal realization to perform a detailed experimental analysis of the S=1/2 TLAFM, which is one of the keystone models in frustrated quantum magnetism. We find strong lowenergy spin fluctuations and no magnetic ordering, but a diverging correlation length down to 0.1 K, indicating a MerminWagner trend towards zerotemperature order. Below 0.1 K, however, our lowfield measurements show an unexpected magnetically disordered state, which is a candidate quantum spin liquid. We establish the (H,T) phase diagram, mapping in detail the quantum fluctuation corrections to the available theoretical analysis. These include a strong upshift in field of the maximum ordering temperature, qualitative changes to both low and highfield phase boundaries, and an ordered regime apparently dominated by the collinear "upupdown" state. Ba_{8}CoNb_{6}O_{24} therefore offers fresh input for the development of theoretical approaches to the fieldinduced quantum phase transitions of the S=1/2 Heisenberg TLAFM. 
Wednesday, March 7, 2018 11:51AM  12:03PM 
L24.00004: Triangular lattice antiferromagnet CeCd_{3}As_{3} Sarah Dunsiger, Jeonghun Lee, Hyuna Park, Eundeok Mun CeCd_{3}As_{3} crystallizes into a hexagonal ScAl_{3}C_{3}type structure. The magnetic Ceions form the triangular lattice of the two dimensional layer. Thermodynamic and transport properties of CeCd_{3}As_{3} were investigated by measuring the magnetization, electrical resistivity, and specific heat. The Ceions in this metallic compound are well localized but do not order down to 0.42 K despite having a large negative Weiss temperature. In this presentation, anomalous physical properties due to the geometrical frustration of Ceions will be discussed. 
Wednesday, March 7, 2018 12:03PM  12:15PM 
L24.00005: Quantum Phase Diagram and Quantum Monte Carlo Study of the XYZ Spin Model: The Dipoleoctupole Doublets on a Triangular Lattice Zhihuan Dong, Zhiyu Dong, YiBin Yang, Xuefeng Zhang, Gang Chen Motivated by the recent activities on the geometrically frustrated rareearth magnets, we study the quantum phase diagram of the XYZ spin model that describes the dipoleoctupole doublets on a triangular lattice. Due to the absence of the sign problem of this model in a large parameter regime, we carry out the first quantum Monte Carlo calculation with the stochastic series expansion method and obtain the magnetic ground states with and without the external magnetic fields. The combination of the geometrical frustration and the anisotropic spin interaction leads to a rather rich phase diagram with a multitude of symmetry breaking orders. Moreover, the multipolar nature of the dipoleoctupole doublet brings new ingredients for the quantum fluctuations in the ordered phases. The experimental relevance to the rareearth triangular lattice materials is discussed. 
Wednesday, March 7, 2018 12:15PM  12:27PM 
L24.00006: Crystallization and vitrification of strongly correlated electrons on a geometrically frustrated triangular lattice Kenichiro Hashimoto, Satoru Sasaki, Ryota Kobayashi, Keisuke Itoh, Satoshi Iguchi, Yutaka Nishio, Yuka Ikemoto, Taro Moriwaki, Naoki Yoneyama, Masashi Watanabe, Akira Ueda, Hatsumi Mori, Kensuke Kobayashi, Reiji Kumai, Youichi Murakami, Jens Mueller, Takahiko Sasaki We report a unique glassy state of electrons – in contrast to longrange charge ordering (CO) – realized in the organic conductor θ_{m}(BEDTTTF)_{2}TlZn(SCN)_{4}, where the lack of periodicity of the strongly correlated electrons on the triangular lattice, characterizing the glassy state, is caused by geometric frustration and strong quantum effects [1]. Our experiments reveal that the CO transition (charge crystallization) can be avoided by rapid cooling, and charge vitrification occurs via a supercooled chargeliquid state. This is accompanied by heterogeneous slow dynamics, which in turn can be understood by the notion of the energy landscape with multiple local minima. We demonstrate that the crystallization of strongly correlated electrons involves the same nucleation and growth processes as that of conventional glassforming liquids such as structural and metallic glasses. These similarities among different classes of glass formers are surprising and will constitute further new insights to our general understanding of the liquidglass transition. 
Wednesday, March 7, 2018 12:27PM  12:39PM 
L24.00007: Large fieldinduced anomalous Hall effect in itinerant frustrated antiferromagnet PdCrO_{2} Jong Ok, Y. H. Kim, Y. J. Jo, Eun Choi, Jun Sung Kim PdCrO_{2} is one of the rare metallic triangularlattice antiferromagnets in the ultraclean limit. We report the observation of unusually large anomalous Hall (AH) effect in PdCrO_{2} induced by high magnetic field near T_{N}. The fieldinduced AH conductivity (σ_{xy}^{A}), measured in a highquality microstructured single crystal, is found to be exceptionally large as compared to magnetization (M), yielding the maximum AH factor S_{H} = σ_{xy}^{A}/M, two orders of magnitude larger than found in ferromagnets. Such an enhancement of S_{H} is observed in the intermediate temperature regime near T_{N}, but is suppressed either well below or above T_{N}. These findings demonstrate that scattering of highly mobile electrons of shortrange spin correlation among the frustrated spins can be an effective source on large AH effect. 
Wednesday, March 7, 2018 12:39PM  12:51PM 
L24.00008: Dynamical Structure Factor of Triangular Heisenberg Model Esteban Ghioldi, Matías Gabriel Gonzalez, Shangshun Zhang, Yoshitomo Kamiya, Luis O. Manuel, Adolfo E. Trumper, Cristian Batista We compute the zero temperature dynamical structure factor S(q,ω) of the triangular lattice Heisenberg model using a Schwinger Boson approach that includes the Gaussian fluctuations (1/N correction) of the saddle point solution. While the ground state of this model exhibits a wellknown 120 magnetic ordering, the excitation spectrum revealed by S(q,ω) has a strong quantum character, which is not captured by loworder 1/S expansions. The lowenergy energy magnons consist of two spinon bound states confined by the gauge fluctuations of the auxiliary field. This composite nature of the magnons leads to an internal structure of the magnon peaks. In addition, the continuum of highenergy spinon modes extends up to three times the singlemagnon bandwidth. 
Wednesday, March 7, 2018 12:51PM  1:03PM 
L24.00009: Highly mobile gapless excitations in a spin liquid state of 1TTaS_{2} Hinako Murayama, Yuki Sato, Xiangzhuo Xing, Tomoya Taniguchi, Shigeru Kasahara, Yuichi Kasahara, Masaro Yoshida, Yoshihiro Iwasa, Yuji Matsuda Quantum spin liquid (QSL) is a state of matter where strong quantum fluctuations destroy the longrange magnetic order even at zero temperature. In twodimensional triangular lattice antiferromagnet, such as organic insulators, possible QSL states have been reported. However, detailed properties remain unclear due to lattice distortion and strong spinorbit coupling. 
Wednesday, March 7, 2018 1:03PM  1:15PM 
L24.00010: Gapless Excitations in the Ground State of 1TTaS_{2} Amit Ribak, Itai Silber, Christopher Baines, Khanan Chashka, Zaher Salman, Yoram Dagan, Amit Kanigel 1TTaS_{2} is a layered transition metal dichalgeonide with a very rich phase diagram. At T=180K it undergoes a metal to Mott insulator transition. Mott insulators usually display antiferromagnetic ordering in the insulating phase but 1TTaS_{2} was never shown to order magnetically. We have shown that 1TTaS_{2} has a large paramagnetic contribution to the magnetic susceptibility but it does not show any sign of magnetic ordering or freezing down to 20mK, as probed by μSR, possibly indicating a quantum spin liquid ground state. Although 1TTaS_{2} exhibits a strong resistive behavior both in and outof plane at low temperatures we find a linear term in the heat capacity suggesting the existence of a Fermisurface, which has an anomalously strong magnetic field dependence. 
Wednesday, March 7, 2018 1:15PM  1:27PM 
L24.00011: Properties of the NonMagnetic Insulating Phase of the Triangular Lattice Hubbard Model from Density Matrix Renormalization Group Calculations Aaron Szasz, Johannes Motruk, Joel Moore Experimental studies have found signatures of a quantum spin liquid phase in organic crystals whose physics is believed to be described by the Hubbard model on the triangular lattice at half filling. Several theoretical studies, including with the density matrix renormalization group (DMRG) on finite systems, confirm the appearance of a possible spin liquid phase between the metallic and magnetically ordered phases of this model. However, the precise nature of the phase is still not completely clear. In this work, we use infinitesystem DMRG (iDMRG) on a cylinder geometry in a mixed real and momentumspace basis to further investigate the ground state phase diagram of the Hubbard model on the triangular lattice, with a focus on the purported spin liquid regime. iDMRG allows for calculation of additional quantities such as longrange correlation functions and logarithmic growth of the entanglement entropy that were not available in past numerical work; with these tools, we are able to provide a more complete description of the nonmagnetic insulating phase of the model. 
Wednesday, March 7, 2018 1:27PM  1:39PM 
L24.00012: Evidence for a Z2 topological ordered quantum spin liquid in a kagomelattice antiferromagnet Yuan Wei, Zili Feng, Clarina Dela Cruz, Wiebke Lohstroh, Wei Yi, Lei Shu, Jianlin Luo, JiaWei Mei, ZiYang Meng, Youguo Shi, Shiliang Li A quantum spin liquid with a Z2 topological order has long been thought to be important for the application of quantum computing and may be related to hightemperature superconductivity. While a twodimensional kagome antiferromagnet may host such a state, strong experimental evidence is still lacking. Here we show that Cu3Zn(OH)6FBr exhibits gapped spin continuum at low temperature and is not magnetically ordered down to 20 mili Kelvin. The spin triplet gap value is about twice of the spinon gap value reported previously. Our results provide firm ground for the existence of spin1/2 spinon excitations in Cu3Zn(OH)6FBr, whose ground state is thus a gapped quantum spin liquid with Z2 topological order. 
Wednesday, March 7, 2018 1:39PM  1:51PM 
L24.00013: Averievite: a spin1/2 copper oxide kagome antiferromagnet Antia Botana, Hong Zheng, John Mitchell, Michael Norman The synthesis of herbertsmithite has led to a revolution in the field of quantum magnetism. This Cu^{2+}hydroxide mineral constituted the first realization of the quantum spin liquid state in a spin1/2 system with kagome geometry, a long sought holy grail in Condensed Matter Physics. Ever since, other candidate materials have been intensively searched for. Herbertsmithite taught us that the conditions required for a quantum spin liquid to form are often found in Nature. Within this context, we have identified and synthesized averievite, an oxide mineral discovered in a volcano in the Kamchatka peninsula. Composed of Cu^{2+ }kagome layers sandwiched by Cu^{2+}V^{5+} honeycomb layers, partial substitution with Zn leads to spin liquid behavior, in analogy to herbertsmithite. 
Wednesday, March 7, 2018 1:51PM  2:03PM 
L24.00014: OrderbyDisorder in a Chiral Magnet on the Kagome Lattice Jackson Pitts, Kirill Shtengel Counting arguments alone are not sufficient to resolutely predict the orderbydisorder mechanism which drives coplanar ordering in the classical kagome Heisenberg antiferromagnet (KHAFM). The relationship between the dimension of the groundstate manifold as estimated by Maxwell counting and the number of softmodes in coplanar groundstates classifies the model as marginal according to the orderbydisorder criterion established by Moessner and Chalker (Phys. Rev. B 58, 12049 (1998). We have demonstrated that the classical model consisting of scalar spin chiralities on the kagome lattice (the "kagome chiral model") has the same groundstate degeneracy as estimated by Maxwell counting, and it has a subset of groundstates in close analogy to the coplanar groundstates favored by the KHAFM. However, this new model has fewer softmodes, and they populate a more restricted set of groundstates. We undertake Monte Carlo simulation to demonstrate that orderbydisorder in the kagome chiral model is more discriminating in its selection of states at low temperature. 
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