Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
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 1/3-magnetization plateau of Ba3CoSb2O9 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 Ba3CoSb2O9 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 zero-field 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 Ba3CoSb2O9 Ming Li, Guy Quirion, Martin Plumer, Jeffrey Quilliam, Haidong Zhou, Zhiling Dun In a variety of frustrated triangular lattice antiferromagnets (TLAF) with easy-plane 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 up-up-down 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 bi-quadratic coupling (~S4), 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, Ba3CoSb2O9 is a frustrated quantum system. In order to determine the magnitude of bi-quadratic 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 Ba3CoSb2O9 is large enough to stabilize the collinear up-up-down state. |
Wednesday, March 7, 2018 11:39AM - 11:51AM |
L24.00003: Mermin-Wagner physics, (H,T) phase diagram, and candidate quantum spin-liquid phase in the spin-1/2 triangular-lattice antiferromagnet Ba8CoNb6O24 Tao Xiang, Bruce Normand, Yi Cui, Jia Dai, Long Ma, Zheng Zhang, Shiyan Li, Graeme Luke, Weiqiang Yu Ba8CoNb6O24 presents a system whose Co2+ ions have an effective spin 1/2 and construct a regular triangular-lattice antiferromagnet (TLAFM) with a very large interlayer spacing, ensuring purely two-dimensional 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 low-energy spin fluctuations and no magnetic ordering, but a diverging correlation length down to 0.1 K, indicating a Mermin-Wagner trend towards zero-temperature order. Below 0.1 K, however, our low-field 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 high-field phase boundaries, and an ordered regime apparently dominated by the collinear "up-up-down" state. Ba8CoNb6O24 therefore offers fresh input for the development of theoretical approaches to the field-induced quantum phase transitions of the S=1/2 Heisenberg TLAFM. |
Wednesday, March 7, 2018 11:51AM - 12:03PM |
L24.00004: Triangular lattice antiferromagnet CeCd3As3 Sarah Dunsiger, Jeonghun Lee, Hyuna Park, Eundeok Mun CeCd3As3 crystallizes into a hexagonal ScAl3C3-type structure. The magnetic Ce-ions form the triangular lattice of the two dimensional layer. Thermodynamic and transport properties of CeCd3As3 were investigated by measuring the magnetization, electrical resistivity, and specific heat. The Ce-ions 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 Ce-ions 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 Dipole-octupole Doublets on a Triangular Lattice Zhihuan Dong, Zhiyu Dong, Yi-Bin Yang, Xuefeng Zhang, Gang Chen Motivated by the recent activities on the geometrically frustrated rare-earth magnets, we study the quantum phase diagram of the XYZ spin model that describes the dipole-octupole 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 dipole-octupole doublet brings new ingredients for the quantum fluctuations in the ordered phases. The experimental relevance to the rare-earth 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 long-range charge ordering (CO) – realized in the organic conductor θm-(BEDT-TTF)2TlZn(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 charge-liquid 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 glass-forming 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 liquid-glass transition. |
Wednesday, March 7, 2018 12:27PM - 12:39PM |
L24.00007: Large field-induced anomalous Hall effect in itinerant frustrated antiferromagnet PdCrO2 Jong Ok, Y. H. Kim, Y. J. Jo, Eun Choi, Jun Sung Kim PdCrO2 is one of the rare metallic triangular-lattice antiferromagnets in the ultraclean limit. We report the observation of unusually large anomalous Hall (AH) effect in PdCrO2 induced by high magnetic field near TN. The field-induced AH conductivity (σxyA), measured in a high-quality micro-structured single crystal, is found to be exceptionally large as compared to magnetization (M), yielding the maximum AH factor SH = σxyA/M, two orders of magnitude larger than found in ferromagnets. Such an enhancement of SH is observed in the intermediate temperature regime near TN, but is suppressed either well below or above TN. These findings demonstrate that scattering of highly mobile electrons of short-range 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 well-known 120 magnetic ordering, the excitation spectrum revealed by S(q,ω) has a strong quantum character, which is not captured by low-order 1/S expansions. The low-energy 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 high-energy spinon modes extends up to three times the single-magnon bandwidth. |
Wednesday, March 7, 2018 12:51PM - 1:03PM |
L24.00009: Highly mobile gapless excitations in a spin liquid state of 1T-TaS2 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 long-range magnetic order even at zero temperature. In two-dimensional triangular lattice antiferromagnet, such as organic insulators, possible QSL states have been reported. However, detailed properties remain unclear due to lattice distortion and strong spin-orbit coupling. |
Wednesday, March 7, 2018 1:03PM - 1:15PM |
L24.00010: Gapless Excitations in the Ground State of 1T-TaS2 Amit Ribak, Itai Silber, Christopher Baines, Khanan Chashka, Zaher Salman, Yoram Dagan, Amit Kanigel 1T-TaS2 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 anti-ferromagnetic ordering in the insulating phase but 1T-TaS2 was never shown to order magnetically. We have shown that 1T-TaS2 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 1T-TaS2 exhibits a strong resistive behavior both in and out-of plane at low temperatures we find a linear term in the heat capacity suggesting the existence of a Fermi-surface, which has an anomalously strong magnetic field dependence. |
Wednesday, March 7, 2018 1:15PM - 1:27PM |
L24.00011: Properties of the Non-Magnetic 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 infinite-system DMRG (iDMRG) on a cylinder geometry in a mixed real- and momentum-space 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 long-range 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 non-magnetic 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 kagome-lattice antiferromagnet Yuan Wei, Zili Feng, Clarina Dela Cruz, Wiebke Lohstroh, Wei Yi, Lei Shu, Jianlin Luo, Jia-Wei 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 high-temperature superconductivity. While a two-dimensional 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 spin-1/2 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 spin-1/2 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 Cu2+-hydroxide mineral constituted the first realization of the quantum spin liquid state in a spin-1/2 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 Cu2+ kagome layers sandwiched by Cu2+-V5+ 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: Order-by-Disorder in a Chiral Magnet on the Kagome Lattice Jackson Pitts, Kirill Shtengel Counting arguments alone are not sufficient to resolutely predict the order-by-disorder mechanism which drives coplanar ordering in the classical kagome Heisenberg antiferromagnet (KHAFM). The relationship between the dimension of the ground-state manifold as estimated by Maxwell counting and the number of soft-modes in coplanar ground-states classifies the model as marginal according to the order-by-disorder 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 ground-state degeneracy as estimated by Maxwell counting, and it has a subset of ground-states in close analogy to the coplanar ground-states favored by the KHAFM. However, this new model has fewer soft-modes, and they populate a more restricted set of ground-states. We undertake Monte Carlo simulation to demonstrate that order-by-disorder in the kagome chiral model is more discriminating in its selection of states at low temperature. |
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