Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session A19: Spin Chains: ExperimentFocus

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Sponsoring Units: GMAG DMP Chair: Matthew Stone, Oak Ridge National Laboratory Room: LACC 308A 
Monday, March 5, 2018 8:00AM  8:12AM 
A19.00001: Quantum Criticality in a Strongly Coupled S=1 Spin Chain System at Ambient Field and Pressure Kirill Povarov, Alexandra Mannig, Gerard Perren, Johannes Möller, Erik Wulf, Jacques Ollivier, Andrey Zheludev We report spontaneous appearance of antiferromagnetic order in a model gapped quantum paramagnet Ni(Cl_{1x}Br_{x})_{2}4SC(NH_{2})_{2} induced by a change in bromine concentration x. The linear softmode spin waves, as well as magnetic Bragg peaks are observed directly in a Brrich material [1]. Comparison with the preceding studies on specimen with lower bromine concentration [2,3] allows us to reconstruct the overall phase diagram. The transition is qualitatively similar to a z=1 magnetic quantum critical point. However, the observed critical scaling of thermodynamic and magnetic properties has rather unusual critical exponents. 
Monday, March 5, 2018 8:12AM  8:24AM 
A19.00002: Tunable spinphonon scattering in lowD spin chain compounds AB_{2}O_{6} (A= Co, Ni; B= Sb, Ta) Narayan Prasai, Joshua Cohn, Aaron Christian, John Neumeier We report measurements of thermal conductivity (κ) in the range 5 K ≤ T ≤ 300 K for single crystals of the lowdimensional antiferromagnetic spinchain compounds CoSb_{2}O_{6}, NiSb_{2}O_{6}, CoTa_{2}O_{6} and NiTa_{2}O_{6}. While all of these compounds share the same tetragonal trirutile structure with space group P4_{2}/mnm, Co^{2+} has a spin3/2 and Ni^{2+} a spin1 state. The Ta compounds show a strongly suppressed κ over a broad range of temperature relative to the Sb compounds that is typically ascribed to resonant spinphonon scattering.^{a} We will discuss the possibility that this difference is caused by changes in the energy overlap of the magnon and phonon spectra associated with the Bsite ion substitution. 
Monday, March 5, 2018 8:24AM  8:36AM 
A19.00003: Molecular architecture and universalityclass control in S =1 quantum magnets^{§} Jamie Manson, John Singleton, Paul Goddard, Samantha DeAbreu, Jamie Brambleby, Will Blackmore, Rob Williams, Junjie Liu, Andrew Ozarowski, Danielle Villa, Cecelia Villa We have studied a large class of lowdimensional quantum magnets based on S = 1 Ni(II) ions. When coordinated to varying numbers of organic ligands and halides, we can observe all three universality classes; Heisenberg, Ising and XY. We show that the trend in the magnitude of the singleion anisotropy (D) coincides with predictions from the spectrochemical series. Also, it is found that NiX_{2}N_{4} coordination spheres (X = Br, I, NCS) have D < 0 (Isinglike) whereas X = Cl and F exhibit ground states with large, positive D (XYlike). Increasing the number of halide or oxygen donor atoms around the Ni(II) ion, to form NiX_{4}N_{2} or NiO_{4}N_{2}, induces an Isinglike ground state in the existing examples. In the absence of frustrated interactions, we demonstrate an ability to predict the orientation of the Ni(II) spin direction in simple systems, regardless of dimensionality or presence of longrange magnetic order, based solely on the singleion anisotropy. 
Monday, March 5, 2018 8:36AM  8:48AM 
A19.00004: Lowdimensional Quantum Magnetism in Cu(NCS)_{2}, a Molecular Framework Material Matthew Cliffe, Jeongjae Lee, Joseph Paddison, Sam Schott, Paromita Mukherjee, Michael Gaultois, Pascal Manuel, Henning Sirringhaus, Sian Dutton, Clare Grey Low dimensional magnetic materials with spin1/2 moments can host a range of exotic magnetic phenomena due to the intrinsic importance of quantum fluctuations to their behaviour. In this work we report the structure, magnetic structure and magnetic properties of copper(II) thiocyanate, Cu(NCS)2, a onedimensional coordination polymer which displays lowdimensional quantum magnetism. Magnetic susceptibility, electron paramagnetic resonance spectroscopy, ^{13}C magic angle spinning nuclear magnetic resonance spectroscopy, and density functional theory investigations indicate that Cu(NCS)_{2} behaves as a two dimensional array of weakly coupled antiferromagnetic spin chains (J_{2}=133(1)K, α=J_{1}/J_{2}=0.08). Powder neutron diffraction measurements confirm that below T_{N}=12 K Cu(NCS)_{2} orders as a commensurate Gtype antiferromagnet with a stronglyreduced ordered moment (0.3 μB) due to quantum fluctuations. 
Monday, March 5, 2018 8:48AM  9:00AM 
A19.00005: ^{63}CuNMR in pristine HKUST1 MOF: static and dynamic effects near the Cu environment Greta O'Dea, Guomeng Zhao, Engelbert Redel, Helmut Baumgart, Oscar Bernal NMR Spectroscopy is being used to explore magnetic and charge properties of the Cu(II)based metalorganic framework (MOF) HKUST1 and the change in conductivity that occurs between pristine HKUST1 and HKUST1 with tetracyanoquinodimethane (TCNQ) infiltration. The pulse NMR technique can be used to examine the interactions between the nuclei and the unpaired electrons in paramagnetic Cu(II) in pristine HKUST1. This will allow for further understanding of the effect on the conductivity of the material when the pores of the MOF are occupied by TCNQ. Here we report on the ^{63}CuNMR of pristine HKUST1. We find that the ^{63}CuNMR spectral linewidth in this system increases with decreasing temperature as would be expected for dipolar interactions of the paramagnetic Cu(II) ions with the nuclear moments. Surprisingly, we also find that the ^{63}Cu lineshift with respect to a CuBr reference is very close to that of copper metal. To shed light on this intriguing experimental result, we will present preliminary measurements of lineshape, spinlattice and spinspin relaxation times as functions of temperature and applied magnetic field in pristine HKUST1. 
Monday, March 5, 2018 9:00AM  9:12AM 
A19.00006: NBCT is an S = 1 antiferromagnetic nickel chain near the D/J quantum critical point Daniel Pajerowski, Jamie Manson, Mark Meisel, Andrei Podlesnyak, Timothy Prisk, Jacek Herbrych An S=1 antiferromagnetic chain, [Ni(HF2)(3Clpy)_{4}]BF_{4} (py = pyridine), henceforth NBCT, has been reported to be in the intermediate, inplane anisotropy limit, which is a region of phase space that has not been tested quantitatively against theoretical predictions (large D and small D have both been investigated thoroughly). The best fit Hamiltonian parameters for NBCT from magnetization and specific heat have the easyplane anisotropy D = 4.3 K, the intrachain antiferromagnetic interaction J = 4.86 K, and the interchain interaction J’ to be negligible, such that D/J = 0.88 in the vicinity of the D/J≈1 quantum critical point. Here, we present inelastic powder neutron scattering data that can be compared with density matrix renormalization group theory. 
Monday, March 5, 2018 9:12AM  9:24AM 
A19.00007: Study of quasione dimensional magnet Ti_{4}MnBi_{2} by neutron scattering Ping Miao, Abhishek Pandey, Hua He, Mason Klemm, Zhijun Xu, Yang Zhao, Jeffrey Lynn, Xiaofeng Qian, Meigan Aronson We report the investigation of magnetic structure of Ti_{4}MnBi_{2} that crystallizes into a tetragonal structure (space group: I 4/mcm, No. 140). The distance between two Mnions along the chain is relatively small (~2.5 A) while the distance between two adjacent chains is relatively large (~7.5 A), indicating the probable quasione dimensional magnetic character of the materials. T 
Monday, March 5, 2018 9:24AM  9:36AM 
A19.00008: Magnetic Properties of the New Low Dimensional Fluoride Compound NaCuF_{3} Fan Xiao, Karl Krämer, Christian Rüegg Experimental work on a physical realization of the Hubbard model NaCuF_{3} has been carried out inspired by recent theoretical calculation. Large quantities of NaCuF_{3} single crystals have been successfully synthesized and characterized. The experiments have suggested that rather than a singleband Hubbard model, this fluoride compound forms lowdimensional quantum Heisenberg system with the superexchange pathway going through cornersharing CuF6 octahedra and an exchange strength about 17 meV. Single crystal neutron diffraction experiments indicate a long range magnetic ordering at 18.85(1) K and excitation spectra revealed by recent inelastic neutron scattering experiment has shown a twospinon continuum at low temperature, characteristic of isolated antiferromagnetic Heisenberg spin chain. 
Monday, March 5, 2018 9:36AM  9:48AM 
A19.00009: Spinon confinement and fieldinduced transition in a quasionedimensional IsingHeisenberg antiferromagnet Shintaro Takayoshi, Shunsuke Furuya, Quentin Faure, Virginie Simonet, Sylvain Petit, Beatrice Grenier, Thierry Giamarchi We study a quasionedimensional antiferromagnet with Ising anisotropy. Lowenergy excitations in this system are spinons, which are confined by the interchain interaction and have a discrete excitation spectrum. We calculate the dynamical susceptibility considering interchain effects by a mean field theory. The result shows a discrete dispersion relation and agrees well with inelastic neutron scattering (INS) experiments on the compound BaCo_{2}V_{2}O_{8}. 
Monday, March 5, 2018 9:48AM  10:00AM 
A19.00010: THz Spectroscopy of the Quantum Criticality in a Transverse Field Ising Chain Compound CoNb_{2}O_{6} Johan Viirok, Dan Hüvonen, Toomas Room, Urmas Nagel, Christopher Morris, Seyed Koohpayeh, Tyrel McQueen, Peter Armitage, Jason Krizan, Robert Cava The onedimensional Ising chain in a transverse magnetic field is an ideal example of a system that undergoes an orderdisorder transition at a quantum critical point. The columbite CoNb_{2}O_{6} has been proposed as a good model system of the transverse field Ising chain allowing us to investigate the finitetemperature effects on quantum fluctuations near it’s quantum critical point. We studied the Ising chain material CoNb_{2}O_{6} using THz spectroscopy in high magnetic fields up to 17T and down to 0.1K. The system shows a softening of the spectrum as one approaches the quantum critical point at about 5.5T from the ferromagnetic side. This collapse of energy scales is compared to predictions for quantum criticality in the 1D Ising model tuned by transverse field. 
Monday, March 5, 2018 10:00AM  10:12AM 
A19.00011: Magnetic and thermal properties of a Haldane chain with onedimensional ferromagnetic chains in square lattice Joon Han Lee, Marie Kratochvílová, ZahraSadat Yamani, Dae Hwan Park, Hong Eun Choi, JeGuen Park, Yoon Seok Oh Since Haldane conjectured that ground state of onedimensional Heisenberg antiferromagnet has a finite spin gap for integer spins, while gapless excitations for halfodd integer spins, it has inspired lots of theoretical and experimental studies on lowdimensional quantum magnets. Several onedimensional chain systems of integer spins, so called Haldane chain, have been discovered and studied, such as CsNiCl_{3}, Y_{2}BaNiO_{5}, PbNi_{2}V_{2}O_{8}, SrNi_{2}V_{2}O_{8}, AgVP_{2}S_{6}. It has been known that most of the Haldane chain has antiferromagnetic coupling for the intrachain exchange interaction. Recently, we have found a Haldane chain compound in which antiferromagnetic order is accompanied by antiferromagnetic interchain coupling between onedimensional ferromagnetic chains below 30.5 Kelvin. In this presentation, we present comprehensive study of its magnetic and thermal properties. 
Monday, March 5, 2018 10:12AM  10:24AM 
A19.00012: Magnetic and structural properties of ultrashort 1D ferromagnetic chains Nicolas Vargas, Carlos Monton, Ivan Schuller The magnetic properties of 1D Fe and varying composition Fe/Co chains are studied as a function of chain length and structural composition. Ultrashort chains, ~7 to 400 atoms long, can be grown by organic molecular beam epitaxy using MetalloPhthalocyanine (MPc) superlattices (SLs). The orientation of the chains can be controlled by the appropriate choice of substrate whereas their length and composition can be controlled by the SL structure. Furthermore, the magnetic signal of ultrashort chains can be amplified by increasing the periodicity of the SL, which enables the use of conventional techniques such as VSM and SQUID to study their magnetic properties. In this work, we discuss the magnetic behavior of ultrashort 1D Fe chains as a function of length and composition. We have found that the coercive field decreases when the length of the chains is reduced from 400 to 7 atoms long. We correlate the observed magnetic behavior with structural information obtained from xray diffraction and refinement. 
Monday, March 5, 2018 10:24AM  10:36AM 
A19.00013: Spinon Confinement and a Longitudinal Mode in One Dimensional Yb_{2}Pt_{2}Pb William Gannon, Liusuo Wu, Igor Zaliznyak, Alexei Tsvelik, Franz Demmel, Meigan Aronson The Yb^{3+} magnetic moments in Yb_{2}Pt_{2}Pb are seemingly classical, since the large spinorbit coupling of the 4felectrons and the crystal electric field dictate a J = +/7/2 Yb ground state doublet. Surprisingly, the fundamental low energy magnetic excitations in Yb_{2}Pt_{2}Pb are spinons on one dimensional chains, shown to be in good agreement with the behavior expected with the XXZ Hamiltonian for nearly isotropic, S = +/1/2 magnetic moments. We have performed new high resolution neutron scattering measurements to examine the properties of these excitations in a magnetic field. In fields larger than 0.5 T, the chemical potential closes the gap to the spinon dispersion, modifying the quantum continuum through the formation of a spinon Fermi surface. This leads to the formation of spinon bound states along the chains, coupled to a longitudinally polarized interchain mode at energies below the quantum continuum. The ground state doublet nature of the Yb ions ensures that at all fields, transverse excitations are virtually nonexistent, giving unprecedented access to only the longitudinal excitation channel without the presence of spin waves or other transverse damping mechanisms, allowing direct measurement of the mode dispersion. 
Monday, March 5, 2018 10:36AM  10:48AM 
A19.00014: Spincharge separation probed with resonant inelastic xray scattering on doped onedimensional antiferromagnets Umesh Kumar, Alberto Nocera, Elbio Dagotto, Steven Johnston We propose a new method to observe spincharge separation and other exotic excitations in doped Sr_{2}CuO_{3} using the resonant inelastic xray scattering (RIXS) technique, which can simultaneously probe charge and spin degrees of freedom. Sr_{2}CuO_{3} hosts cornershared CuO_{3} plaquettes, in which the Cu spin moment1/2 couples antiferromagnetically along a onedimensional (1D) chain. Importantly, the spinchain can be doped with Co, Ni or Zn. We model the spinchain by exactly diagonalizing the 1D tJ Hamiltonian to study low energy spin and charge excitations of the doped system and provide predictions of the RIXS spectra at the oxygen Kedge for doped Sr2CuO3. Our results show that the RIXS spectra are rich, containing distinct two and fourspinon excitations, dispersive antiholon excitations, and combinations thereof. We also study dynamical spin and charge structure factors using DMRG which complements the RIXS spectra and helps to identify the spin and charge excitations. 
Monday, March 5, 2018 10:48AM  11:00AM 
A19.00015: Gapless Quantum Spin Liquid of the KagomeLattice Antiferromagnet Toru Sakai, Hiroki Nakano The S=1/2 kagomelattice antiferromagnet is one of interesting frustrated quantum spin systems. The spin gap is an important physical quantity to characterize the spin fluid behavior. Whether the S=1/2 kagomelattice antiferromagnet is gapless or has a finite spin gap, is still unsolved issue. Because any recently developped numerical calculation methods are not enough to determine it in the thermodynamic limit. Our largescale numerical diazonalization up to 42spin clusters and a finitesize scaling analysis indicated that the S=1/2 kagomelattice antiferromagnet is gapless in the thremodynamic limit[1]. It is consistent with the U(1) Dirac spin liquid theory of the kagomelattice antiferromagnet. On the other hand, the density matrix renormalization group calculations supported the gapped Z2 topological spin liquid theory. We propose one of better methods to determine whether the spin excitation is gapless or gapped, based on the finitesize scaling analysis of the spin susceptibility calculated by the numerical diagonalization. The present work indicates that the kagomelattice antiferromagnet is gapless[2]. 
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