Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session C38: Spin Chains and 1D MagnetismFocus

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Sponsoring Units: GMAG Chair: Roberta Sessoli, University of Florence Room: BCEC 206B 
Monday, March 4, 2019 2:30PM  2:42PM 
C38.00001: Thermal evolution of quasionedimensional spin correlations within the anisotropic triangular lattice of αNaMnO_{2} Rebecca Dally, Robin Chisnell, Leland Harriger, Yaohua Liu, Jeffrey W Lynn, Stephen Wilson The temperature dependence of the magnetic order on the spatially anisotropic triangular lattice of αNaMnO_{2} will be presented. Single crystals were studied via timeofflight and tripleaxis neutron diffraction measurements, which revealed the transition into a commensurate, collinear antiferromagnetic ground state with k = (0.5, 0.5, 0) occurs below T_{N} = 22 K. Above this temperature, the transition is preceded by the formation of a coexisting, shortrange ordered, incommensurate state below T_{IC} = 45 K whose two dimensional propagation vector evolves toward k = (0.5, 0.5) as the temperature approaches T_{N}. At high temperatures (T > T_{IC}), quasielastic scattering reveals onedimensional spin correlations along the nearest neighbor MnMn "chain direction" of the MnO_{6} planes. Our data are consistent with the predictions of a mean field model of Isinglike spins on an anisotropic triangular lattice, as well as the predominantly onedimensional Heisenberg spin Hamiltonian reported for this material. 
Monday, March 4, 2019 2:42PM  2:54PM 
C38.00002: Thermal control of spin excitations in the coupled Isingchain material RbCoCl_{3} Christian Ruegg, Mattia Mena, Nora Haenni, Simon Ward, Eva Hirtenlechner, Robert Bewley, Claudius Hubig, Ulrich Joseph Schollwoeck, Bruce Normand, Karl Kraemer, Desmond F McMorrow We have used neutron spectroscopy to investigate the spin dynamics of the quantum (S = 1/2) antiferromagnetic Ising chains in RbCoCl_{3}. The structure and magnetic interactions in this material conspire to produce two magnetic phase transitions at low temperatures, presenting an ideal opportunity for thermal control of the chain environment. The highresolution spectra we measure of twodomainwall excitations therefore characterize precisely both the continuum response of isolated chains and the ``Zeemanladder'' bound states of chains in three different effective staggered fields in one and the same material. We apply an extended Matsubara formalism to obtain a quantitative description of the entire dataset, Monte Carlo simulations to model the magnetic order, and finitetemperature DMRG calculations to interpret the spectral features of all three phases, providing a complete understanding of the multifaceted Ising physics of RbCoCl_{3}. 
Monday, March 4, 2019 2:54PM  3:06PM 
C38.00003: Spin dynamics in quasionedimensional antiferromagnets Sylvain Capponi, Maxime Dupont, Edmond Orignac, Nicolas Laflorencie Theoretically challenging, the understanding of the dynamical response in quantum antiferromagnets is of great interest, in particular for both inelastic neutron scattering (INS) and nuclear magnetic resonance (NMR) experiments. In such a context, we theoretically address this question for quasionedimensional quantum magnets, e.g., weakly coupled spin chains for which many compounds are available in nature. In this class of systems, the dimensional crossover between a threedimensional ordered regime at low temperature towards onedimensional physics at higher temperature is a nontrivial issue, notably difficult concerning dynamical properties. We present a comprehensive theoretical study based on both analytical calculations and numerical simulations which allows us to describe the full temperature crossover for the NMR relaxation rate 1/T1 or the dynamical structure factor probed by INS, from onedimensional TomonagaLuttinger liquid physics to the threedimensional ordered regime, as a function of interchain couplings [1]. 
Monday, March 4, 2019 3:06PM  3:42PM 
C38.00004: Spin1/2 antiferromagnetic chiral chains: the sineGordon model and beyond. Invited Speaker: Paul Goddard The dramatic effect of an alternating local spin environment on the properties of the spin1/2 antiferromagnetic chain was first discovered through highfield neutron scattering and heat capacity experiments on copperbenzoate, which revealed the development of an energy gap on application of magnetic field. This was perplexing until it was found that the behaviour of this system, and a handful of others, could be described by the sineGordon model of quantumfield theory. Under the influence of the applied field, the gap emerges thanks to the presence of internal staggered fields and DM interactions that are a direct result of the staggered Cu(II) octahedra. 
Monday, March 4, 2019 3:42PM  3:54PM 
C38.00005: Formation of a Longitudinal Mode in One Dimensional Yb_{2}Pt_{2}Pb William Gannon, Igor Zaliznyak, Liusuo Wu, Alexei Tsvelik, Franz Demmel, Georg Ehlers, Andrei Podlesnyak, Meigan Aronson The low energy magnetic excitations measured with neutron scattering (NS) in Yb_{2}Pt_{2}Pb are spinons on one dimensional chains, in good agreement with the expectations of the XXZ Hamiltonian for nearly isotropic S=±1/2 magnetic moments despite the large, rare earth Yb^{3+ }moments that make up the system [1]. In applied magnetic field, we observe spinon confinement into bound states coinciding with a longitudinally polarized interchain mode [2]. New NS measurements probe the dispersion of this mode as a function of field in the vicinity of the confinement transition. We find weak modifications to the quantum continuum for fields approaching the critical field of 0.7 T, with the mode growing in intensity as field is increased through the transition. Interestingly, the antiferromagnetic order is strongly pinned with periodicity that does not evolve smoothly as a function of field as seen previously in a different orientation [2]. Rather, there is an abrupt transition to a weak, completely incommensurate order at 1.3 T with the mode correspondingly returning spectral weight to the continuum, reflecting strong low dimensional fluctuations even at fields near saturation. 
Monday, March 4, 2019 3:54PM  4:06PM 
C38.00006: Thermal fluctuation in low dimensional systems  an experimental, computational and analytical study Noam Kestin, Thierry Giamarchi

Monday, March 4, 2019 4:06PM  4:18PM 
C38.00007: Coercivity Dependence on Chain Length in a LowDimensional Magnetic System Thomas Gredig, Kevin Cano Single chain magnets deposited in the form of thin films can have tunable average chain lengths. A small molecule, iron phthalocyanine, is sublimed on a noninteracting substrate in the form of a thin film with a thickness of about 100 nm. The molecule's central ions form magnetic chains that are oriented parallel to the substrate surface. Furthermore, the average chain length is varied using the substrate deposition temperature in order to achieve a set of different magnetic responses as measured in magnetic hysteresis loops. The coercivity increases strongly with samples that have longer chain lengths. For comparison, a model with reduced dimensions based on single domain spherical magnetic particles in the superparamagnetic regime is developed and applied to this data set. The lowerdimensionality markedly extends the range of grain sizes over which the coercivity increases. 
Monday, March 4, 2019 4:18PM  4:30PM 
C38.00008: Normal Modes of a Spin Cycloid or Helix Randy Fishman, Toomas Room, Rogério de Sousa Although spin cycloids and helices are quite common, remarkably little is known about the normal modes of a spin cycloid or helix with finite length on a discrete lattice. Based on simple onedimensional lattice models, we numerically evaluate the normal modes of a spin cycloid or helix produced by either DzyalloshinskiiMoriya (DM) or competing exchange (CE) interactions. The normal modes depend on the type of interaction and on whether the nearestneighbor exchange is antiferromagnetic (AF) or ferromagnetic (FM). In the AF/DM and FM/DM cases, there is only a single Goldstone mode; in the AF/CE and FM/CE cases, there are three. For FM exchange, the spin oscillations produced by nonGoldstone modes contain a mixture of tangential and transverse components. For the DM cases, we compare our numerical results with analytic results in the continuum limit. 
Monday, March 4, 2019 4:30PM  4:42PM 
C38.00009: The dynamic structure factor in impuritydoped spin chains in a magnetic field Imke Schneider, Kevin Jägering, Annabelle Bohrdt, Sofia Brenner, Daniel Wessel, Sebastian Eggert

Monday, March 4, 2019 4:42PM  4:54PM 
C38.00010: Firstprinciples investigation of the complex lattice, charge, orbital, and spin structures in the spinel CuIr_{2}S_{4} Xilian Jin, Weiguo Yin The CuIr_{2}S_{4} thiospinel undergoes a metalinsulator transition at 230K on cooling accompanied by very large variations in the IrIr bond lengths and the loss of localized magnetic moments. This phenomenon has been interpreted in terms of a unique octamer model and orbitally driven onedimensional Peierls transition. Here we report systematic firstprinciples studies of the crystal structures, electronic band structures, and phonon spectra of CuIr_{2}S_{4}, as well as the effects of electronphonon, electronelectron, and spinorbit interactions. Wannier function analysis is used to derive the effective lowenergy Hamiltonian. Our results suggest a new way to understand this material. 
Monday, March 4, 2019 4:54PM  5:06PM 
C38.00011: New spinfiltering mechanism through atomic chains without magnetic field: firstprinciples study Tomonori Tanaka, Yoshihiro Gohda We investigated a new onedimensional (1D) Rashba system, Biadsorbed In atomic chains, using firstprinciples calculations. One of the most stable structures in the system shows unconventional spin textures, which is the reversal of the spin polarization direction in Rashba bands. This result suggests a new spinfiltering mechanism through atomic chains. Similar mechanisms to ours, 1D spin filter, have been proposed already. However, our mechanism has a great advantage; previous spinfiltering mechanisms require the external magnetic field, whereas ours does not need the magnetic field. This feature is suitable for spintronic applications. 
Monday, March 4, 2019 5:06PM  5:18PM 
C38.00012: Very slow spin dynamics in a ferromagnetic chain with threebody interactions Kevin Beach, Khagendra Adhikari Projector Monte Carlo methods can be adapted to quantum spin models in which the Hamiltonian is a sum of local threebody operators. I discuss the case of spinhalf chains whose interactions are pairwise ferromagnetic but contingent on the spin state at a third adjacent site. The resulting family of Hamiltonians, which includes the Fredkin spin chain and its tdeformed cousins, is frustrationfree but highly nontrivial. The phase diagram includes states with large entangelement and unusually slow dynamics. Since the Monte Carlo can be carried out independently within each spin sector, I am able to present numerical data for the ground state and various lowlying excitations. 
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