Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session G31: Focus Session: Spin Chains I: Random, Spin Peierls, and Uniform 
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Sponsoring Units: GMAG DMP Chair: Thierry Giamarchi, University of Geneva Room: 207A 
Tuesday, March 3, 2015 11:15AM  11:27AM 
G31.00001: Emergent SU(3) symmetry in random spin1 chains Victor Quito, Jose Hoyos, Eduardo Miranda We propose a system that realizes the idea of an ``emergent symmetry'': its lowtemperature behavior has a larger symmetry than the underlying Hamiltonian. This is found in generic SU(2)invariant random spin1 chains, whose complete phase diagram we mapped out and characterized both analytically and numerically. The system is shown to have two different lowtemperature phases with emergent SU(3) symmetry. In each of them, susceptibilities and correlation functions of both spin and quadrupolar operators are characterized by the same asymptotic exponents, which are dictated by the emergent symmetry group. Both SU(3)symmetric phases are governed by infinitely disordered ground states. Whereas one of the ground states is formed by random singlets of pairs of spins, the other is less conventional and consists of randomsinglet spin trios. [Preview Abstract] 
Tuesday, March 3, 2015 11:27AM  11:39AM 
G31.00002: Effects of magnetic site disorder of the 1D Ising spin chain compounds Ca$_{3}$(Co,Mn)$_{2}$O$_{6}$ with dilute doping Brian Casas, Paula Lampen, ManhHuong Phan, Hariharan Srikanth, Jozef Kovak, Ivan Skorvanek The spin chain compound Ca$_{\mathrm{3}}$Co$_{\mathrm{2}}$O$_{\mathrm{6}}$ has been extensively studied due to a number of unusual properties originating from geometrically frustrated Isinglike spin chains arranged in a triangular lattice. These quasi one dimensional structures provide an ideal environment to study dilute magnetic disorder in spinglass like systems. Disorder controlled via chemical doping has been observed to weaken the spin glass behavior and disrupt a number of metamagnetic transitions found in pristine Ca$_{\mathrm{3}}$Co$_{\mathrm{2}}$O$_{\mathrm{6}}$. We report a systematic study of the effects of dilute Mn doping ($x \quad =$ 0.05  0.50) in Ca$_{\mathrm{3}}$Co$_{\mathrm{2x}}$Mn$_{\mathrm{x}}$O$_{\mathrm{6}}$ synthesized via a solgel method. Detailed AC and DC magnetization measurements performed on a SQUID magnetometer reveal the suppression of the steplike metamagnetic transitions by a doping of $x \quad =$ 0.25. The relaxation time is found to decrease with increasing Mn content, showing the destruction of the spinglass like behavior. Our observations yield new insight into the role of site disorder on the glassy behavior in spin chain systems. [Preview Abstract] 
Tuesday, March 3, 2015 11:39AM  11:51AM 
G31.00003: Neutron scattering studies of a bonddisordered $S=1$ quantum spin liquid Kirill Povarov, Erik Wulf, Dan H\"{u}vonen, Severian Gvasaliya, Eric Ressouche, Jacques Ollivier, Armando PaduanFilho, Andrey Zheludev We report the results of the neutron scattering studies of a bonddisordered modification of a wellknown gapped $S=1$ antiferromagnetic quantum system NiCl$_{2}\cdot$4SC(NH$_{2}$)$_{2}$ (commonly referred to as DTN). The focus of the study is a zerofield spinliquid phase of a compound with 6\% of Cl to Br substitution. Inelastic neutron timeofflight measurements at a temperature of 60~mK were employed to map the magnetic excitation spectrum over the whole Brillouin zone with a high resolution. In addition, we have also investigated the critical properties of the fieldinduced phase transition in DTN specimen with various concentration of Br by means of neutron diffraction [1]. We compare these experimental results to the bulk measurements on DTN with similar levels of Cl/Br substitution and recent theoretical predictions for disordered quantum magnets.\\[4pt] [1] E. Wulf, D. H\"{u}vonen et al.; Phys. Rev. B \textbf{88}, 174418 (2013) [Preview Abstract] 
Tuesday, March 3, 2015 11:51AM  12:27PM 
G31.00004: Quasionedimensional spin nematic states and their excitations Invited Speaker: Oleg Starykh Much of the research in frustrated quantum magnets has focused on the elusive quest for magnetically disordered phases with highly entangled ground states  quantum spin liquids. Somewhat intermediate between these rare beasts and commonplace antiferromagnets are moderately exotic phases of antiferromagnets in strong magnetic fields which exhibit no dipolar magnetic order transverse to the field, contrary to typical spinflop antiferromagnetic states. I describe excitation spectra and dynamical response functions of two such phases  collinear spindensity wave and spin nematic. Both of these unusual phases are characterized by the presence of a gap to $S^z = \pm 1$ excitations, but differ qualitatively in details of lowenergy longitudinal (density like) response. I conclude the talk by describing high relevance of these two phases to the kagome antiferromagnet Volborthite. [Preview Abstract] 
Tuesday, March 3, 2015 12:27PM  12:39PM 
G31.00005: Competing orders of a magnetic impurity lattice in a onedimensional Fermi gas Michael Schecter, Mark Rudner, Karsten Flensberg We investigate the magnetic order of a classical spin chain interacting via a local exchange with onedimensional free fermions. Within a variational ansatz for the ordering spinfield, we find the exact phase boundaries between competing (anti)ferromagnetic and spiral orders as a function of the local exchange coupling strength and interimpurity spacing. The analysis applies for arbitrary coupling strength, and demonstrates that a rich variety of competing ground states is possible even at weak exchange coupling. Thus our results go beyond the frequently discussed RKKY limit where spiral order is preferred. We discuss various implications of our results in relation to recent work on producing topological states using magnetic adatoms on superconducting metals. [Preview Abstract] 
Tuesday, March 3, 2015 12:39PM  12:51PM 
G31.00006: Altering TCNQTCNQ interactions and a study of the spinPeierls state including muonfluorine entanglement Adam Berlie, Ian Terry, Sean Giblin, Marek Szablewski Potassium TCNQ is a well known spinPeierls system where a spin gap opens at ~390 K due to the strong electronphonon coupling within the material, essentially forming 1D stack of antiferromagnetially coupled anion TCNQ dimers. We show that on substitution of TCNQF$_4$ for the TCNQ this changes the interaction of the anions and shifts $T_{\rm sp}$ to ~150 K. Additionally, substitution of TCNQ by TCNQBr$_2$ produces a sample with an even lower interaction strength. These observations demonstrate the ability to tune this system from a chemical point of view. Muon spin relaxation measurements show that in the vicinity of $T_{\rm sp}$ the system is dominated by magnetic fluctuations and these persist to lower temperatures until the moments exhibit a quasistatic state on the time scale of the $\mu$SR experiment (MHz range). Within the KTCNQF4 sample we also observe the emergence of a small contribution from an entangled F$\mu^{+}$F where the data could be modeled using two environments that can help suggest possible muon stopping sites. [Preview Abstract] 
Tuesday, March 3, 2015 12:51PM  1:03PM 
G31.00007: Direct measurement of the spin gap in a quasionedimensional clinopyroxene: NaTiSi$_2$O$_6$ Harlyn Silverstein, Haidong Zhou, Johan van Lierop, Christopher Wiebe True inorganic SpinPeierls materials are rare, but NaTiSi$_2$O$_6$ was at one time considered an ideal candidate due to it having well separated chains of edgesharing TiO$_6$ octahedra. At low temperatures, this material undergoes a phase transition from \textit{C}2/c to \textit{P}$\bar{1}$\ symmetry, where trivalent TiTi dimers begin to form within the chains. However, it was quickly realized with magnetic susceptibility that simple spin fluctuations do not progress to the point of enabling such a transition. Since then, considerable experimental and theoretical endeavours have been taken to find the true ground state of this system and explain how it manifests. Here, we employ the use of xray diffraction, neutron spectroscopy, and magnetic susceptibility to directly and simultaneously measure the symmetry loss, spin singlettriple gap, and phonon modes. A gap of 53(3) meV was observed, fit to the magnetic susceptibility, and compared to previous theoretical models to unambiguously assign NaTiSi$_2$O$_6$ as having an orbitalassisted SpinPeierls ground state. [Preview Abstract] 

G31.00008: ABSTRACT WITHDRAWN 
Tuesday, March 3, 2015 1:15PM  1:27PM 
G31.00009: $Z_3$ symmetryprotected topological phases in SU(3) AKLT model Takahiro Morimoto, Hiroshi Ueda, Tsutomu Momoi, Akira Furusaki We study $Z_3$ symmetryprotected topological (SPT) phases in onedimensional systems with $Z_3 \times Z_3$ symmetry. We construct MPS wavefunctions for $Z_3$ SPT phases by using nontrivial cocycles of the group cohomology $H^2(Z_3\times Z_3,U(1)) = Z_3$. Their parent Hamiltonian turns out to be an SU(3) version of the AKLT model consisting of bilinear and biquadratic terms of su(3) operators in the ${\bf 8}$ representation. We apply iDMRG method to the SU(3) bilinearbiquadratic model of general coupling constants. We determine its phase diagram in which the nontrivial $Z_3$ SPT phase is present for a parameter range including the point of vanishing biquadratic term as well as the SU(3) AKLT point. We find a continuous phase transition from the $Z_3$ SPT phase to an SU(3) dimer phase, where we obtain a central charge $c=16/5$ from a scaling of the entanglement entropy. We also discuss that an $S=1$ spin chain with staggered quadrupole couplings reduces to the SU(3) AKLT model in the strong coupling limit. [Preview Abstract] 
Tuesday, March 3, 2015 1:27PM  1:39PM 
G31.00010: Symmetry fractionalization in SU(2n) antiferromagnetic Heisenberg chains Andreas Weichselbaum, Thomas Quella We explore generalizations of the AffleckKennedyLiebTasaki (AKLT, 1987) model for spin1 antiferromagnetic Heisenberg chains to higherrank SU(2n) symmetries. In particular we show that by proper tuning of higher order spin interactions there also exist exact lowdimensional matrixproduct ground states with fractionalized edge states, and that these states are adiabatically connected to the ground state of the plain SU(2n) Heisenberg model. The parameter space is explored using state of the art density matrix renormalization group (DMRG), explicitly utilizing SU(N) symmetry up to N=6 based on the QSpace tensor library. [Preview Abstract] 
Tuesday, March 3, 2015 1:39PM  1:51PM 
G31.00011: Unusual Magnetic Response of an S = 1 Antiferromagetic LinearChain Material. J.S. Xia, M.W. Meisel, A. Ozarowski, P.M. Spurgeon, A.G. Graham, J.L. Manson An $S = 1$ antiferromagnetic polymeric chain, [Ni(HF$_2$)(3Clpy)$_4$]BF$_4$ (py = pyridine), has been identified to have nearestneighbor antiferromagnetic interaction $J/k_B = 4.86$~K and singleion anisotropy $D/k_B = 4.3$~K, while avoiding longrange order down to 25~mK.\footnote{J.L.~Manson \emph{et al.}, Inorg.~Chem.~{\bf 51} (2012) 7520.} With $D/J = 0.88$, this system is close to the $D/J \approx 1$ gapless quantum critical point between the topologically distinct Haldane and Large$D$ phases. The magnetization was studied over a range of temperatures, 50~mK $\leq T \leq 1$~K, and magnetic fields, $B \leq 10$~T. The results allow an upper bound of the critical field, $B_c$, which closes the Haldane gap, to be estimated. Specifically, $B_c \leq (35 \pm 10)$~mT, which is close to the predicted 46~mT,\footnote{S.~Hu \emph{et al.}, Phys.~Rev.~B {\bf 84} (2011) 220402.} when using the reported$^2$ values of $J$, $D$, and $g$. In low fields, the magnetic signal increases with decreasing $T$ for 400~mK $< T < 800$~mK but is independent of $T$ for 50~mK $\leq T \leq 400$~mK. This observation is consistent with a significant increase in the specific heat arising from the accumulation of entropy in the vicinity of the quantum critical point. [Preview Abstract] 
Tuesday, March 3, 2015 1:51PM  2:03PM 
G31.00012: Evolution of Spinons with Magnetic Field in the OneDimensional Heavy Fermion Yb$_2$Pt$_2$Pb W.J. Gannon, L. Wu, I.A. Zaliznyak, F. Demmel, M.C. Aronson The antiferromagnetic (AF) metal Yb$_2$Pt$_2$Pb has a layered crystal structure, with Yb ions arranged in chains along the $c$axis, while pairs of chains form orthogonal dimers in the tetragonal $a$$b$ plane, an inplane structure that is topologically equivalent to the ShastrySutherland lattice (SSL). In zero magnetic field, 70\% of the magnetic spectral weight is static, consisting of AF Bragg peaks corresponding to moments that order at $T_N=2.07$ K, while fluctuations of the Yb moments, present even at T=0 are responsible for the remaining 30\%. The low energy magnetic excitation spectrum observed in neutron scattering experiments is unambiguously onedimensional, consisting exclusively of gapped, Heisenberglike spinons that disperse along the Yb chain direction, while remaining dispersionless in the SSL layers. As field is increased, the static magnetic order is suppressed and a rapidly evolving set of longitudinal modes with dispersions both parallel and perpendicular to the Yb chains is observed, until the Yb moments are fully polarized at fields above 2.3 T. This places Yb$_2$Pt$_2$Pb very near but on the ordered side of the quantum critical point that links quantum mechanical Heisenberg and classical Ising physics in one dimension. [Preview Abstract] 
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