Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session V5: Frustrated Magnetism: Low Dimensional Magnets IIFocus

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Sponsoring Units: GMAG DMP Chair: Alexander Chernyshev, University of California, Irvine Room: 301 
Thursday, March 17, 2016 2:30PM  3:06PM 
V5.00001: Chiral spin liquids in arrays of spin chains Invited Speaker: Rodrigo Pereira The chiral spin liquid proposed by Kalmeyer and Laughlin is a spin analogue of the fractional quantum Hall effect: it has gapped bulk quasiparticles, chargeneutral chiral edge modes and topological order in the ground state. Recently there has been unambiguous numerical evidence that the chiral spin liquid can be stabilized as the ground state of extended Heisenberg models on the kagome lattice. I will talk about an analytical approach to investigate the emergence and the properties of the chiral spin liquid phase in spatially anisotropic 2D lattices. The approach is inspired by “coupledwire constructions” of quantum Hall states: starting from a quasi1D system, we build towards the 2D limit by coupling Heisenberg chains with threespin interactions that drive the chiral spin order. Using a renormalization group analysis, we show that the chiral spin liquid is more easily stabilized in the kagome lattice than in the triangular lattice. Moreover, using the conformal field theory that describes single chains, we explicitly construct the operators that create bulk quasiparticles and those that account for the topological degeneracy on the torus. I will also discuss possible extensions of this approach to construct more exotic quantum spin liquids. [Preview Abstract] 
Thursday, March 17, 2016 3:06PM  3:18PM 
V5.00002: Entanglement Entropy and Topological Order in Resonating ValenceBond Quantum Spin Liquids Julia Wildeboer, Alexander Seidel, Roger Melko On the triangular and kagome lattices, shortranged resonating valence bond (RVB) wave functions can be sampled without the sign problem using a recentlydeveloped Pfaffian Monte Carlo scheme [1]. In this talk [2], we present a study of the Renyi entanglement entropy in these wave functions using a replicatrick method [3]. Using various spatial bipartitions, including the LevinWen construction, our finitesize scaled Renyi entropy gives a topological contribution consistent with $\gamma = \text{ln}(2)$, as expected for a gapped $\mathbb{Z}_{2}$ quantum spin liquid. We prove that the mutual statistics are consistent with the toric code anyon model and rule out any other quasiparticle statistics such as the double semion model. \newline [1] J. Wildeboer and A. Seidel, PRL {\bf 109}, 147208 (2012). \newline [2] J. Wildeboer, A. Seidel, and R. G. Melko, submitted to PRL. \newline [3] M. B. Hastings, I. Gonzalez, A. B. Kallin, and R. G. Melko, PRL {\bf 104}, 157201 (2010). [Preview Abstract] 
Thursday, March 17, 2016 3:18PM  3:30PM 
V5.00003: A numerical study of the energy gap of the quantum dimerpentamer model Owen Myers, Chris Herdman We present a study of the energy gap in the quantum dimerpentamer model (QDPM) on the square lattice. This model is a generalization of the square lattice quantum dimer model (QDM), with a configuration space comprising fullypacked hardcore dimer coverings of the lattice, as well as configurations containing pentamers, where four dimers touch a vertex. Thus in the QDPM, the fullypacked, hardcore constraint of the QDM is relaxed such that the local dimer number at each vertex is fixed modulo 3; correspondingly, the local $U(1)$ gauge symmetry of the QDM Hilbert space is reduced to a local $Z_3$ gauge symmetry in the QDPM. Previous work has demonstrated the disordered quantum liquid nature of the ground state of the QDPM at the RokhsarKivelson point. Here we present a study of the energy gap above the ground state at the RK point, as computed via Monte Carlo from imaginary time correlations. To investigate the possibility of $Z_3$ topological order in this system, we study both the dimer density correlations as well as a $Z_3$ generalization of $Z_2$ vision correlations. Such vision correlations have previously been shown to display the nature of the low lying excitations in $Z_2$ topologically ordered QDMs. [Preview Abstract] 
Thursday, March 17, 2016 3:30PM  3:42PM 
V5.00004: A quantum spin liquid with a large topological degeneracy Oleg Tchernyshyov, Haoyu Wang, Yuan Wan We present a model of a quantum spin liquid in two dimensions with a large topological degeneracy. The model has spins of length $S=1/2$ on sites of a triangular lattice interacting via a 6spin term. As in models of Kitaev and Wen [13], elementary building blocks in our model are strings of several distinct types. Ends of these strings are elementary particles: 4 bosons and 3 fermions. Particles of different types are mutual semions. The degeneracy of the ground state on a torus is $2^{71} = 64$. Elementary excitations of the model are bosonfermion pairs, which come in $3 \times 4 = 12$ distinct types. [1] A. Kitaev, Ann. Phys. \textbf{303}, 2 (2003). [2] X.G. Wen, Phys.Rev.Lett. \textbf{90}, 016803 (2003). [3] A. Kitaev, Ann. Phys. \textbf{321}, 2 (2006). [Preview Abstract] 
Thursday, March 17, 2016 3:42PM  3:54PM 
V5.00005: Magnetic Frustration from Nonuniform $g$factors Weiguo Yin Frustrated magnets are commonly known as materials in which localized magnetic moments, or spins, interact through competing exchange interactions that cannot be simultaneously satisfied. Here we show that even when the exchange interactions are fully cooperative, magnetic frustration can be induced by nonuniform Land\'{e} $g$ factors, leading to a mutual interplay of typical ferromagnetic (FM) and antiferromagnetic (AF) features. This novel physicsexactly demonstrated in the onedimensional Ising model with alternating $g$ factors [1]provides new insight into the puzzling phenomenon that the magnetic susceptibility of many AF or FM materials is FMlike at low temperature but AFlike at high temperature. Furthermore, we found a unique magneticfielddriven quantum critical point at which one half of the spins are frozen into a complete order and the other half are fully disordered. The present theory joins the recent intensive search for frustrated magnets beyond the ``standard model'' of condensed matter physics. It could broaden our understanding and design of exotic magnetic behaviors such as spin ice, spin glass, and spin liquid that are essential to quantum computing, spintronics, and hightemperature superconductivity. [1] W.G. Yin and C. R. Roth, arXiv:1510.00030. [Preview Abstract] 
Thursday, March 17, 2016 3:54PM  4:06PM 
V5.00006: Quantum Spin Fluctuations and magnons in antiferromagnetically coupled bilayers with tuneable intrabilayer exchange  the case of Cr$_2$W(Te)O$_6$ Kingshuk Majumdar, S. D. Mahanti Recent neutron diffraction studies have shown that in Cr$_2$(W,Te)O$_6$ systems, which consist of bilayers with strong antiferromagnetic interbilayer coupling between Cr moments, the intrabilayer coupling between the Cr moments can be tuned from ferro (for W) to antiferro (for Te). Ab initio density functional calculations provide a microscopic understanding of the magnetic structure but cannot explain the magnitude of the ordered Cr$^{3+}$ moments. In order to understand the reduction of the ordered moment (ROM) caused by quantum spin fluctuations we have studied the magnon dispersion and ROM using a two parameter quantum Heisenberg spin Hamiltonian with tunable intra($j$) and antiferromagnetic inter ($J$) bilayer couplings. The magnon dispersion and sublattice magnetization have been calculated using nonlinear spin wave theory up to secondorder corrections in spin $S$. [Preview Abstract] 
Thursday, March 17, 2016 4:06PM  4:42PM 
V5.00007: Complex fieldinduced states in Linarite PbCuSO$_4$(OH)$_2$ with a variety of highorder exotic SDW$_p$ states Invited Speaker: Stefan S\"ullow Lowtemperature neutron diffraction and NMR studies of fieldinduced phases in linarite are presented for magnetic fields $H \ b$ axis. This way, we establish the magnetic phase diagram up to saturation. A twostep spinflop transition is observed as well as a transition transforming a helical magnetic ground state into an unusual magnetic phase with sinewave modulated moments $\ H$ enclosing all other magnetic phases in the $TH$ phase diagram. An effective $\tilde{J}_1\tilde{J}_2$ singlechain model with a magnetizationdependent frustration ratio $\alpha_{eff} =  \tilde{J}_1/\tilde{J}_2$ is proposed. The latter is governed by skew interchain couplings and shifted to the vicinity of the ferromagnetic critical point. It explains qualitatively the observation of a rich variety of exotic (for strongly correlated cuprate spin1/2 Heisenberg systems) longitudinal collinear spindensity wave SDW$_p$ states ($9 \geq p \geq 2$). [Preview Abstract] 
Thursday, March 17, 2016 4:42PM  4:54PM 
V5.00008: Largescale simulations of spindensitywave order in frustrated lattices Kipton Barros, Cristian Batista, GiaWei Chern We investigate spindensitywave (SDW) phases within a generalized meanfield approximation. This approach incorporates the thermal fluctuations of SDW order and the development of shortrange order above magnetic ordering temperatures $T_c$. Using a new Langevin dynamics method, we study mesoscale structures associated with triple$\mathbf Q$ SDW states that are induced by Fermi surface nesting in triangular and kagome lattice Hubbard models. The core of our linearscaling Langevin dynamics simulations is an efficient stochastic kernel polynomial method for computing the electron density matrix. We also investigate exotic phases above $T_c$ arising from preformed magnetic moments. [Preview Abstract] 
Thursday, March 17, 2016 4:54PM  5:06PM 
V5.00009: Electronic route to stabilize nanoscale spin textures in itinerant frustrated magnets Sanjeev Kumar, Sahinur Reja, Jeroen van den Brink We unveil novel spin textures in an itinerant fermion model on a frustrated triangular lattice in the limit of low electronic density. Using hybrid Monte Carlo simulations on finite clusters we identify two type of nanoscale spin textures in the background of 120$^{\circ}~$ order: (i) a planar ferromagnetic cluster, and (ii) and a noncoplanar cluster with spins oriented perpendicular to the 120$^{\circ}~$ plane. Both these textures lead to localization of the electronic wavefunctions and are inturn stabilized by the concomitant charge modulations. The noncoplanar spin texture is accompanied by an unusual scalar chirality pattern. A well defined electric charge and magnetic moment associated with these textures allow for their easy manipulation by external electric and magnetic fields  a desirable feature for data storage. We identify a localizationdelocalization behavior for electronic wavefunctions which is unique to frustrated magnets, and propose a general framework for stabilizing similar spin textures in spincharge coupled systems. [Preview Abstract] 
Thursday, March 17, 2016 5:06PM  5:18PM 
V5.00010: Stability and magnetization curve of spinnematic phase slightly below saturation field Hiroaki Ueda, Keisuke Totsuka We discuss the magnetization process slightly below the saturation field in frustrated magnets. A condensation of bound magnons on the spinpolarized state induces either a spin nematic phase or a state with phase separation. The (effective) interaction between the bound magnon pairs not only is crucial to the stability of the nematic phase, but also determines the slope of the magnetization curve near saturation. We generally derive the expression of this interaction by using the perturbative scattering theory. By applying the method to coupled zigzag chains LiCuVO4, we find the positive pairpair interaction implying the stability of the spin nematic phase. We also point out that the magnetization curve of LiCuVO4 is almost vertical (i.e. very large dM/dH) near the saturation exhibiting onedimensional feature despite nonnegligible interchain couplings. [Preview Abstract] 
Thursday, March 17, 2016 5:18PM  5:30PM 
V5.00011: Densitymatrix renormalization group study of triangular and square Hubbard models Shigetoshi Sota, Takami Tohyama, Tomonori Shirakawa, Seiji Yunoki We perform largescale densitymatrix renormalization group calculations for twodimensional Hubbard models with a triangular lattice and a square lattice [T. Tohyama, K. Tsutsui, M. Mori, S. Sota, and S. Yunoki, Phys. Rev. B \textbf{92}, 014515 (2015)]. In the triangular Hubbard model, we determined a boundary between metal and insulator and a boundary between spinliquid and antiferromagnetic phases. The presence of spinliquid phase is confirmed by spinspin correlation function. In the square Hubbard model, we introduce a secondneighbor hopping interaction and calculate the dynamical spin correlation function to clarify the doping dependence of magnon excitations. We find a shift of a peak position toward higher energy in the electrondoped side, being consistent with recent resonantinelastic xray scattering. [Preview Abstract] 
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