Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session V24: Low Dimensional Spin Systems, NematicityFocus

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Sponsoring Units: GMAG DMP Chair: Marcelo Jaime, Los Alamos Natl Lab Room: LACC 403A 
Thursday, March 8, 2018 2:30PM  3:06PM 
V24.00001: Abstract Withdrawn Invited Speaker:

Thursday, March 8, 2018 3:06PM  3:18PM 
V24.00002: Theory of electron spin resonance for detecting longrange spin nematic orders Shunsuke Furuya, Tsutomu Momoi The spin nematic phase is an interesting quantum magnetic phase where the bound magnon pair condenses. One of the most important issues around the topic of the spin nematic phase is how to detect the spin nematic order experimentally. Many theoretical proposals were made to resolve that issue. In particular, the inelastic neutron scattering cross section turned out to be an appropriate way of detecting the spin nematic order under the weak magnetic field [1]. On the other hand, since the spin nematic phase often emerges under the strong magnetic field, a methodology for detecting the spin nematic phase under strong fields is still strongly called for. In this presentation, we discuss that the electron spin resonance (ESR) spectrum is suitable for that purpose, that is, detection of the spin nematic order under strong fields. We show that the longrange spin nematic order generates a characteristic resonance peak that clearly reflects the condensation of the bound magnon pair. 
Thursday, March 8, 2018 3:18PM  3:30PM 
V24.00003: Nematic Bond Theory of Frustrated Heisenberg Magnets Michael Schecter, Olav Syljuåsen, Jens Paaske We study frustrated Heisenberg models with generically incommensurate ground states. A general theory for the latticenematic “order by disorder” transition is developed based on the selfconsistent determination of the effective exchange coupling bonds. In our approach, fluctuations of the constraint field imposing conservation of the local magnetic moment drive nematicity at low temperatures. The critical temperature is found to be highly sensitive to the peak helimagnetic wave vector, and vanishes continuously when approaching rotation symmetric Lifshitz points. Transitions between symmetry distinct nematic orders may occur by tuning the exchange parameters, leading to lines of finite temperature bicritical points. 
Thursday, March 8, 2018 3:30PM  3:42PM 
V24.00004: Emergent spin1 Haldane gap and ferroelectricity in a frustrated spin1/2 ladder Rb_{2}Cu_{2}Mo_{3}O_{12} Hiroshi Ueda, Shigeki Onoda, Yasuhiro Yamaguchi, Tsuyoshi Kimura, Daichi Yoshizawa, Masayuki Hagiwara, Masato Hagihara, Minoru Soda, Takatsugu Masuda, Toshio Sakakibara, Keisuke Tomiyasu, Seiko Kawamura, Kenji Nakajima, Ryoichi Kajimoto, Mitsutaka Nakamura, Yasuhiro Inamura, Masashi Hase, Yukio Yasui Nontrivial ground states appear in frustrated spin1/2 chains involving ferromagnetic firstneighbor and antiferromagnetic secondneighbor exchange interactions, where spinsinglet shortrange resonating valence bonds connect emergent spin1 pairs with and without a spontaneously broken parity due to a vector spin chirality order. We report that the frustrated spin1/2 ladder material Rb_{2}Cu_{2}Mo_{3}O_{12}, on which a ferroelectricity stabilized by a magnetic field has been reported, hosts effective spin1 pairs forming a tetramer singlet ground state with the Haldane spin gap. Three lowestenergy spin excitations split from the spin1 triplet by DzyaloshinskiMoriya interactions are identified in inelastic neutronscattering and electron spin resonance spectra. Overall experimentally measured magnetic properties are explained from numerical simulations on a frustrated spin1/2 twoleg ladder model. 
Thursday, March 8, 2018 3:42PM  3:54PM 
V24.00005: Cooper Pair Induced Frustration and Nematicity of TwoDimensional Magnetic Adatom Lattices Jens Paaske, Michael Schecter, Olav Syljuåsen We propose utilizing the Cooper pair to induce magnetic frustration in systems of twodimensional (2D) magnetic adatom lattices on swave superconducting surfaces. The competition between singlet electron correlations and the RKKY coupling is shown to lead to a variety of hidden order states that break the pointgroup symmetry of the 2D adatom lattice at finite temperature. The phase diagram is constructed using a newly developed effective bond theory [M. Schecter et al., Phys. Rev. Lett. 119, 157202 (2017)], and exhibits broad regions of longrange vestigial nematic order. 
Thursday, March 8, 2018 3:54PM  4:06PM 
V24.00006: Dynamical structure factor of frustrated spin models: a variational Monte Carlo approach Federico Becca, Francesco Ferrari, Sandro Sorella The spin dynamical structure factor is computed within a variational framework to study frustrated Heisenberg models in one and two dimensions. Within this approach, the relevant part of the spectrum is approximated by considering twospinon excitations over the best variational Ansatz for the groundstate wave function. A benchmark of this approach on the onedimensional J_{1}J_{2} model give an excellent description of both the gapless and gapped (dimerized) phases, also describing the incommensurate structure for large frustrating ratios J_{2}/J_{1}. In the square lattice, we are able to unveil the dynamical signatures of the transition between the Neel and the (gapless) spinliquid phases that takes place for J_{2}/J_{1}=0.45. 
Thursday, March 8, 2018 4:06PM  4:18PM 
V24.00007: Structural distortion and magnetic dimerization in the new frustrated spin ladder Li_{2}O(CuSO_{4})_{2} Ornella Vaccarelli, Andreas Honecker, Andres Saul, Paola Giura, Björn Fåk, Gwenaelle Rousse, Guillaume Radtke Despite decades of theoretical work devoted to the study of frustrated spin ladders (see, e.g., [1] and references therein), real material realizations of such systems still remain limited. In this work, we investigate the magnetic properties of the new compound Li_{2}O(CuSO_{4})_{2} [2], which appears as a rare realization of a frustrated twoleg spin ladder in its hightemperature tetragonal structure [3]. Through a combined experimental and theoretical approach, we demonstrate that most of the magnetic frustration is removed by a structural transition, occurring at about 135K, and leading to a strong magnetic dimerization of the Cu ions [4]. Furthermore, we present recent results obtained from infrared spectroscopy and inelastic neutron scattering, providing first information on the magnetic excitations in this system. 
Thursday, March 8, 2018 4:18PM  4:54PM 
V24.00008: GMAG Student Dissertation Award: Amplitude mode in a spatially anisotropic 2D lattice: αNaMnO2 Invited Speaker: Rebecca Dally The orbitally active system, αNaMnO_{2}, has long been intriguing to researchers for its potential as a cathode material; however it is also known to possess intriguing magnetic properties. The lattice is fundamentally comprised of a triangular lattice of edgesharing MnO_{6} octahedra separated by sheets of Na cations. A cooperative JahnTeller distortion of the MnO_{6} octahedra (Mn^{3+}, t_{2g}^{3}e_{g}^{1}, S=2) restructures this hexagonal plane and directly affects the electronic (ferroorbital) and magnetic (antiferromagnetic) properties. The JahnTeller distortion results in the formation of an anisotropic triangular motif in the basal plane, where nearest neighbor Mn atoms, along the baxis, are much closer than nextnearest neighbor Mn atoms. The magnetic lattice thus behaves as weakly coupled spin chains with predominately 1D spin excitations. The magnon dispersion resulting from linear spin wave theory of a J_{1}J_{2} Heisenberg model with singleion anisotropy, D, fits well to the expected transverse modes in the inelastic channel. Additionally, careful polarized neutron scattering experiments were carried out to confirm the surprising presence of an additional mode in the spin excitation spectra, which was determined to be longitudinally polarized. This coherent and longlived excitation is an unusual mode for a nominally classical antiferromagnet and its origins will be discussed. 
Thursday, March 8, 2018 4:54PM  5:06PM 
V24.00009: Dynamics of selfconsistent wave function for fermionic Hubbard model Hidemaro Suwa, GiaWei Chern, Kipton Barros, Cristian Batista We have developed an efficient method for the dynamical simulation for the fermionic Hubbard model. An auxiliary vector field decoupling fermions is introduced at each site, and the selfconsistent condition between the auxiliary fields and the noninteracting fermions is imposed for representing a physical state. The advantage of this approach relative to the conventional meanfield analysis is that the selfconsistent wave function includes spatial fluctuations of the local order parameter and captures the critical phenomena of the thermodynamic phase transition. We have calculated the dynamical spin structure factor and demonstrated that it reproduces the exact result for a 4×4 lattice within a few percent error. We have studied the evolution of the magnon dispersion as a function of the interaction parameter for large systems, where the number of sites is of order 10^{3}. We will present results for the dynamical response in equilibrium, as well as quench dynamics after changing the interaction parameter. 
Thursday, March 8, 2018 5:06PM  5:18PM 
V24.00010: Universal logarithmic correction in the Renyi entropy for the spin$S$ Heisenberg quantum antiferromagnet on the square and triangular lattices: a modified spinwave theory study DagVidar Bauer, John Ove Fjaerestad Recently there has been much interest in a signature of broken continuous symmetry in the Renyi entropy, in the form of a universal term that diverges logarithmically with the subsystem size and is proportional to the number of Goldstone modes $n_G$ [1]. Here we use modified spinwave theory to study the Renyi entropy for the spin$S$ Heisenberg quantum antiferromagnet on the square and triangular lattices. By considering a onedimensional (line) subsystem of length $L$ that wraps around an $L \times L$ torus, the eigenvalues of the reduced density matrix can be found analytically. Focusing especially on the part of the Renyi entropy that is independent of the Renyi index, we find that it contains a universal term $(n_G/2)\log L$ (where $n_G=2,3$ for the square and triangular lattice model, respectively) as well as an ''area law'' contribution $\propto L$. We also discuss the dependence on the spin $S$. We compare our findings with previous related works [1,2]. 
Thursday, March 8, 2018 5:18PM  5:30PM 
V24.00011: Schwinger boson theory of quantum frustrated twodimensional antiferromagnets Leonardo dos Santos Lima The frustrated twodimensional Heisenberg models are very important models in condensed matter physics being studied a lot using numerical techniques such as quantum Monte Carlo method (QMC) and density matrix renormalization group (DMRG). Hence, we have studied the phase transition and spin transport in the S=1/2 twodimensional Heisenberg antiferromagnetic model in different types of lattices and with secondneighbor interactions using the Schwinger boson representation of spins operators, which is know to be an important analytical tool . We calculate the critical parameters and the spin conductivity and analyze the behavior of the AC spin conductivity on the critical line of separation of the different phases of this model. 
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