Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session A29: Spin Glasses and Disordered Magnetic Materials |
Hide Abstracts |
Sponsoring Units: GMAG Chair: Ben Ueland, National Institute of Standards and Technology, Center for Neutron Research Room: 333 |
Monday, March 16, 2009 8:00AM - 8:12AM |
A29.00001: Probing the relation between structural glasses and 3-spin spin glasses using one-dimensional models Derek Larson, Helmut G. Katzgraber, A.P. Young Motivated by a proposed connection between 3-spin spin glasses and structural glasses, we have performed Monte Carlo simulations on a one-dimensional long-range Ising glass with power-law interactions involving 3-spins. Varying the exponent of the power-law interactions is analogous to changing the space dimension of a corresponding short-range 3-spin model. We present results of a finite-size scaling analysis of the two-point correlation length, and compare our results with the prediction of Moore and Yeo that the three-spin model is in the same universality class as an Ising spin glass in a magnetic field. [Preview Abstract] |
Monday, March 16, 2009 8:12AM - 8:24AM |
A29.00002: Study of the de Almeida-Thouless line using power-law diluted one-dimensional Ising spin glasses Helmut G. Katzgraber, Derek A. Larson, A.P. Young We test the existence of a spin-glass state in an externally-applied (random) magnetic field via Monte Carlo simulations of a power-law diluted one-dimensional Ising spin glass. The model has the advantage over conventional short-range models in that by tuning the exponent of the power-law interactions we are able to scan the full range of possible behaviors from the infinite-range to the non-mean-field regime. Furthermore, due to the average fixed connectivity very large linear system sizes can be studied. An analysis of the two-point correlation length shows that the system in the non-mean-field universality class does not order in a field. This suggests that there is no de Almeida-Thouless line for short-range Ising spin glasses below the upper critical dimension. [Preview Abstract] |
Monday, March 16, 2009 8:24AM - 8:36AM |
A29.00003: Reentrant and Forward Phase Diagrams of the Anisotropic Three-Dimensional Ising Spin Glass Can G\"uven, A. Nihat Berker, Michael Hinczewski, Hidetoshi Nishimori The spatially uniaxially anisotropic d=3 Ising spin glass is solved exactly on a hierarchical lattice.[1] Five different ordered phases, namely ferromagnetic, columnar, layered, antiferromagnetic, and spin-glass phases, are found in the global phase diagram. The spin-glass phase is more extensive when randomness is introduced within the planes than when it is introduced in lines along one direction. Phase diagram cross-sections, with no Nishimori symmetry, with Nishimori symmetry lines, or entirely imbedded into Nishimori symmetry, are studied. The boundary between the ferromagnetic and spin-glass phases can be either reentrant or forward, that is either receding from or penetrating into the spin-glass phase, as temperature is lowered. However, this boundary is always reentrant when the multicritical point terminating it is on the Nishimori symmetry line. [1] C. G\"uven, A.N. Berker, M. Hinczewski, and H. Nishimori, Phys. Rev. E 77, 061110 (2008). [Preview Abstract] |
Monday, March 16, 2009 8:36AM - 8:48AM |
A29.00004: The Blume-Emery-Griffiths Spin Glass and Inverted Tricritical Points V. Ongun \"Oz\c{c}elik, A. Nihat Berker The Blume-Emery-Griffiths spin glass is studied by renormalization-group theory in d=3.[1] The boundary between the ferromagnetic and paramagnetic phases has first-order and two types of second-order segments. This topology includes an inverted tricritical point, first-order transitions replacing second-order transitions as temperature is lowered. The phase diagrams show disconnected spin-glass regions, spin-glass and paramagnetic reentrances, and complete reentrance, where the spin-glass phase replaces the ferromagnet as temperature is lowered for all chemical potentials. [1] V.O. \"Oz\c{c}elik and A.N. Berker, Phys. Rev. E 78, 031104 (2008). [Preview Abstract] |
Monday, March 16, 2009 8:48AM - 9:00AM |
A29.00005: Quenched-Vacancy Induced Spin-Glass Order G\"ul G\"ulpinar, A. Nihat Berker The ferromagnetic phase of an Ising model in d=3, with any amount of quenched antiferromagnetic bond randomness, is shown to undergo a transition to a spin-glass phase under sufficient quenched bond dilution.[1] This general result, demonstrated here with the numerically exact renormalization-group solution of a d=3 hierarchical lattice, is expected to hold true generally, for the cubic lattice and for quenched site dilution. Conversely, in the ferromagnetic-spinglass-antiferromagnetic phase diagram, the spin-glass phase expands under quenched dilution at the expense of the ferromagnetic and antiferromagnetic phases. In the ferro-spinglass phase transition induced by quenched dilution reentrance is seen, as previously found for the ferro-spinglass transition induced by increasing the antiferromagnetic bond concentration. [1] G. G\"ulpinar and A.N. Berker, arXiv:0811.0025v1 [cond- mat.dis-nn] (2008). [Preview Abstract] |
Monday, March 16, 2009 9:00AM - 9:12AM |
A29.00006: Nonequilibrium spin glass dynamics with the Janus computer David Yllanes, F. Belletti, A. Cruz, L.A. Fernandez, A. Gordillo-Guerrero, M. Guidetti, A. Maiorano, F. Mantovani, E. Marinari, V. Martin-Mayor, J. Monforte, A. Munoz Sudupe, D. Navarro, G. Parisi, S. Perez-Gaviro, J.J. Ruiz-Lorenzo, S.F. Schifano, D. Sciretti, A. Tarancon, R. Tripiccione The out of equilibrium evolution of the Edwards-Anderson spin glass is followed for a tenth of a second, effectively halving the (logarithmic) temporal gap between previous simulations and experiments. In fact, we have been able to make safe predictions about the behavior at experimental times, using mild extrapolations. This work has been made possible by Janus, a special purpose computer designed by our collaboration. We have thoroughly studied the spin glass correlation functions and the growth of the coherence length for $L\!=\!80$ lattices in $3D$,using $L\!=\!24,40$ lattices to check for finite size effects. We present clear evidence for a replicon correlator. Our main conclusion is that these spin glasses follow non-coarsening dynamics, at least up to the experimentally relevant time scales. [Preview Abstract] |
Monday, March 16, 2009 9:12AM - 9:24AM |
A29.00007: Chaotic Spin Correlations in Frustrated Ising Hierarchical Lattices Ne\c{s}e Aral, A. Nihat Berker Spin-spin correlations are calculated in frustrated hierarchical Ising models that exhibit chaotic renormalization-group behavior. [1] The spin-spin correlations, as a function of distance, behave chaotically. The far correlations, but not the near correlations, are sensitive to small changes in temperature or frustration, with temperature changes having a larger effect. On the other hand, the calculated free energy, internal energy, and entropy are smooth functions of temperature. The recursion-matrix calculation of thermodynamic densities in a chaotic band is demonstrated. The spectrum of Lyapunov exponents is calculated as a function of frustration. [1] N. Aral and A.N. Berker, arXiv:0810.4586v1 [cond-mat.dis-nn] (2008). [Preview Abstract] |
Monday, March 16, 2009 9:24AM - 9:36AM |
A29.00008: Tunable domain pinning in a Random-Field Ising Ferromagnet D. M. Silevitch, G. Aeppli, T.F. Rosenbaum The diluted magnetic salt $\mathrm{Li(Ho,Y)F}_4$ was shown recently [Nature {\bf 448} 567-570 (2007)] to be the first ferromagnetic realization of the random-field Ising model, where the strength of the random fields can be tuned by an external magnetic field. These random-field effects can be used to continuously and reversibly vary the pinning potential of the magnetic domains, allowing us to tune the hysteretic behavior. Magnetization measurements reveal enhanced pinning in the random-field regime as well as a temperature-dependent crossover into a regime dominated by quantum fluctuations. [Preview Abstract] |
Monday, March 16, 2009 9:36AM - 9:48AM |
A29.00009: A strongly disordered spin glass and minimum spanning trees Thomas Jackson, Nicholas Read We investigate the ground state structure of a strongly
disordered spin glass model proposed by Newman and Stein (NS). In
the strong disorder limit, frustration is negligible and the
problem of identifying ground states is equivalent to the minimum
spanning tree (MST) problem in combinatorial optimization: given
an edge-weighted graph, the MST is the subset of edges that
connects all vertices, has no cycles, and minimizes the total
edge weight. Here the weights are quenched random variables, and
we use a relation between Kruskal's greedy algorithm for finding
the MST and percolation. We solve this random MST on the Bethe
lattice with appropriate boundary conditions, which defines a
mean-field theory valid above $d_c=6$ (NS proposed $d_c=8$).
Above $d_c$, NS showed that the spin glass model has infinitely
many ground states, but only a single pair below $d_c$. For
$d |
Monday, March 16, 2009 9:48AM - 10:00AM |
A29.00010: ABSTRACT WITHDRAWN |
Monday, March 16, 2009 10:00AM - 10:12AM |
A29.00011: Overlap as a Measure of Spin-Glass Memory and a Probe of Free Energy Landscape Wen Luo, Michael Mihalco, Thomas E. Stone, Susan R. McKay The degree of history dependence and the structure of the free energy landscape of the spin glass are both indicators of the complexity of this ordered phase. Using the Ising antiferromagnet on a triangular lattice, diluted with quenched random ferromagnetic bonds, we probe these indicators through repeated cycling between two temperatures. We consider cases in which both temperatures are within the spin-glass phase, and systematically vary the temperature difference between initial and final states. These results are compared with the same cycling pattern with one temperature inside and the other outside of the spin-glass phase. The average overlap between low-temperature states provides a quantitative measure of the system's memory, and is non-zero when the system remains within the spin-glass phase during cycling. A plot of the overlaps of the low temperature states and their differences in internal energy shows no simple relationship between overlap and internal energy. States with almost identical internal energies often have very little overlap. [Preview Abstract] |
Monday, March 16, 2009 10:12AM - 10:24AM |
A29.00012: Quantum Effects for Interaction of Electron with coupled magnetic local spin chains Fatih Dogan, Lucian Covaci, Wonkee Kim, Frank Marsiglio In this talk, we will look at time dependent interaction of an electron with ferromagnetic chain. We will show that ferromagnetic interactions between magnetic spins cause the electron interacting with them to change its energy and depending on the strength of interactions form a bound state. These effects are visible through the resulting state of the electron. Experimental suggestions will be given to observe this quantum behavior. [Preview Abstract] |
Monday, March 16, 2009 10:24AM - 10:36AM |
A29.00013: Avalanche Spatial Structure: Viewing Crackling Noise through Windows Yan-Jiun Chen, Stefanos Papanikolaou, James P. Sethna, Gianfranco Durin, Stefano Zapperi In imaging experiments of Barkhausen noise in thin films, magnetic avalanches at the boundaries present challenges to analysis. Large avalanches are removed from the distribution, and the portion inside the viewing window may sometimes be treated as smaller avalanches. We analyze the scaling behavior of different categories of avalanches in artificially-windowed simulations of Barkhausen noise to examine the effect of window size on scaling relations. In passing, we discuss the average spatial shapes of avalanches, multivariable scaling functions, and the use of nonlinear-least-squares methods for exploring and reporting universal scaling functions. [Preview Abstract] |
Monday, March 16, 2009 10:36AM - 10:48AM |
A29.00014: Avalanche Average Shapes: Mean-field temporal average avalanche shape Stefanos Papanikolaou, Christopher R. Myers, Francesca Colaiori, Karen E. Daniels, Gianfranco Durin, Stefano Zapperi, James P. Sethna The average temporal shape of avalanches has been a fruitful application of universality and critical scaling, with experimental and theoretical investigations particularly in the field of magnetic Barkhausen noise. The mean-field shapes of these avalanches have been thought to come in two forms: inverted parabolas for the infinite-range model and one lobe of a sinusoid for the single-degree of freedom ABBM model. We show that the infinite-range model can be mapped onto the earlier ABBM model, and that the average shape for both mean field theories is an inverted parabola, seemingly resolving the ambiguity. However, we also propose a new mean-field model including the effects of local saddle-node bifurcations on the dynamics, and analyze both its predictions for dynamical exponents and temporal average shapes. We compare with experimental results on sheared granular materials. [Preview Abstract] |
Monday, March 16, 2009 10:48AM - 11:00AM |
A29.00015: Permutation Symmetric Critical Phases in Disordered Non-Abelian Anyonic Chains Lukasz Fidkowski, Gil Refael, Han-Hsuan Lin, Paraj Titum Topological phases supporting non-abelian anyonic excitations have been proposed as candidates for topological quantum computation. We study disordered non-abelian anyonic chains based on the quantum groups $SU(2)_k$, a hierarchy that includes the $\nu=5/2$ FQH state and the proposed $\nu=12/5$ Fibonacci state, among others. We find that for odd $k$ these anyonic chains realize infinite randomness critical {\it phases} in the same universality class as the $S_k$ permutation symmetric multi-critical points of Damle and Huse (arXiv:cond-mat/0207244). Indeed, we show that the pertinent subspace of these anyonic chains actually maps to the ${Z}_k \subset S_k$ symmetric sector of the Damle-Huse model, and this ${Z}_k$ symmetry stabilizes the phase. [Preview Abstract] |
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