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Sample records for kagome ising model

  1. High temperature series expansions for the susceptibility of Ising model on the Kagome lattice with nearest neighber interactions

    Directory of Open Access Journals (Sweden)

    Z Jalali mola

    2011-12-01

    Full Text Available  The Ising model is one of the simplest models describing the interacting particles. In this work, we calculate the high temperature series expansions of zero field susceptibility of ising model with ferromagnetic, antiferromagnetic and one antiferromagnetic interactions on two dimensional kagome lattice. Using the Pade´ approximation, we calculate the susceptibility of critical exponent of ferromagnetic ising model γ ≈ 1.75, which is consistent with universality hypothesis. However, antiferromagnetic and one antiferromagnetic interaction ising model doesn’t show any transition at finite temperature because of the effect of magnetic frustration.

  2. Thermodynamic geometry of a kagome Ising model in a magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Mirza, B., E-mail: b.mirza@cc.iut.ac.ir [Department of Physics, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of); Talaei, Z., E-mail: zs_talaie@ph.iut.ac.ir [Department of Physics, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of)

    2013-02-15

    We derived the thermodynamic curvature of the Ising model on a kagome lattice under the presence of an external magnetic field. The curvature was found to have a singularity at the critical point. We focused on the zero field case to derive thermodynamic curvature and its components near the criticality. According to standard scaling, scalar curvature R behaves as |β−β{sub c}|{sup α−2} for α>0 where β is the inverse temperature and α is the critical exponent of specific heat. In the model considered here in which α is zero, we found that R behaves as |β−β{sub c}|{sup α−1}.

  3. Emergent order in the kagome Ising magnet Dy3Mg2Sb3O14

    Science.gov (United States)

    Paddison, Joseph A. M.; Ong, Harapan S.; Hamp, James O.; Mukherjee, Paromita; Bai, Xiaojian; Tucker, Matthew G.; Butch, Nicholas P.; Castelnovo, Claudio; Mourigal, Martin; Dutton, S. E.

    2016-12-01

    The Ising model--in which degrees of freedom (spins) are binary valued (up/down)--is a cornerstone of statistical physics that shows rich behaviour when spins occupy a highly frustrated lattice such as kagome. Here we show that the layered Ising magnet Dy3Mg2Sb3O14 hosts an emergent order predicted theoretically for individual kagome layers of in-plane Ising spins. Neutron-scattering and bulk thermomagnetic measurements reveal a phase transition at ~0.3 K from a disordered spin-ice-like regime to an emergent charge ordered state, in which emergent magnetic charge degrees of freedom exhibit three-dimensional order while spins remain partially disordered. Monte Carlo simulations show that an interplay of inter-layer interactions, spin canting and chemical disorder stabilizes this state. Our results establish Dy3Mg2Sb3O14 as a tuneable system to study interacting emergent charges arising from kagome Ising frustration.

  4. Geometric frustration effects in the spin-1 antiferromagnetic Ising model on the kagome-like recursive lattice: exact results

    Science.gov (United States)

    Jurčišinová, E.; Jurčišin, M.

    2016-09-01

    The antiferromagnetic spin-1 Ising model is studied on the Husimi lattice constructed from elementary triangles with coordination number z  =  4. It is found that the model has a unique solution for arbitrary values of the magnetic field as well as for all temperatures. A detailed analysis of the magnetization is performed and it is shown that in addition to the standard plateau-like ground states, the model also contains well-defined single-point ground states related to definite values of the magnetic field. Exact values of the residual entropies for all ground states are found. The properties of the susceptibility and the specific heat of the model are also discussed. The existence of the Schottky-type behavior of the specific heat and the strong magnetocaloric effect for low enough temperatures and for the external magnetic field close to the values at which the single-point ground states exist are identified.

  5. Antiferromagnetic Ising model on the swedenborgite lattice

    NARCIS (Netherlands)

    Buhrandt, Stefan; Fritz, Lars

    2014-01-01

    Geometrical frustration in spin systems often results in a large number of degenerate ground states. In this work, we study the antiferromagnetic Ising model on the three-dimensional swedenborgite lattice, which is a specific stacking of kagome and triangular layers. The model contains two exchange

  6. Complex-temperature singularities of Ising models

    CERN Document Server

    Shrock, R E

    1995-01-01

    We report new results on complex-temperature properties of Ising models. These include studies of the s=1/2 model on triangular, honeycomb, kagom\\'e, 3 \\cdot 12^2, and 4 \\cdot 8^2 lattices. We elucidate the complex--T phase diagrams of the higher-spin 2D Ising models, using calculations of partition function zeros. Finally, we investigate the 2D Ising model in an external magnetic field, mapping the complex--T phase diagram and exploring various singularities therein. For the case \\beta H=i\\pi/2, we give exact results on the phase diagram and obtain susceptibility exponents \\gamma' at various singularities from low-temperature series analyses.

  7. Study of the Antiferromagnetic Blume-Capel Model on kagomé Lattice

    Science.gov (United States)

    Hwang, Chi-Ok; Park, Sojeong; Kwak, Wooseop

    2016-09-01

    We study the anti-ferromagnetic (AF) Ising model and the AF Blume-Capel (BC) model on the kagomé lattice. Using the Wang-Landau sampling method, we estimate the joint density functions for both models on the lattice, and we obtain the exact critical magnetic fields at zero temperature by using the micro-canonical analysis. We also show the patterns of critical lines for the models from micro-canonical analysis.

  8. Ising Model from Intertwiners

    CERN Document Server

    Dittrich, Bianca

    2013-01-01

    Spin networks appear in a number of areas, for instance in lattice gauge theories and in quantum gravity. They describe the contraction of intertwiners according to the underlying network. We show that a certain generating function of intertwiner contractions leads to the partition function of the 2d Ising model. This implies that the intertwiner model possesses a second order phase transition, thus leading to a continuum limit with propagating degrees of freedom.

  9. Learning planar ising models

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, Jason K [Los Alamos National Laboratory; Chertkov, Michael [Los Alamos National Laboratory; Netrapalli, Praneeth [STUDENT UT AUSTIN

    2010-11-12

    Inference and learning of graphical models are both well-studied problems in statistics and machine learning that have found many applications in science and engineering. However, exact inference is intractable in general graphical models, which suggests the problem of seeking the best approximation to a collection of random variables within some tractable family of graphical models. In this paper, we focus our attention on the class of planar Ising models, for which inference is tractable using techniques of statistical physics [Kac and Ward; Kasteleyn]. Based on these techniques and recent methods for planarity testing and planar embedding [Chrobak and Payne], we propose a simple greedy algorithm for learning the best planar Ising model to approximate an arbitrary collection of binary random variables (possibly from sample data). Given the set of all pairwise correlations among variables, we select a planar graph and optimal planar Ising model defined on this graph to best approximate that set of correlations. We present the results of numerical experiments evaluating the performance of our algorithm.

  10. Fermions as generalized Ising models

    Science.gov (United States)

    Wetterich, C.

    2017-04-01

    We establish a general map between Grassmann functionals for fermions and probability or weight distributions for Ising spins. The equivalence between the two formulations is based on identical transfer matrices and expectation values of products of observables. The map preserves locality properties and can be realized for arbitrary dimensions. We present a simple example where a quantum field theory for free massless Dirac fermions in two-dimensional Minkowski space is represented by an asymmetric Ising model on a euclidean square lattice.

  11. Fermions as generalized Ising models

    Directory of Open Access Journals (Sweden)

    C. Wetterich

    2017-04-01

    Full Text Available We establish a general map between Grassmann functionals for fermions and probability or weight distributions for Ising spins. The equivalence between the two formulations is based on identical transfer matrices and expectation values of products of observables. The map preserves locality properties and can be realized for arbitrary dimensions. We present a simple example where a quantum field theory for free massless Dirac fermions in two-dimensional Minkowski space is represented by an asymmetric Ising model on a euclidean square lattice.

  12. Unconventional fermi surface instabilities in the kagome Hubbard model.

    Science.gov (United States)

    Kiesel, Maximilian L; Platt, Christian; Thomale, Ronny

    2013-03-22

    We investigate the competing Fermi surface instabilities in the kagome tight-binding model. Specifically, we consider on-site and short-range Hubbard interactions in the vicinity of van Hove filling of the dispersive kagome bands where the fermiology promotes the joint effect of enlarged density of states and nesting. The sublattice interference mechanism devised by Kiesel and Thomale [Phys. Rev. B 86, 121105 (2012)] allows us to explain the intricate interplay between ferromagnetic fluctuations and other ordering tendencies. On the basis of the functional renormalization group used to obtain an adequate low-energy theory description, we discover finite angular momentum spin and charge density wave order, a twofold degenerate d-wave Pomeranchuk instability, and f-wave superconductivity away from van Hove filling. Together, this makes the kagome Hubbard model the prototypical scenario for several unconventional Fermi surface instabilities.

  13. Complex-temperature properties of the Ising model on 2D heteropolygonal lattices

    CERN Document Server

    Matveev, V; Matveev, Victor; Shrock, Robert

    1995-01-01

    Using exact results, we determine the complex-temperature phase diagrams of the 2D Ising model on three regular heteropolygonal lattices, (3 \\cdot 6 \\cdot 3 \\cdot 6) (kagom\\'{e}), (3 \\cdot 12^2), and (4 \\cdot 8^2) (bathroom tile), where the notation denotes the regular n-sided polygons adjacent to each vertex. We also work out the exact complex-temperature singularities of the spontaneous magnetisation. A comparison with the properties on the square, triangular, and hexagonal lattices is given. In particular, we find the first case where, even for isotropic spin-spin exchange couplings, the nontrivial non-analyticities of the free energy of the Ising model lie in a two-dimensional, rather than one-dimensional, algebraic variety in the z=e^{-2K} plane.

  14. Bose-Hubbard model on a kagome lattice with sextic ring-exchange terms

    Science.gov (United States)

    Rousseau, Valéry G.; Tam, Ka-Ming; Jarrell, Mark; Moreno, Juana

    2013-02-01

    High-order ring-exchange interactions are crucial for the study of quantum fluctuations on many highly frustrated systems. A versatile and efficient quantum Monte Carlo method, which can handle finite and essentially zero temperature and canonical and grand-canonical ensembles, has long been sought. In this paper, we present an exact quantum Monte Carlo study of a model of hard-core bosons with sixth-order ring-exchange interactions on a two-dimensional kagome lattice. By using the stochastic Green function algorithm with global space-time update, we show that the system becomes unstable in the limit of large ring-exchange interactions. It undergoes a phase separation at all fillings, except at (1)/(3) and (2)/(3) fillings for which the superfluid density vanishes and an unusual mixed valence bond and charge density ordered solid is formed. This explains the universal features seen in previous studies on various different models, such as the transverse-field Ising models, on a kagome lattice near the classical limit.

  15. A Solvable Decorated Ising Lattice Model

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    A decoratedlattice is suggested and the Ising model on it with three kinds of interactions K1, K2, and K3 is studied. Using an equivalent transformation, the square decorated Ising lattice is transformed into a regular square Ising lattice with nearest-neighbor, next-nearest-neighbor, and four-spin interactions, and the critical fixed point is found atK1 = 0.5769, K2 = -0.0671, and K3 = 0.3428, which determines the critical temperature of the system. It is also found that this system and the regular square Ising lattice, and the eight-vertex model belong to the same universality class.

  16. Topological transitions in Ising models

    CERN Document Server

    Jalal, Somenath; Lal, Siddhartha

    2016-01-01

    The thermal dynamics of the two-dimensional Ising model and quantum dynamics of the one-dimensional transverse-field Ising model (TFIM) are mapped to one another through the transfer-matrix formalism. We show that the fermionised TFIM undergoes a Fermi-surface topology-changing Lifshitz transition at its critical point. We identify the degree of freedom which tracks the Lifshitz transition via changes in topological quantum numbers (e.g., Chern number, Berry phase etc.). An emergent $SU(2)$ symmetry at criticality is observed to lead to a topological quantum number different from that which characterises the ordered phase. The topological transition is also understood via a spectral flow thought-experiment in a Thouless charge pump, revealing the bulk-boundary correspondence across the transition. The duality property of the phases and their entanglement content are studied, revealing a holographic relation with the entanglement at criticality. The effects of a non-zero longitudinal field and interactions tha...

  17. Ground-state phase diagram of the Kondo lattice model on triangular-to-kagome lattices

    OpenAIRE

    Akagi, Yutaka; Motome, Yukitoshi

    2012-01-01

    We investigate the ground-state phase diagram of the Kondo lattice model with classical localized spins on triangular-to-kagome lattices by using a variational calculation. We identify the parameter regions where a four-sublattice noncoplanar order is stable with a finite spin scalar chirality while changing the lattice structure from triangular to kagome continuously. Although the noncoplanar spin states appear in a wide range of parameters, the spin configurations on the kagome network beco...

  18. Critical properties of a dilute O(n) model on the kagome lattice

    NARCIS (Netherlands)

    Li, B.; Guo, W.; Blöte, H.W.J.

    2008-01-01

    A critical dilute O(n) model on the kagome lattice is investigated analytically and numerically. We employ a number of exact equivalences which, in a few steps, link the critical O(n) spin model on the kagome lattice to the exactly solvable critical q-state Potts model on the honeycomb lattice with

  19. Ising model for neural data

    DEFF Research Database (Denmark)

    Roudi, Yasser; Tyrcha, Joanna; Hertz, John

    2009-01-01

    extract the optimal couplings for subsets of size up to $200$ neurons, essentially exactly, using Boltzmann learning. We then study the quality of several approximate methods for finding the couplings by comparing their results with those found from Boltzmann learning. Two of these methods -- inversion......(dansk abstrakt findes ikke) We study pairwise Ising models for describing the statistics of multi-neuron spike trains, using data from a simulated cortical network. We explore efficient ways of finding the optimal couplings in these models and examine their statistical properties. To do this, we...... of the Thouless-Anderson-Palmer equations and an approximation proposed by Sessak and Monasson -- are remarkably accurate. Using these approximations for larger subsets of neurons, we find that extracting couplings using data from a subset smaller than the full network tends systematically to overestimate...

  20. Stable Degeneracies for Ising Models

    Science.gov (United States)

    Knauf, Andreas

    2016-10-01

    We introduce and consider the notion of stable degeneracies of translation invariant energy functions, taken at spin configurations of a finite Ising model. By this term we mean the lack of injectivity that cannot be lifted by changing the interaction. We show that besides the symmetry-induced degeneracies, related to spin flip, translation and reflection, there exist additional stable degeneracies, due to more subtle symmetries. One such symmetry is the one of the Singer group of a finite projective plane. Others are described by combinatorial relations akin to trace identities. Our results resemble traits of the length spectrum for closed geodesics on a Riemannian surface of constant negative curvature. There, stable degeneracy is defined w.r.t. Teichmüller space as parameter space.

  1. Ising model for distribution networks

    CERN Document Server

    Hooyberghs, H; Giuraniuc, C; Van Schaeybroeck, B; Indekeu, J O

    2012-01-01

    An elementary Ising spin model is proposed for demonstrating cascading failures (break-downs, blackouts, collapses, avalanches, ...) that can occur in realistic networks for distribution and delivery by suppliers to consumers. A ferromagnetic Hamiltonian with quenched random fields results from policies that maximize the gap between demand and delivery. Such policies can arise in a competitive market where firms artificially create new demand, or in a solidary environment where too high a demand cannot reasonably be met. Network failure in the context of a policy of solidarity is possible when an initially active state becomes metastable and decays to a stable inactive state. We explore the characteristics of the demand and delivery, as well as the topological properties, which make the distribution network susceptible of failure. An effective temperature is defined, which governs the strength of the activity fluctuations which can induce a collapse. Numerical results, obtained by Monte Carlo simulations of t...

  2. The spin-1/2 Kagome XXZ model in a field: competition between lattice nematic and solid orders

    CERN Document Server

    Kshetrimayum, Augustine; Orus, Roman; Poilblanc, Didier

    2016-01-01

    We study numerically the spin-1/2 XXZ model in a field on an infinite Kagome lattice. We use different algorithms based on infinite Projected Entangled Pair States (iPEPS) for this, namely: (i) an approach with simplex tensors and 9-site unit cell, and (ii) an approach based on coarse-graining three spins in the Kagome lattice and mapping it to a square-lattice model with local and nearest-neighbor interactions, with usual PEPS tensors, 6- and 12-site unit cells. We observe the emergence of a plateau in the magnetization at $m_z = \\frac{1}{3}$ as a function of the magnetic field, and focus on characterizing it as a function of the anisotropy, including the XY, Heisenberg, and Ising points. We find that the 9-site simplex-method produces degenerate -- within our accuracy -- (lattice) nematic and $\\sqrt{3} \\times \\sqrt{3}$ VBC-Solid states up to the Ising point. The 6- and 12-site coarse-grained PEPS methods also produce (almost) degenerate nematic and $\\sqrt{2} \\times \\sqrt{2}$ VBC-Solid order, although with a...

  3. The Ising model as a pedagogical tool

    Science.gov (United States)

    Smith, Ryan; Hart, Gus L. W.

    2010-10-01

    Though originally developed to analyze ferromagnetic systems, the Ising model also provides an excellent framework for modeling alloys. The original Ising model represented magnetic moments (up or down) by a +1 or -1 at each point on a lattice and allowed only nearest neighbors interactions to be non-zero. In alloy modeling, the values ±1 represent A and B atoms. The Ising Hamiltonian can be used in a Monte Carlo approach to simulate the thermodynamics of the system (e.g., an order-disorder transition occuring as the temperature is lowered). The simplicity of the model makes it an ideal starting point for a qualitative understanding of magnetism or configuration ordering in a metal. I will demonstrate the application of the Ising model in simple, two-dimensional ferromagnetic systems and alloys.

  4. Gapless chiral spin liquid in a kagome Heisenberg model

    Science.gov (United States)

    Bieri, Samuel; Messio, Laura; Bernu, Bernard; Lhuillier, Claire

    2015-08-01

    Motivated by recent experiments on the Heisenberg S =1 /2 quantum spin liquid candidate material kapellasite, we classify all possible chiral (time-reversal symmetry breaking) spin liquids with fermionic spinons on the kagome lattice. We obtain the phase diagram for the physically relevant extended Heisenberg model, comparing the energies of a wide range of microscopic variational wave functions. We propose that, at low temperature, kapellasite exhibits a gapless chiral spin liquid phase with spinon Fermi surfaces. This two-dimensional state inherits many properties of the nearby one-dimensional phase of decoupled antiferromagnetic spin chains, but also shows some remarkable differences. We discuss the spin structure factors and other physical properties.

  5. The anti-ferromagnetic Ising model on the simplest pure Husimi lattice: An exact solution

    Energy Technology Data Exchange (ETDEWEB)

    Jurčišinová, E., E-mail: jurcisine@saske.sk [Institute of Experimental Physics, SAS, Watsonova 47, 040 01 Košice (Slovakia); Jurčišin, M., E-mail: jurcisin@saske.sk [Institute of Experimental Physics, SAS, Watsonova 47, 040 01 Košice (Slovakia); Bobák, A., E-mail: andrej.bobak@upjs.sk [Department of Theoretical Physics and Astrophysics, Faculty of Science, P.J. Šafárik University, Park Angelinum 9, 040 01 Košice (Slovakia)

    2013-11-22

    The anti-ferromagnetic spin-1/2 Ising model on the pure Husimi lattice with three sites in the elementary polygon (p=3) and the coordination number z=4 is investigated. It represents the simplest approximation of the anti-ferromagnetic Ising model on the two-dimensional kagome lattice which takes into account effects of frustration. The exact analytical solution of the model is found and discussed. It is proven that the model does not exhibit the first order as well as the second order phase transitions. A detailed analysis of the magnetization properties is performed and the existence of the magnetization plateaus for low temperatures is shown. All possible ground states of the model are found and discussed.

  6. Ising Model on an Infinite Ladder Lattice

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    In this paper we propose an Ising model on an infinite ladder lattice, which is made of two infinite Ising spin chains with interactions. It is essentially a quasi-one-dimessional Ising model because the length of the ladder lattice is infinite, while its width is finite. We investigate the phase transition and dynamic behavior of Ising model on this quasi-one-dimessional system. We use the generalized transfer matrix method to investigate the phase transition of the system. It is found that there is no nonzero temperature phase transition in this system. At the same time, we are interested in Glauber dynamics. Based on that, we obtain the time evolution of the local spin magnetization by exactly solving a set of master equations.

  7. A spin-1 kagome antiferromagnet

    Science.gov (United States)

    Tovar, Mayra; Shtengel, Kirill; Refael, Gil

    2010-03-01

    We study a spin-1 antiferromagnet on the kagom'e lattice. We start by constructing a Klein-type SU(2) symmetric Hamiltonian which contains Heisenberg interactions between nearest and next-nearest neighbors as well as three-body terms. Our model Hamiltonian has an extensive degenerate ground state whose manifold is spanned by the AKLT-like valence bond states. We also perturb the parent Hamiltonian by introducing an enhancement to the nearest neighbor antiferromagnetic Heisenberg interactions. By projecting this perturbation onto the basis spanned by the unperturbed ground states, we derive an effective Hamiltonian which is dual to that of the transverse field antiferromagnetic Ising model on the triangular lattice. Based on the parameters of our model, we find it to be in the order-by-disorder phase. The ground state is a valence bond crystal stabilized by quantum fluctuations. We also discuss excitations, both magnetic and non-magnetic, and address their possible relevance to experiment.

  8. Chiral spin liquid in a frustrated anisotropic kagome Heisenberg model.

    Science.gov (United States)

    He, Yin-Chen; Sheng, D N; Chen, Yan

    2014-04-04

    Kalmeyer-Laughlin (KL) chiral spin liquid (CSL) is a type of quantum spin liquid without time-reversal symmetry, and it is considered as the parent state of an exotic type of superconductor--anyon superconductor. Such an exotic state has been sought for more than twenty years; however, it remains unclear whether it can exist in a realistic system where time-reversal symmetry is breaking (T breaking) spontaneously. By using the density matrix renormalization group, we show that KL CSL exists in a frustrated anisotropic kagome Heisenberg model, which has spontaneous T breaking. We find that our model has two topological degenerate ground states, which exhibit nonvanishing scalar chirality order and are protected by finite excitation gap. Furthermore, we identify this state as KL CSL by the characteristic edge conformal field theory from the entanglement spectrum and the quasiparticles braiding statistics extracted from the modular matrix. We also study how this CSL phase evolves as the system approaches the nearest-neighbor kagome Heisenberg model.

  9. Graphical representations of Ising and Potts models

    CERN Document Server

    Björnberg, Jakob E

    2010-01-01

    We study graphical representations for two related models. The first model is the transverse field quantum Ising model, an extension of the original Ising model which was introduced by Lieb, Schultz and Mattis in the 1960's. The second model is the space-time percolation process, which is closely related to the contact model for the spread of disease. We consider a `space-time' random-cluster model and explore a range of useful probabilistic techniques for studying it. The space-time Potts model emerges as a natural generalization of the quantum Ising model. The basic properties of the phase transitions in these models are treated, such as the fact that there is at most one unbounded FK-cluster, and the resulting lower bound on the critical value in $\\ZZ$. We also develop an alternative graphical representation of the quantum Ising model, called the random-parity representation. This representation is based on the random-current representation of the classical Ising model, and allows us to study in much great...

  10. Finite-temperature transition of the antiferromagnetic Heisenberg model on a distorted kagome lattice.

    Science.gov (United States)

    Masuda, Hiroshi; Okubo, Tsuyoshi; Kawamura, Hikaru

    2012-08-03

    Motivated by the recent experiment on kagome-lattice antiferromagnets, we study the zero-field ordering behavior of the antiferromagnetic classical Heisenberg model on a uniaxially distorted kagome lattice by Monte Carlo simulations. A first-order transition, which has no counterpart in the corresponding undistorted model, takes place at a very low temperature. The origin of the transition is ascribed to a cooperative proliferation of topological excitations inherent to the model.

  11. Models for guidance in kagome-structured hollow-core photonic crystal fibres.

    Science.gov (United States)

    Pearce, G J; Wiederhecker, G S; Poulton, C G; Burger, S; St J Russell, P

    2007-10-01

    We demonstrate by numerical simulation that the general features of the loss spectrum of photonic crystal fibres (PCF) with a kagome structure can be explained by simple models consisting of thin concentric hexagons or rings of glass in air. These easily analysed models provide increased understanding of the mechanism of guidance in kagome PCF, and suggest ways in which the high-loss resonances in the loss spectrum may be shifted.

  12. Multicritical behavior in dissipative Ising models

    CERN Document Server

    Overbeck, Vincent R; Gorshkov, Alexey V; Weimer, Hendrik

    2016-01-01

    We analyze theoretically the many-body dynamics of a dissipative Ising model in a transverse field using a variational approach. We find that the steady state phase diagram is substantially modified compared to its equilibrium counterpart, including the appearance of a multicritical point belonging to a different universality class. Building on our variational analysis, we establish a field-theoretical treatment corresponding to a dissipative variant of a Ginzburg-Landau theory, which allows us to compute the upper critical dimension of the system. Finally, we present a possible experimental realization of the dissipative Ising model using ultracold Rydberg gases.

  13. The Romance of the Ising Model

    CERN Document Server

    McCoy, Barry M

    2011-01-01

    The essence of romance is mystery. In this talk, given in honor of the 60th birthday of Michio Jimbo, I will explore the meaning of this for the Ising model beginning in 1946 with Bruria Kaufman and Willis Lamb, continuing with the wedding by Jimbo and Miwa in 1980 of the Ising model with the Painlev{\\'e} VI equation which had been first discovered by Picard in 1889. I will conclude with the current fascination of the magnetic susceptibility and explore some of the mysteries still outstanding.

  14. Quantum Ising model coupled with conducting electrons

    Energy Technology Data Exchange (ETDEWEB)

    Yamashita, Yasufumi; Yonemitsu, Kenji [Institute for Molecular Science, 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585 (Japan); Graduate University for Advanced studies, 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585 (Japan)

    2005-01-01

    The effect of photo-doping on the quantum paraelectric SrTiO{sub 3} is studied by using the one-dimensional quantum Ising model, where the Ising spin describes the effective lattice polarization of an optical phonon. Two types of electron-phonon couplings are introduced through the modulation of transfer integral via lattice deformations. After the exact diagonalization and the perturbation studies, we find that photo-induced low-density carriers can drastically alter quantum fluctuations when the system locates near the quantum critical point between the quantum para- and ferro-electric phases.

  15. Quantum Ising model coupled with conducting electrons

    Science.gov (United States)

    Yamashita, Yasufumi; Yonemitsu, Kenji

    2005-01-01

    The effect of photo-doping on the quantum paraelectric SrTiO3 is studied by using the one-dimensional quantum Ising model, where the Ising spin describes the effective lattice polarization of an optical phonon. Two types of electron-phonon couplings are introduced through the modulation of transfer integral via lattice deformations. After the exact diagonalization and the perturbation studies, we find that photo-induced low-density carriers can drastically alter quantum fluctuations when the system locates near the quantum critical point between the quantum para- and ferro-electric phases.

  16. Classical Ising Models Realised on Optical Lattices

    Science.gov (United States)

    Cirio, Mauro; Brennen, G. K.; Twamley, J.; Iblisdir, S.; Boada, O.

    2012-02-01

    We describe a simple quantum algorithm acting on a register of qubits in d spatial dimensions which computes statistical properties of d+1 dimensional classical Ising models. The algorithm works by measuring scattering matrix elements for quantum processes and Wick rotating to provide estimates for real partition functions of classical systems. This method can be implemented in a straightforward way in ensembles of qubits, e.g. three dimensional optical lattices with only nearest neighbor Ising like interactions. By measuring noise in the estimate useful information regarding location of critical points and scaling laws can be extracted for classical Ising models, possibly with inhomogeneity. Unlike the case of quantum simulation of quantum hamiltonians, this algorithm does not require Trotter expansion of the evolution operator and thus has the advantage of being amenable to fault tolerant gate design in a straightforward manner. Through this setting it is possible to study the quantum computational complexity of the estimation of a classical partition function for a 2D Ising model with non uniform couplings and magnetic fields. We provide examples for the 2 dimensional case.

  17. Bond diluted Ising model in 2D

    Directory of Open Access Journals (Sweden)

    Bouamrane Rachid

    2013-03-01

    Full Text Available The bond diluted Ising model is studied by Monte Carlo method. The simulation is carried out on a two dimensional square lattice with missing bonds and free boundary conditions. The aim of this work is to investigate the thermodynamical properties of this model for different disorder degree parameter σ. The critical temperature is determined from the Binder cumulant and is shown to decreases as the disorder parameter σ increases linearly.

  18. Ising Expansion for the Hubbard Model

    OpenAIRE

    Shi, Zhu-Pei; Singh, Rajiv R. P.

    1995-01-01

    We develop series expansions for the ground state properties of the Hubbard model, by introducing an Ising anisotropy into the Hamiltonian. For the two-dimensional (2D) square lattice half-filled Hubbard model, the ground state energy, local moment, sublattice magnetization, uniform magnetic susceptibility and spin stiffness are calculated as a function of $U/t$, where $U$ is the Coulomb constant and $t$ is the hopping parameter. Magnetic susceptibility data indicate a crossover around $U\\app...

  19. Antiferromagnetic Ising Model in Hierarchical Networks

    Science.gov (United States)

    Cheng, Xiang; Boettcher, Stefan

    2015-03-01

    The Ising antiferromagnet is a convenient model of glassy dynamics. It can introduce geometric frustrations and may give rise to a spin glass phase and glassy relaxation at low temperatures [ 1 ] . We apply the antiferromagnetic Ising model to 3 hierarchical networks which share features of both small world networks and regular lattices. Their recursive and fixed structures make them suitable for exact renormalization group analysis as well as numerical simulations. We first explore the dynamical behaviors using simulated annealing and discover an extremely slow relaxation at low temperatures. Then we employ the Wang-Landau algorithm to investigate the energy landscape and the corresponding equilibrium behaviors for different system sizes. Besides the Monte Carlo methods, renormalization group [ 2 ] is used to study the equilibrium properties in the thermodynamic limit and to compare with the results from simulated annealing and Wang-Landau sampling. Supported through NSF Grant DMR-1207431.

  20. Classical Ising model test for quantum circuits

    Science.gov (United States)

    Geraci, Joseph; Lidar, Daniel A.

    2010-07-01

    We exploit a recently constructed mapping between quantum circuits and graphs in order to prove that circuits corresponding to certain planar graphs can be efficiently simulated classically. The proof uses an expression for the Ising model partition function in terms of quadratically signed weight enumerators (QWGTs), which are polynomials that arise naturally in an expansion of quantum circuits in terms of rotations involving Pauli matrices. We combine this expression with a known efficient classical algorithm for the Ising partition function of any planar graph in the absence of an external magnetic field, and the Robertson-Seymour theorem from graph theory. We give as an example a set of quantum circuits with a small number of non-nearest-neighbor gates which admit an efficient classical simulation.

  1. Ordering in Two-Dimensional Ising Models with Competing Interactions

    OpenAIRE

    2004-01-01

    We study the 2D Ising model on a square lattice with additional non-equal diagonal next-nearest neighbor interactions. The cases of classical and quantum (transverse) models are considered. Possible phases and their locations in the space of three Ising couplings are analyzed. In particular, incommensurate phases occurring only at non-equal diagonal couplings, are predicted. We also analyze a spin-pseudospin model comprised of the quantum Ising model coupled to XY spin chains in a particular ...

  2. Three representations of the Ising model

    Science.gov (United States)

    Kruis, Joost; Maris, Gunter

    2016-01-01

    Statistical models that analyse (pairwise) relations between variables encompass assumptions about the underlying mechanism that generated the associations in the observed data. In the present paper we demonstrate that three Ising model representations exist that, although each proposes a distinct theoretical explanation for the observed associations, are mathematically equivalent. This equivalence allows the researcher to interpret the results of one model in three different ways. We illustrate the ramifications of this by discussing concepts that are conceived as problematic in their traditional explanation, yet when interpreted in the context of another explanation make immediate sense. PMID:27698356

  3. Identifying interacting pairs of sites in infinite range Ising models

    CERN Document Server

    Galves, Antonio; Takahashi, Daniel Yasumasa

    2010-01-01

    We consider Ising models (pairwise interaction Gibbs probability measures) in $\\Z^d$ with an infinite range potential. We address the problem of identifying pairs of interacting sites from a finite sample of independent realisations of the Ising model. The sample contains only the values assigned by the Ising model to a finite set of sites in $\\Z^d$. Our main result is an upperbound for the probability with our estimator to misidentify the pairs of interacting sites in this finite set.

  4. Linear spin-wave study of a quantum kagome ice

    Science.gov (United States)

    Owerre, S. A.; Burkov, A. A.; Melko, Roger G.

    2016-04-01

    We present a large-S study of a quantum spin ice Hamiltonian, introduced by Huang et al. [Phys. Rev. Lett. 112, 167203 (2014), 10.1103/PhysRevLett.112.167203], on the kagome lattice. This model involves a competition between the frustrating Ising term of classical kagome ice, a Zeeman magnetic field h , and a nearest-neighbor transverse spin-flip term SixSjx-SiySjy . Recent quantum Monte Carlo (QMC) simulations by Carrasquilla et al. [Nat. Commun. 6, 7421 (2015), 10.1038/ncomms8421], uncovered lobes of a disordered phase for large Ising interaction and h ≠0 —a putative quantum spin liquid phase. Here, we examine the nature of this model using large-S expansion. We show that the ground state properties generally have the same trends with those observed in QMC simulations. In particular, the large-S ground state phase diagram captures the existence of the disordered lobes.

  5. Nonequilibrium antiferromagnetic mixed-spin Ising model.

    Science.gov (United States)

    Godoy, Mauricio; Figueiredo, Wagner

    2002-09-01

    We studied an antiferromagnetic mixed-spin Ising model on the square lattice subject to two competing stochastic processes. The model system consists of two interpenetrating sublattices of spins sigma=1/2 and S=1, and we take only nearest neighbor interactions between pairs of spins. The system is in contact with a heat bath at temperature T, and the exchange of energy with the heat bath occurs via one-spin flip (Glauber dynamics). Besides, the system interacts with an external agency of energy, which supplies energy to it whenever two nearest neighboring spins are simultaneously flipped. By employing Monte Carlo simulations and a dynamical pair approximation, we found the phase diagram for the stationary states of the model in the plane temperature T versus the competition parameter between one- and two-spin flips p. We observed the appearance of three distinct phases, that are separated by continuous transition lines. We also determined the static critical exponents along these lines and we showed that this nonequilibrium model belongs to the universality class of the two-dimensional equilibrium Ising model.

  6. Another solution of 2D Ising model

    Science.gov (United States)

    Vergeles, S. N.

    2009-04-01

    The partition function of the Ising model on a two-dimensional regular lattice is calculated by using the matrix representation of a Clifford algebra (the Dirac algebra), with number of generators equal to the number of lattice sites. It is shown that the partition function over all loops in a 2D lattice including self-intersecting ones is the trace of a polynomial in terms of Dirac matrices. The polynomial is an element of the rotation group in the spinor representation. Thus, the partition function is a function of a character on an orthogonal group of a high degree in the spinor representation.

  7. Exact sampling hardness of Ising spin models

    Science.gov (United States)

    Fefferman, B.; Foss-Feig, M.; Gorshkov, A. V.

    2017-09-01

    We study the complexity of classically sampling from the output distribution of an Ising spin model, which can be implemented naturally in a variety of atomic, molecular, and optical systems. In particular, we construct a specific example of an Ising Hamiltonian that, after time evolution starting from a trivial initial state, produces a particular output configuration with probability very nearly proportional to the square of the permanent of a matrix with arbitrary integer entries. In a similar spirit to boson sampling, the ability to sample classically from the probability distribution induced by time evolution under this Hamiltonian would imply unlikely complexity theoretic consequences, suggesting that the dynamics of such a spin model cannot be efficiently simulated with a classical computer. Physical Ising spin systems capable of achieving problem-size instances (i.e., qubit numbers) large enough so that classical sampling of the output distribution is classically difficult in practice may be achievable in the near future. Unlike boson sampling, our current results only imply hardness of exact classical sampling, leaving open the important question of whether a much stronger approximate-sampling hardness result holds in this context. The latter is most likely necessary to enable a convincing experimental demonstration of quantum supremacy. As referenced in a recent paper [A. Bouland, L. Mancinska, and X. Zhang, in Proceedings of the 31st Conference on Computational Complexity (CCC 2016), Leibniz International Proceedings in Informatics (Schloss Dagstuhl-Leibniz-Zentrum für Informatik, Dagstuhl, 2016)], our result completes the sampling hardness classification of two-qubit commuting Hamiltonians.

  8. Highly Nonlinear Ising Model and Social Segregation

    CERN Document Server

    Sumour, M A; Shabat, M M

    2011-01-01

    The usual interaction energy of the random field Ising model in statistical physics is modified by complementing the random field by added to the energy of the usual Ising model a nonlinear term S^n were S is the sum of the neighbor spins, and n=0,1,3,5,7,9,11. Within the Schelling model of urban segregation, this modification corresponds to housing prices depending on the immediate neighborhood. Simulations at different temperatures, lattice size, magnetic field, number of neighbors and different time intervals showed that results for all n are similar, expect for n=3 in violation of the universality principle and the law of corresponding states. In order to find the critical temperatures, for large n we no longer start with all spins parallel but instead with a random configuration, in order to facilitate spin flips. However, in all cases we have a Curie temperature with phase separation or long-range segregation only below this Curie temperature, and it is approximated by a simple formula: Tc is proportion...

  9. ISE ISE

    Directory of Open Access Journals (Sweden)

    Virve-Anneli Vihman

    2010-01-01

    Full Text Available Käesolevas artiklis vaadeldakse nimetavas käändes pronoomeni ise kasutamist internetifoorumites, kus on märkimisväärselt palju näiteid ise kasutustest ilma lähtevormita, s.t ilma nimi- või asesõnata, millele ise viitab. Artikli põhiküsimuseks on, kas ise-t kasutataksegi süstemaatiliselt isikulise pronoomeni asemel lause subjektina. Täpsemalt uurime, (a kas ise käitub subjekti kohatäitjana (paikneb subjekti positsioonis, kui lauses muud subjekti pole; (b kas ta käitub topikuna nagu tüüpiline isikuline asesõna lause algul, ning kas ta sealjuures kaotab ise-le omast rõhutavat, tähelepanu suunavat omadust ning (c kas ise-t kasutatakse eelkõige 1. isikule viitamisel. Korpusanalüüsist selgub, et ilma lähtevormita ise-t on kasutatud rohkem kui pooltes lausetes ning eriti sageli seoses 1. isiku väljendamisega. Samuti allub ise V2-reeglist tingitud inversioonile. Samas ei ole ka verbi ees kasutatud ise täielikult kaotanud rõhutavat funktsiooni. Ise kasutamine personaalse pronoomeni asemel subjekti positsioonis on ilmselt seotud negatiivsest (distantseerivast viisakusstrateegiast tingitud impersonaliseerimisega: vajadus rõhutavat, vastandavat 1. isiku pronoomenit vältida võib olla tinginud ise sagedase kasutamise subjekti positsioonis.

  10. Charged Ising Model of Neutron Star Matter

    CERN Document Server

    Hasnaoui, K H O

    2012-01-01

    Background: The inner crust of a neutron star is believed to consist of Coulomb-frustrated complex structures known as "nuclear pasta" that display interesting and unique low-energy dynamics. Purpose: To elucidate the structure and composition of the neutron-star crust as a function of temperature, density, and proton fraction. Methods: A new lattice-gas model, the "Charged-Ising Model" (CIM), is introduced to simulate the behavior of neutron-star matter. Preliminary Monte Carlo simulations on 30^3 lattices are performed for a variety of temperatures, densities, and proton fractions. Results: Results are obtained for the heat capacity, pair-correlation function, and static structure factor for a variety of conditions appropriate to the inner stellar crust. Conclusions: Although relatively simple, the CIM captures the essence of Coulomb frustration that is required to simulate the subtle dynamics of the inner stellar crust. Moreover, the computationally demanding long-range Coulomb interactions have been pre-c...

  11. The Worm Process for the Ising Model is Rapidly Mixing

    Science.gov (United States)

    Collevecchio, Andrea; Garoni, Timothy M.; Hyndman, Timothy; Tokarev, Daniel

    2016-09-01

    We prove rapid mixing of the worm process for the zero-field ferromagnetic Ising model, on all finite connected graphs, and at all temperatures. As a corollary, we obtain a fully-polynomial randomized approximation scheme for the Ising susceptibility, and for a certain restriction of the two-point correlation function.

  12. Unveiling the physics of the doped phase of the t - J model on the kagome lattice.

    Science.gov (United States)

    Guertler, Siegfried; Monien, Hartmut

    2013-08-30

    We investigate the ground state properties of the kagome lattice t - J model at low doping by variational Monte Carlo calculations. The resulting state possesses an interesting balance of spin exchange and kinetic exchange through the building blocks of stars which are linked by triangles and their internal hexagons. While the spin exchange is taking place mainly on the stars, hopping is favored on the hexagons. There is a density modulation, resulting in the holes having an effective static contribution. From this observation, how holes lead to dimerization in this model and why a particular valence bond crystal pattern is formed can be understood. Furthermore, we argue the optimal doping for this state. We discuss our result in connection with static impurities, and show the likely relevance to the diluted kagome lattice Heisenberg model, describing actual compounds.

  13. Duality and conformal twisted boundaries in the Ising model

    CERN Document Server

    Grimm, U

    2002-01-01

    There has been recent interest in conformal twisted boundary conditions and their realisations in solvable lattice models. For the Ising and Potts quantum chains, these amount to boundary terms that are related to duality, which is a proper symmetry of the model at criticality. Thus, at criticality, the duality-twisted Ising model is translationally invariant, similar to the more familiar cases of periodic and antiperiodic boundary conditions. The complete finite-size spectrum of the Ising quantum chain with this peculiar boundary condition is obtained.

  14. An Ising model for metal-organic frameworks

    Science.gov (United States)

    Höft, Nicolas; Horbach, Jürgen; Martín-Mayor, Victor; Seoane, Beatriz

    2017-08-01

    We present a three-dimensional Ising model where lines of equal spins are frozen such that they form an ordered framework structure. The frame spins impose an external field on the rest of the spins (active spins). We demonstrate that this "porous Ising model" can be seen as a minimal model for condensation transitions of gas molecules in metal-organic frameworks. Using Monte Carlo simulation techniques, we compare the phase behavior of a porous Ising model with that of a particle-based model for the condensation of methane (CH4) in the isoreticular metal-organic framework IRMOF-16. For both models, we find a line of first-order phase transitions that end in a critical point. We show that the critical behavior in both cases belongs to the 3D Ising universality class, in contrast to other phase transitions in confinement such as capillary condensation.

  15. Application of the Interface Approach in Quantum Ising Models

    OpenAIRE

    Sen, Parongama

    1997-01-01

    We investigate phase transitions in the Ising model and the ANNNI model in transverse field using the interface approach. The exact result of the Ising chain in a transverse field is reproduced. We find that apart from the interfacial energy, there are two other response functions which show simple scaling behaviour. For the ANNNI model in a transverse field, the phase diagram can be fully studied in the region where a ferromagnetic to paramagnetic phase transition occurs. The other region ca...

  16. The Information Service Evaluation (ISE Model

    Directory of Open Access Journals (Sweden)

    Laura Schumann

    2014-06-01

    Full Text Available Information services are an inherent part of our everyday life. Especially since ubiquitous cities are being developed all over the world their number is increasing even faster. They aim at facilitating the production of information and the access to the needed information and are supposed to make life easier. Until today many different evaluation models (among others, TAM, TAM 2, TAM 3, UTAUT and MATH have been developed to measure the quality and acceptance of these services. Still, they only consider subareas of the whole concept that represents an information service. As a holistic and comprehensive approach, the ISE Model studies five dimensions that influence adoption, use, impact and diffusion of the information service: information service quality, information user, information acceptance, information environment and time. All these aspects have a great impact on the final grading and of the success (or failure of the service. Our model combines approaches, which study subjective impressions of users (e.g., the perceived service quality, and user-independent, more objective approaches (e.g., the degree of gamification of a system. Furthermore, we adopt results of network economics, especially the "Success breeds success"-principle.

  17. The Gravity Dual of the Ising Model

    CERN Document Server

    Castro, Alejandra; Hartman, Thomas; Maloney, Alexander; Volpato, Roberto

    2011-01-01

    We evaluate the partition function of three dimensional theories of gravity in the quantum regime, where the AdS radius is Planck scale and the central charge is of order one. The contribution from the AdS vacuum sector can - with certain assumptions - be computed and equals the vacuum character of a minimal model CFT. The torus partition function is given by a sum over geometries which is finite and computable. For generic values of Newton's constant G and the AdS radius L the result has no Hilbert space interpretation, but in certain cases it agrees with the partition function of a known CFT. For example, the partition function of pure Einstein gravity with G=3L equals that of the Ising model, providing evidence that these theories are dual. We also present somewhat weaker evidence that the 3-state and tricritical Potts models are dual to pure higher spin theories of gravity based on SL(3) and E_6, respectively.

  18. Magnetic properties in kagomé lattice with RKKY interaction: A Monte Carlo study

    Science.gov (United States)

    Masrour, R.; Jabar, A.; Benyoussef, A.; Hamedoun, M.

    2016-03-01

    The magnetic properties of the kagomé lattice have been studied with Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange interactions in a spin-7/2 Ising model using Monte Carlo simulations. The RKKY interaction between the two magnetic layers is considered for different distances. The magnetizations and magnetic susceptibilities of this lattice are given for different triquadratic interactions around each triangular face. The critical temperature is obtained for a fixed size. The magnetic hysteresis cycle of kagomé lattice with RKKY interactions is obtained for different temperatures and for different crystal field with a fixed size of nonmagnetic layer.

  19. 2D Ising Model with a Defect Line

    CERN Document Server

    Cabra, D C

    1994-01-01

    We study the two-dimensional Ising model with a defect line and evaluate multipoint energy correlation functions using non-perturbative field-theoretical methods. We also discuss the evaluation of the two spin correlator on the defect line.

  20. Fermionic coset realization of the critical Ising model

    CERN Document Server

    Cabra, D C; Rothe, K D

    1995-01-01

    We obtain an explicit realization of all the primary fields of the Ising model in terms of a conformal field theory of constrained fermions. The four-point correlators of the energy, order and disorder operators are explicitly calculated.

  1. Metastability in an open quantum Ising model

    Science.gov (United States)

    Rose, Dominic C.; Macieszczak, Katarzyna; Lesanovsky, Igor; Garrahan, Juan P.

    2016-11-01

    We apply a recently developed theory for metastability in open quantum systems to a one-dimensional dissipative quantum Ising model. Earlier results suggest this model features either a nonequilibrium phase transition or a smooth but sharp crossover, where the stationary state changes from paramagnetic to ferromagnetic, accompanied by strongly intermittent emission dynamics characteristic of first-order coexistence between dynamical phases. We show that for a range of parameters close to this transition or crossover point the dynamics of the finite system displays pronounced metastability, i.e., the system relaxes first to long-lived metastable states before eventual relaxation to the true stationary state. From the spectral properties of the quantum master operator we characterize the low-dimensional manifold of metastable states, which are shown to be probability mixtures of two, paramagnetic and ferromagnetic, metastable phases. We also show that for long times the dynamics can be approximated by a classical stochastic dynamics between the metastable phases that is directly related to the intermittent dynamics observed in quantum trajectories and thus the dynamical phases.

  2. Partition function of nearest neighbour Ising models: Some new insights

    Indian Academy of Sciences (India)

    G Nandhini; M V Sangaranarayanan

    2009-09-01

    The partition function for one-dimensional nearest neighbour Ising models is estimated by summing all the energy terms in the Hamiltonian for N sites. The algebraic expression for the partition function is then employed to deduce the eigenvalues of the basic 2 × 2 matrix and the corresponding Hermitian Toeplitz matrix is derived using the Discrete Fourier Transform. A new recurrence relation pertaining to the partition function for two-dimensional Ising models in zero magnetic field is also proposed.

  3. On Complexity of the Quantum Ising Model

    Science.gov (United States)

    Bravyi, Sergey; Hastings, Matthew

    2017-01-01

    We study complexity of several problems related to the Transverse field Ising Model (TIM). First, we consider the problem of estimating the ground state energy known as the Local Hamiltonian Problem (LHP). It is shown that the LHP for TIM on degree-3 graphs is equivalent modulo polynomial reductions to the LHP for general k-local `stoquastic' Hamiltonians with any constant {k ≥ 2}. This result implies that estimating the ground state energy of TIM on degree-3 graphs is a complete problem for the complexity class {StoqMA} —an extension of the classical class {MA}. As a corollary, we complete the complexity classification of 2-local Hamiltonians with a fixed set of interactions proposed recently by Cubitt and Montanaro. Secondly, we study quantum annealing algorithms for finding ground states of classical spin Hamiltonians associated with hard optimization problems. We prove that the quantum annealing with TIM Hamiltonians is equivalent modulo polynomial reductions to the quantum annealing with a certain subclass of k-local stoquastic Hamiltonians. This subclass includes all Hamiltonians representable as a sum of a k-local diagonal Hamiltonian and a 2-local stoquastic Hamiltonian.

  4. Spin-1/2 kagome XXZ model in a field: Competition between lattice nematic and solid orders

    Science.gov (United States)

    Kshetrimayum, Augustine; Picot, Thibaut; Orús, Román; Poilblanc, Didier

    2016-12-01

    We study numerically the spin-1/2 XXZ model in a field on an infinite kagome lattice. We use different algorithms based on infinite projected entangled pair states (iPEPSs) for this, namely, (i) an approach with simplex tensors and a 9-site unit cell, and (ii) an approach based on coarse-graining three spins in the kagome lattice and mapping it to a square-lattice model with local and nearest-neighbor interactions, with the usual PEPS tensors, 6- and 12-site unit cells. Similarly to our previous calculation at the SU(2)-symmetric point (Heisenberg Hamiltonian), for any anisotropy from the Ising limit to the XY limit, we also observe the emergence of magnetization plateaus as a function of the magnetic field, at mz=1/3 using 6-, 9-, and 12-site PEPS unit cells, and at mz=1/9 ,5/9 , and 7/9 using a 9-site PEPS unit cell, the latter setup being able to accommodate √{3 }×√{3 } solid order. We also find that, at mz=1/3 , (lattice) nematic and √{3 }×√{3 } VBC-order states are degenerate within the accuracy of the nine-site simplex method, for all anisotropy. The 6- and 12-site coarse-grained PEPS methods produce almost-degenerate nematic and 1 ×2 VBC-solid orders. We also find that, within our accuracy, the six-site coarse-grained PEPS method gives slightly lower energies, which can be explained by the larger amount of entanglement this approach can handle, even in cases where the PEPS unit cell is not commensurate with the expected ground-state unit cell. Furthermore, we do not observe chiral spin liquid behaviors at and close to the XY point, as has been recently proposed. Our results are the first tensor network investigations of the XXZ model in a field and reveal the subtle competition between nearby magnetic orders in numerical simulations of frustrated quantum antiferromagnets, as well as the delicate interplay between energy optimization and symmetry in tensor network numerical simulations.

  5. Magnetic Properties and Thermal Entanglement on a Triangulated Kagome Lattice

    CERN Document Server

    Ananikian, N S; Chakhmakhchyan, L A; Kocharian, A N

    2011-01-01

    The magnetic and entanglement thermal (equilibrium) properties in spin-1/2 Ising-Heisenberg model on a triangulated Kagome lattice are analyzed by means of variational mean-field like treatment based on Gibbs-Bogoliubov inequality. Because of the separable character of Ising-type exchange interactions between the Heisenberg trimers the calculation of quantum entanglement in a self-consistent field can be performed for each of the trimers individually. The concurrence in terms of three qubit isotropic Heisenberg model in effective Ising field is non-zero even in the absence of a magnetic field. The magnetic and entanglement properties exhibit common (plateau and peak) features observable via (antferromagnetic) coupling constant and external magnetic field. The critical temperature for the phase transition and threshold temperature for concurrence coincide in the case of antiferromagnetic coupling between qubits. The existence of entangled and disentangled phases in saturated and frustrated phases is establishe...

  6. Exact interface model for wetting in the planar Ising model

    Science.gov (United States)

    Upton, P. J.

    1999-10-01

    At the wetting transition in the two-dimensional Ising model the long contour (interface) gets depinned from the substrate. It is found that on sufficiently large length scales the statistics of the long contour are described by a unique probability measure corresponding to a continuous ``interface model'' with an interface binding ``potential'' given by a Dirac δ function supported on the substrate. A lattice solid-on-solid model is shown to give similar results.

  7. Exact interface model for wetting in the planar Ising model.

    Science.gov (United States)

    Upton, P J

    1999-10-01

    At the wetting transition in the two-dimensional Ising model the long contour (interface) gets depinned from the substrate. It is found that on sufficiently large length scales the statistics of the long contour are described by a unique probability measure corresponding to a continuous "interface model" with an interface binding "potential" given by a Dirac delta function supported on the substrate. A lattice solid-on-solid model is shown to give similar results.

  8. Critical parameters and universal amplitude ratios of two-dimensional spin-S Ising models using high- and low-temperature expansions

    CERN Document Server

    Butera, P

    2003-01-01

    For the study of Ising models of general spin S on the square lattice, we have combined our recently extended high-temperature expansions with the low-temperature expansions derived some time ago by Enting, Guttmann and Jensen. We have computed for the first time various critical parameters and improved the estimates of others. Moreover the properties of hyperscaling and of universality (spin S independence) of exponents and of various dimensionless amplitude combinations have been verified accurately. Assuming the validity of the lattice-lattice scaling, from our estimates of critical amplitudes for the square lattice we have also obtained estimates of the corresponding amplitudes for the spin S Ising model on the triangular, honeycomb, and kagome` lattices.

  9. Distinct spin liquids and their transitions in spin-1/2 XXZ kagome antiferromagnets.

    Science.gov (United States)

    He, Yin-Chen; Chen, Yan

    2015-01-23

    By using the density matrix renormalization group approach, we study spin-liquid phases of spin-1/2 XXZ kagome antiferromagnets. We find that the emergence of the spin-liquid phase is independent of the anisotropy of the XXZ interaction. In particular, the two extreme limits-the Ising (a strong S^{z} interaction) and the XY (zero S^{z} interaction)-host the same spin-liquid phases as the isotropic Heisenberg model. Both a time-reversal-invariant spin liquid and a chiral spin liquid with spontaneous time-reversal symmetry breaking are obtained. We show that they evolve continuously into each other by tuning the second- and the third-neighbor interactions. And last, we discuss possible implications of our results for the nature of spin liquid in nearest-neighbor XXZ kagome antiferromagnets, including the nearest-neighbor spin-1/2 kagome antiferromagnetic Heisenberg model.

  10. Order and thermalized dynamics in Heisenberg-like square and Kagomé spin ices.

    Science.gov (United States)

    Wysin, G M; Pereira, A R; Moura-Melo, W A; de Araujo, C I L

    2015-02-25

    Thermodynamic properties of a spin ice model on a Kagomé lattice are obtained from dynamic simulations and compared with properties in square lattice spin ice. The model assumes three-component Heisenberg-like dipoles of an array of planar magnetic islands situated on a Kagomé lattice. Ising variables are avoided. The island dipoles interact via long-range dipolar interactions and are restricted in their motion due to local shape anisotropies. We define various order parameters and obtain them and thermodynamic properties from the dynamics of the system via a Langevin equation, solved by the Heun algorithm. Generally, a slow cooling from high to low temperature does not lead to a particular state of order, even for a set of coupling parameters that gives well thermalized states and dynamics. At very low temperature, however, square ice is more likely to reach states near the ground state than Kagomé ice, for the same island coupling parameters.

  11. Layered kagome spin ice

    Science.gov (United States)

    Hamp, James; Dutton, Sian; Mourigal, Martin; Mukherjee, Paromita; Paddison, Joseph; Ong, Harapan; Castelnovo, Claudio

    Spin ice materials provide a rare instance of emergent gauge symmetry and fractionalisation in three dimensions: the effective degrees of freedom of the system are emergent magnetic monopoles, and the extensively many `ice rule' ground states are those devoid of monopole excitations. Two-dimensional (kagome) analogues of spin ice have also been shown to display a similarly rich behaviour. In kagome ice however the ground-state `ice rule' condition implies the presence everywhere of magnetic charges. As temperature is lowered, an Ising transition occurs to a charge-ordered state, which can be mapped to a dimer covering of the dual honeycomb lattice. A second transition, of Kosterlitz-Thouless or three-state Potts type, occurs to a spin-ordered state at yet lower temperatures, due to small residual energy differences between charge-ordered states. Inspired by recent experimental capabilities in growing spin ice samples with selective (layered) substitution of non-magnetic ions, in this work we investigate the fate of the two ordering transitions when individual kagome layers are brought together to form a three-dimensional pyrochlore structure coupled by long range dipolar interactions. We also consider the response to substitutional disorder and applied magnetic fields.

  12. Mathematical structure of three - dimensional (3D) Ising model

    CERN Document Server

    Zhang, Zhi-dong

    2013-01-01

    An overview of the mathematical structure of the three-dimensional (3D) Ising model is given, from the viewpoints of topologic, algebraic and geometric aspects. By analyzing the relations among transfer matrices of the 3D Ising model, Reidemeister moves in the knot theory, Yang-Baxter and tetrahedron equations, the following facts are illustrated for the 3D Ising model: 1) The complexified quaternion basis constructed for the 3D Ising model represents naturally the rotation in a (3 + 1) - dimensional space-time, as a relativistic quantum statistical mechanics model, which is consistent with the 4-fold integrand of the partition function by taking the time average. 2) A unitary transformation with a matrix being a spin representation in 2^(nlo)-space corresponds to a rotation in 2nlo-space, which serves to smooth all the crossings in the transfer matrices and contributes as the non-trivial topologic part of the partition function of the 3D Ising model. 3) A tetrahedron relation would ensure the commutativity o...

  13. Ising model for a Brownian donkey

    Science.gov (United States)

    Cleuren, B.; Van den Broeck, C.

    2001-04-01

    We introduce a thermal engine consisting of N interacting Brownian particles moving in a periodic potential, featuring an alternation of hot and cold symmetric peaks. A discretized Ising-like version is solved analytically. In response to an external force, absolute negative mobility is observed for N >= 4. For N → ∞ a nonequilibrium phase transition takes place with a spontaneous symmetry breaking entailing the appearance of a current in the absence of an external force.

  14. Fractional charge separation in the hard-core Bose Hubbard Model on the Kagome Lattice

    Science.gov (United States)

    Zhang, Xue Feng; Eggert, Sebastian

    2013-03-01

    We consider the hard core Bose Hubbard Model on a Kagome lattice with fixed (open) boundary conditions on two edges. We find that the fixed boundary conditions lift the degeneracy and freeze the system at 1/3 and 2/3 filling at small hopping. At larger hopping strengths, fractional charges spontaneously separate and are free to move to the edges of the system, which leads to a novel compressible phase with solid order. The compressibility is due to excitations on the edge which display a chrial symmetry breaking that is reminiscent of the quantum Hall effect. Large scale Monte Carlo simulations confirm the analytical calculations.

  15. Chiral spin liquid in the extended Heisenberg model on the Kagome lattice

    Science.gov (United States)

    Hu, Wenjun; Zhu, Wei; Zhang, Yi; Gong, Shoushu; Becca, Federico; Sheng, Dongning; Donna Sheng Team

    2015-03-01

    We investigate the extended Heisenberg model on the Kagome lattice by using Gutzwiller projected fermionic states and the variational Monte Carlo technique. In particular, when both second- and third-neighbor super-exchanges are considered, we find that a gapped spin liquid described by non-trivial magnetic fluxes and long-range chiral-chiral correlations is energetically favored compared to the gapless U(1) Dirac state. Furthermore, the topological Chern number, obtained by integrating the Berry curvature, and the degeneracy of the ground state, by constructing linearly independent states, lead us to identify this flux state as the chiral spin liquid with C = 1 / 2 fractionalized Chern number.

  16. Conformal invariance in the long-range Ising model

    Energy Technology Data Exchange (ETDEWEB)

    Paulos, Miguel F. [CERN, Theory Group, Geneva (Switzerland); Rychkov, Slava, E-mail: slava.rychkov@lpt.ens.fr [CERN, Theory Group, Geneva (Switzerland); Laboratoire de Physique Théorique de l' École Normale Supérieure (LPTENS), Paris (France); Faculté de Physique, Université Pierre et Marie Curie (UPMC), Paris (France); Rees, Balt C. van [CERN, Theory Group, Geneva (Switzerland); Zan, Bernardo [Institute of Physics, Universiteit van Amsterdam, Amsterdam (Netherlands)

    2016-01-15

    We consider the question of conformal invariance of the long-range Ising model at the critical point. The continuum description is given in terms of a nonlocal field theory, and the absence of a stress tensor invalidates all of the standard arguments for the enhancement of scale invariance to conformal invariance. We however show that several correlation functions, computed to second order in the epsilon expansion, are nontrivially consistent with conformal invariance. We proceed to give a proof of conformal invariance to all orders in the epsilon expansion, based on the description of the long-range Ising model as a defect theory in an auxiliary higher-dimensional space. A detailed review of conformal invariance in the d-dimensional short-range Ising model is also included and may be of independent interest.

  17. Conformal invariance in the long-range Ising model

    Directory of Open Access Journals (Sweden)

    Miguel F. Paulos

    2016-01-01

    Full Text Available We consider the question of conformal invariance of the long-range Ising model at the critical point. The continuum description is given in terms of a nonlocal field theory, and the absence of a stress tensor invalidates all of the standard arguments for the enhancement of scale invariance to conformal invariance. We however show that several correlation functions, computed to second order in the epsilon expansion, are nontrivially consistent with conformal invariance. We proceed to give a proof of conformal invariance to all orders in the epsilon expansion, based on the description of the long-range Ising model as a defect theory in an auxiliary higher-dimensional space. A detailed review of conformal invariance in the d-dimensional short-range Ising model is also included and may be of independent interest.

  18. Interacting damage models mapped onto ising and percolation models

    Energy Technology Data Exchange (ETDEWEB)

    Toussaint, Renaud; Pride, Steven R.

    2004-03-23

    The authors introduce a class of damage models on regular lattices with isotropic interactions between the broken cells of the lattice. Quasistatic fiber bundles are an example. The interactions are assumed to be weak, in the sense that the stress perturbation from a broken cell is much smaller than the mean stress in the system. The system starts intact with a surface-energy threshold required to break any cell sampled from an uncorrelated quenched-disorder distribution. The evolution of this heterogeneous system is ruled by Griffith's principle which states that a cell breaks when the release in potential (elastic) energy in the system exceeds the surface-energy barrier necessary to break the cell. By direct integration over all possible realizations of the quenched disorder, they obtain the probability distribution of each damage configuration at any level of the imposed external deformation. They demonstrate an isomorphism between the distributions so obtained and standard generalized Ising models, in which the coupling constants and effective temperature in the Ising model are functions of the nature of the quenched-disorder distribution and the extent of accumulated damage. In particular, they show that damage models with global load sharing are isomorphic to standard percolation theory, that damage models with local load sharing rule are isomorphic to the standard ising model, and draw consequences thereof for the universality class and behavior of the autocorrelation length of the breakdown transitions corresponding to these models. they also treat damage models having more general power-law interactions, and classify the breakdown process as a function of the power-law interaction exponent. Last, they also show that the probability distribution over configurations is a maximum of Shannon's entropy under some specific constraints related to the energetic balance of the fracture process, which firmly relates this type of quenched-disorder based

  19. An Ising model for earthquake dynamics

    Directory of Open Access Journals (Sweden)

    A. Jiménez

    2007-01-01

    Full Text Available This paper focuses on extracting the information contained in seismic space-time patterns and their dynamics. The Greek catalog recorded from 1901 to 1999 is analyzed. An Ising Cellular Automata representation technique is developed to reconstruct the history of these patterns. We find that there is strong correlation in the region, and that small earthquakes are very important to the stress transfers. Finally, it is demonstrated that this approach is useful for seismic hazard assessment and intermediate-range earthquake forecasting.

  20. Random field Ising model and community structure in complex networks

    Science.gov (United States)

    Son, S.-W.; Jeong, H.; Noh, J. D.

    2006-04-01

    We propose a method to determine the community structure of a complex network. In this method the ground state problem of a ferromagnetic random field Ising model is considered on the network with the magnetic field Bs = +∞, Bt = -∞, and Bi≠s,t=0 for a node pair s and t. The ground state problem is equivalent to the so-called maximum flow problem, which can be solved exactly numerically with the help of a combinatorial optimization algorithm. The community structure is then identified from the ground state Ising spin domains for all pairs of s and t. Our method provides a criterion for the existence of the community structure, and is applicable equally well to unweighted and weighted networks. We demonstrate the performance of the method by applying it to the Barabási-Albert network, Zachary karate club network, the scientific collaboration network, and the stock price correlation network. (Ising, Potts, etc.)

  1. Ising Model Coupled to Three-Dimensional Quantum Gravity

    CERN Document Server

    Baillie, C F

    1992-01-01

    We have performed Monte Carlo simulations of the Ising model coupled to three-dimensional quantum gravity based on a summation over dynamical triangulations. These were done both in the microcanonical ensemble, with the number of points in the triangulation and the number of Ising spins fixed, and in the grand canoncal ensemble. We have investigated the two possible cases of the spins living on the vertices of the triangulation (``diect'' case) and the spins living in the middle of the tetrahedra (``dual'' case). We observed phase transitions which are probably second order, and found that the dual implementation more effectively couples the spins to the quantum gravity.

  2. Large Scale Simulations of the Kinetic Ising Model

    Science.gov (United States)

    Münkel, Christian

    We present Monte Carlo simulation results for the dynamical critical exponent z of the two- and three-dimensional kinetic Ising model. The z-values were calculated from the magnetization relaxation from an ordered state into the equilibrium state at Tc for very large systems with up to (169984)2 and (3072)3 spins. To our knowledge, these are the largest Ising-systems simulated todate. We also report the successful simulation of very large lattices on a massively parallel MIMD computer with high speedups of approximately 1000 and an efficiency of about 0.93.

  3. A new efficient Cluster Algorithm for the Ising Model

    CERN Document Server

    Nyffeler, M; Wiese, U J; Nyfeler, Matthias; Pepe, Michele; Wiese, Uwe-Jens

    2005-01-01

    Using D-theory we construct a new efficient cluster algorithm for the Ising model. The construction is very different from the standard Swendsen-Wang algorithm and related to worm algorithms. With the new algorithm we have measured the correlation function with high precision over a surprisingly large number of orders of magnitude.

  4. Specific heat of the simple-cubic Ising model

    NARCIS (Netherlands)

    Feng, X.; Blöte, H.W.J.

    2010-01-01

    We provide an expression quantitatively describing the specific heat of the Ising model on the simple-cubic lattice in the critical region. This expression is based on finite-size scaling of numerical results obtained by means of a Monte Carlo method. It agrees satisfactorily with series expansions

  5. On scaling properties of cluster distributions in Ising models

    Science.gov (United States)

    Ruge, C.; Wagner, F.

    1992-01-01

    Scaling relations of cluster distributions for the Wolff algorithm are derived. We found them to be well satisfied for the Ising model in d=3 dimensions. Using scaling and a parametrization of the cluster distribution, we determine the critical exponent β/ν=0.516(6) with moderate effort in computing time.

  6. Topological Structures of Cluster Spins for Ising Models

    CERN Document Server

    Feng, You-gang

    2010-01-01

    We discussed hierarchies and rescaling rule of the self similar transformations in Ising models, and define a fractal dimension of an ordered cluster, which minimum corresponds to a fixed point of the transformations. By the fractal structures we divide the clusters into two types: irreducible and reducible. A relationship of cluster spin with its coordination number and fractal dimension is obtained.

  7. Ising Model Reprogramming of a Repeat Protein's Equilibrium Unfolding Pathway.

    Science.gov (United States)

    Millership, C; Phillips, J J; Main, E R G

    2016-05-08

    Repeat proteins are formed from units of 20-40 aa that stack together into quasi one-dimensional non-globular structures. This modular repetitive construction means that, unlike globular proteins, a repeat protein's equilibrium folding and thus thermodynamic stability can be analysed using linear Ising models. Typically, homozipper Ising models have been used. These treat the repeat protein as a series of identical interacting subunits (the repeated motifs) that couple together to form the folded protein. However, they cannot describe subunits of differing stabilities. Here we show that a more sophisticated heteropolymer Ising model can be constructed and fitted to two new helix deletion series of consensus tetratricopeptide repeat proteins (CTPRs). This analysis, showing an asymmetric spread of stability between helices within CTPR ensembles, coupled with the Ising model's predictive qualities was then used to guide reprogramming of the unfolding pathway of a variant CTPR protein. The designed behaviour was engineered by introducing destabilising mutations that increased the thermodynamic asymmetry within a CTPR ensemble. The asymmetry caused the terminal α-helix to thermodynamically uncouple from the rest of the protein and preferentially unfold. This produced a specific, highly populated stable intermediate with a putative dimerisation interface. As such it is the first step in designing repeat proteins with function regulated by a conformational switch. Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.

  8. Ising model on the generalized Bruhat-Tits tree

    Science.gov (United States)

    Zinoviev, Yu. M.

    1991-08-01

    The partition function and the correlation functions of the Ising model on the generalized Bruhat-Tits tree are calculated. We computed also the averages of these correlation functions when the corresponding vertices are attached to the boundary of the generalized Bruhat-Tits tree.

  9. Bond formation effects on the metal-insulator transition in the half-filled kagome Hubbard model

    Science.gov (United States)

    Higa, Ryota; Asano, Kenichi

    2016-06-01

    We study the metal-insulator transition in the half-filled Hubbard model on a Kagome lattice using the variational cluster approximation. The strong coupling limit of the model corresponds to the S =1 /2 Kagome Heisenberg antiferromagnet, which is known to have a singlet ground state, although its detail is still debated. As the results of the cluster methods generally depend much on the choice of the unit cluster, we have chosen the clusters that are compatible with these singlet ground states in the strong coupling case found so far, which basically consist of even number of sites. It is found that the correlated electrons on the Kagome lattice have a strong tendency to form valence-bond structures, which are the resonation of electrons on a single bond or several bonds forming loops. The zero-temperature metal-insulator transition at some interaction strength is possibly driven by the formation of such short range valence bonds and shows a second order character, which is distinctive from the Brinkman-Rice scenario. The electrons on these valence bonds further localizes onto each site as the interaction increases, and the valence bonds of electrons finally turn into magnetic singlet bonds between localized S =1 /2 spins, which are consistent with the ground states of the Kagome antiferromagnet.

  10. Ferroelectricity in a diatomic Ising chain as investigated by the elastic Ising model

    Institute of Scientific and Technical Information of China (English)

    Guo Yun-Jun; Wang Ke-Feng; Liu Jun-Ming

    2009-01-01

    An elastic Ising model for a one-dimensional diatomic spin chain is proposed to explain the ferroelectricity induced by the collinear magnetic order with a low-excited energy state. A statistical theory based on this model is developed to calculate the electrical and magnetic properties of Ca3CoMnO6, a typical quasi-one-dimensional diatomic spin chain system. The calculated ferroelectric polarization and dielectric susceptibility show a good agreement with recently reported data on Ca3Co2-xMnxO6 (x≈0.96) (Phys. Rev. Lett. 100 047601 (2008)), although the predicted magnetic susceptibility does not coincide well with experiment. We also address the rationality and deficiency of this model by including a first-order correction which improves the consistency between the model and experiment.

  11. Signatures of Dirac Cones in a DMRG Study of the Kagome Heisenberg Model

    Directory of Open Access Journals (Sweden)

    Yin-Chen He

    2017-07-01

    Full Text Available The antiferromagnetic spin-1/2 Heisenberg model on a kagome lattice is one of the most paradigmatic models in the context of spin liquids, yet the precise nature of its ground state is not understood. We use large-scale density matrix renormalization group simulations (DMRG on infinitely long cylinders and find indications for the formation of a gapless Dirac spin liquid. First, we use adiabatic flux insertion to demonstrate that the spin gap is much smaller than estimated from previous DMRG simulation. Second, we find that the momentum-dependent excitation spectrum, as extracted from the DMRG transfer matrix, exhibits Dirac cones that match those of a π-flux free-fermion model [the parton mean-field ansatz of a U(1 Dirac spin liquid].

  12. Exotic phase diagram of a cluster charging model of bosons on the kagome lattice

    Science.gov (United States)

    Isakov, Sergei V.; Paramekanti, Arun; Kim, Yong Baek

    2007-12-01

    We study a model of hard-core bosons on the kagome lattice with short-range hopping (t) and repulsive interactions (V) . This model directly maps onto an easy-axis S=1/2 XXZ model on the kagome lattice and is also related, at large V/t , to a quantum dimer model on the triangular lattice. Using quantum Monte Carlo numerics, we map out the phase diagram of this model at half-filling. At T=0 , we show that this model exhibits a superfluid phase at small V/t and an insulating phase at large V/t , separated by a continuous quantum phase transition at Vc/t≈19.8 . The insulating phase at T=0 appears to have no conventional broken symmetries, and is thus a uniform Mott insulator (a “spin liquid” in magnetic language). We characterize this insulating phase as a uniform Z2 fractionalized insulator from the topological order in the ground state and estimate its vison gap. Consistent with this identification, there is no apparent thermal phase transition upon heating the insulator. The insulating phase instead smoothly crosses over into the high temperature paramagnet via an intermediate cooperative paramagnetic regime. We also study the superfluid-to-normal thermal transition for V

  13. Chirality and Z2 vortices in a Heisenberg spin model on the kagome lattice

    Science.gov (United States)

    Domenge, J.-C.; Lhuillier, C.; Messio, L.; Pierre, L.; Viot, P.

    2008-05-01

    The phase diagram of the classical J1-J2 model on the kagome lattice is investigated by using extensive Monte Carlo simulations. In a realistic range of parameters, this model has a low-temperature chiral-ordered phase without long-range spin order. We show that the critical transition marking the destruction of the chiral order is preempted by the first-order proliferation of Z2 point defects. The core energy of these vortices appears to vanish when approaching the T=0 phase boundary, where both Z2 defects and gapless magnons contribute to disordering the system at very low temperatures. This situation might be typical of a large class of frustrated magnets. Possible relevance for real materials is also discussed.

  14. Minor magnetization loops in two-dimensional dipolar Ising model

    Energy Technology Data Exchange (ETDEWEB)

    Sarjala, M. [Aalto University, Department of Applied Physics, P.O. Box 14100, FI-00076 Aalto (Finland); Seppaelae, E.T., E-mail: eira.seppala@nokia.co [Nokia Research Center, Itaemerenkatu 11-13, FI-00180 Helsinki (Finland); Alava, M.J., E-mail: mikko.alava@tkk.f [Aalto University, Department of Applied Physics, P.O. Box 14100, FI-00076 Aalto (Finland)

    2011-05-15

    The two-dimensional dipolar Ising model is investigated for the relaxation and dynamics of minor magnetization loops. Monte Carlo simulations show that in a stripe phase an exponential decrease can be found for the magnetization maxima of the loops, M{approx}exp(-{alpha}N{sub l}) where N{sub l} is the number of loops. We discuss the limits of this behavior and its relation to the equilibrium phase diagram of the model.

  15. Kallen Lehman approach to 3D Ising model

    Science.gov (United States)

    Canfora, F.

    2007-03-01

    A “Kallen-Lehman” approach to Ising model, inspired by quantum field theory à la Regge, is proposed. The analogy with the Kallen-Lehman representation leads to a formula for the free-energy of the 3D model with few free parameters which could be matched with the numerical data. The possible application of this scheme to the spin glass case is shortly discussed.

  16. Critical dynamics of cluster algorithms in the dilute Ising model

    Science.gov (United States)

    Hennecke, M.; Heyken, U.

    1993-08-01

    Autocorrelation times for thermodynamic quantities at T C are calculated from Monte Carlo simulations of the site-diluted simple cubic Ising model, using the Swendsen-Wang and Wolff cluster algorithms. Our results show that for these algorithms the autocorrelation times decrease when reducing the concentration of magnetic sites from 100% down to 40%. This is of crucial importance when estimating static properties of the model, since the variances of these estimators increase with autocorrelation time. The dynamical critical exponents are calculated for both algorithms, observing pronounced finite-size effects in the energy autocorrelation data for the algorithm of Wolff. We conclude that, when applied to the dilute Ising model, cluster algorithms become even more effective than local algorithms, for which increasing autocorrelation times are expected.

  17. A MATLAB GUI to study Ising model phase transition

    Science.gov (United States)

    Thornton, Curtislee; Datta, Trinanjan

    We have created a MATLAB based graphical user interface (GUI) that simulates the single spin flip Metropolis Monte Carlo algorithm. The GUI has the capability to study temperature and external magnetic field dependence of magnetization, susceptibility, and equilibration behavior of the nearest-neighbor square lattice Ising model. Since the Ising model is a canonical system to study phase transition, the GUI can be used both for teaching and research purposes. The presence of a Monte Carlo code in a GUI format allows easy visualization of the simulation in real time and provides an attractive way to teach the concept of thermal phase transition and critical phenomena. We will also discuss the GUI implementation to study phase transition in a classical spin ice model on the pyrochlore lattice.

  18. Microcanonical Phase Diagram of the BEG and Ising Models

    Institute of Scientific and Technical Information of China (English)

    李粮生; 郑宁; 史庆藩

    2012-01-01

    The density of states of long-range Blume-Emery-Criffiths (BEG) and short-range lsing models are obtained by using Wang-Landau sampling with adaptive windows in energy and magnetization space. With accurate density of states, we are able to calculate the mierocanonical specific heat of fixed magnetization introduced by Kastner et al. in the regions of positive and negative temperature. The microcanonical phase diagram of the Ising model shows a continuous phase transition at a negative temperature in energy and magnetization plane. However the phase diagram of the long-range model constructed by peaks of the microeanonieal specific heat looks obviously different from the Ising chart.

  19. The Ising model in physics and statistical genetics.

    Science.gov (United States)

    Majewski, J; Li, H; Ott, J

    2001-10-01

    Interdisciplinary communication is becoming a crucial component of the present scientific environment. Theoretical models developed in diverse disciplines often may be successfully employed in solving seemingly unrelated problems that can be reduced to similar mathematical formulation. The Ising model has been proposed in statistical physics as a simplified model for analysis of magnetic interactions and structures of ferromagnetic substances. Here, we present an application of the one-dimensional, linear Ising model to affected-sib-pair (ASP) analysis in genetics. By analyzing simulated genetics data, we show that the simplified Ising model with only nearest-neighbor interactions between genetic markers has statistical properties comparable to much more complex algorithms from genetics analysis, such as those implemented in the Allegro and Mapmaker-Sibs programs. We also adapt the model to include epistatic interactions and to demonstrate its usefulness in detecting modifier loci with weak individual genetic contributions. A reanalysis of data on type 1 diabetes detects several susceptibility loci not previously found by other methods of analysis.

  20. Ising anyons in frustration-free Majorana-dimer models

    Science.gov (United States)

    Ware, Brayden; Son, Jun Ho; Cheng, Meng; Mishmash, Ryan V.; Alicea, Jason; Bauer, Bela

    2016-09-01

    Dimer models have long been a fruitful playground for understanding topological physics. Here, we introduce a class, termed Majorana-dimer models, wherein bosonic dimers are decorated with pairs of Majorana modes. We find that the simplest examples of such systems realize an intriguing, intrinsically fermionic phase of matter that can be viewed as the product of a chiral Ising theory, which hosts deconfined non-Abelian quasiparticles, and a topological px-i py superconductor. While the bulk anyons are described by a single copy of the Ising theory, the edge remains fully gapped. Consequently, this phase can arise in exactly solvable, frustration-free models. We describe two parent Hamiltonians: one generalizes the well-known dimer model on the triangular lattice, while the other is most naturally understood as a model of decorated fluctuating loops on a honeycomb lattice. Using modular transformations, we show that the ground-state manifold of the latter model unambiguously exhibits all properties of the Ising×(px-i py) theory. We also discuss generalizations with more than one Majorana mode per site, which realize phases related to Kitaev's 16-fold way in a similar fashion.

  1. Precision Islands in the Ising and $O(N)$ Models

    CERN Document Server

    Kos, Filip; Simmons-Duffin, David; Vichi, Alessandro

    2016-01-01

    We make precise determinations of the leading scaling dimensions and operator product expansion (OPE) coefficients in the 3d Ising, $O(2)$, and $O(3)$ models from the conformal bootstrap with mixed correlators. We improve on previous studies by scanning over possible relative values of the leading OPE coefficients, which incorporates the physical information that there is only a single operator at a given scaling dimension. The scaling dimensions and OPE coefficients obtained for the 3d Ising model, $(\\Delta_{\\sigma}, \\Delta_{\\epsilon},\\lambda_{\\sigma\\sigma\\epsilon}, \\lambda_{\\epsilon\\epsilon\\epsilon}) = (0.5181489(10), 1.412625(10), 1.0518537(41), 1.532435(19))$, give the most precise determinations of these quantities to date.

  2. Precision islands in the Ising and O(N) models

    Energy Technology Data Exchange (ETDEWEB)

    Kos, Filip [Department of Physics, Yale University, New Haven, CT 06520 (United States); Poland, David [Department of Physics, Yale University, New Haven, CT 06520 (United States); School of Natural Sciences, Institute for Advanced Study, Princeton, New Jersey 08540 (United States); Simmons-Duffin, David [School of Natural Sciences, Institute for Advanced Study, Princeton, New Jersey 08540 (United States); Vichi, Alessandro [Theory Division, CERN, Geneva (Switzerland)

    2016-08-04

    We make precise determinations of the leading scaling dimensions and operator product expansion (OPE) coefficients in the 3d Ising, O(2), and O(3) models from the conformal bootstrap with mixed correlators. We improve on previous studies by scanning over possible relative values of the leading OPE coefficients, which incorporates the physical information that there is only a single operator at a given scaling dimension. The scaling dimensions and OPE coefficients obtained for the 3d Ising model, (Δ{sub σ},Δ{sub ϵ},λ{sub σσϵ},λ{sub ϵϵϵ})=(0.5181489(10),1.412625(10),1.0518537(41),1.532435(19)), give the most precise determinations of these quantities to date.

  3. Quantum dimensions from local operator excitations in the Ising model

    CERN Document Server

    Caputa, Pawel

    2016-01-01

    We compare the time evolution of entanglement measures after local operator excitation in the critical Ising model with predictions from conformal field theory. For the spin operator and its descendants we find that Renyi entropies of a block of spins increase by a constant that matches the logarithm of the quantum dimension of the conformal family. However, for the energy operator we find a small constant contribution that differs from the conformal field theory answer equal to zero. We argue that the mismatch is caused by the subtleties in the identification between the local operators in conformal field theory and their lattice counterpart. Our results indicate that evolution of entanglement measures in locally excited states not only constraints this identification, but also can be used to extract non-trivial data about the conformal field theory that governs the critical point. We generalize our analysis to the Ising model away from the critical point, states with multiple local excitations, as well as t...

  4. Complete wetting in the three-dimensional transverse Ising model

    OpenAIRE

    Harris, A B; Micheletti, C.; Yeomans, J. M.

    1996-01-01

    We consider a three-dimensional Ising model in a transverse magnetic field, $h$ and a bulk field $H$. An interface is introduced by an appropriate choice of boundary conditions. At the point $(H=0,h=0)$ spin configurations corresponding to different positions of the interface are degenerate. By studying the phase diagram near this multiphase point using quantum-mechanical perturbation theory we show that that quantum fluctuations, controlled by $h$, split the multiphase degeneracy giving rise...

  5. Coupled modified baker's transformations for the Ising model.

    Science.gov (United States)

    Sakaguchi, H

    1999-12-01

    An invertible coupled map lattice is proposed for the Ising model. Each elemental map is a modified baker's transformation, which is a two-dimensional map of X and Y. The time evolution of the spin variable is memorized in the binary representation of the Y variable. The temporal entropy and time correlation of the spin variable are calculated from the snapshot configuration of the Y variables.

  6. One-dimensional Ising model with multispin interactions

    CERN Document Server

    Turban, L

    2016-01-01

    We study the spin-$1/2$ Ising chain with multispin interactions $K$ involving the product of $m$ successive spins, for general values of $m$. Using a change of spin variables the zero-field partition function of a finite chain is obtained for free and periodic boundary conditions (BC) and we calculate the two-spin correlation function. When placed in an external field $H$ the system is shown to be self-dual. Using another change of spin variables the one-dimensional (1D) Ising model with multispin interactions in a field is mapped onto a zero-field rectangular Ising model with first-neighbour interactions $K$ and $H$. The 2D system, with size $m\\times N/m$, has the topology of a cylinder with helical BC. In the thermodynamic limit $N/m\\to\\infty$, $m\\to\\infty$, a 2D critical singularity develops on the self-duality line, $\\sinh 2K\\sinh 2H=1$.

  7. Critical frontier of the Potts and percolation models on triangular-type and kagome-type lattices. II. Numerical analysis.

    Science.gov (United States)

    Ding, Chengxiang; Fu, Zhe; Guo, Wenan; Wu, F Y

    2010-06-01

    In the preceding paper, one of us (F. Y. Wu) considered the Potts model and bond and site percolation on two general classes of two-dimensional lattices, the triangular-type and kagome-type lattices, and obtained closed-form expressions for the critical frontier with applications to various lattice models. For the triangular-type lattices Wu's result is exact, and for the kagome-type lattices Wu's expression is under a homogeneity assumption. The purpose of the present paper is twofold: First, an essential step in Wu's analysis is the derivation of lattice-dependent constants A,B,C for various lattice models, a process which can be tedious. We present here a derivation of these constants for subnet networks using a computer algorithm. Second, by means of a finite-size scaling analysis based on numerical transfer matrix calculations, we deduce critical properties and critical thresholds of various models and assess the accuracy of the homogeneity assumption. Specifically, we analyze the q -state Potts model and the bond percolation on the 3-12 and kagome-type subnet lattices (n×n):(n×n) , n≤4 , for which the exact solution is not known. Our numerical determination of critical properties such as conformal anomaly and magnetic correlation length verifies that the universality principle holds. To calibrate the accuracy of the finite-size procedure, we apply the same numerical analysis to models for which the exact critical frontiers are known. The comparison of numerical and exact results shows that our numerical values are correct within errors of our finite-size analysis, which correspond to 7 or 8 significant digits. This in turn infers that the homogeneity assumption determines critical frontiers with an accuracy of 5 decimal places or higher. Finally, we also obtained the exact percolation thresholds for site percolation on kagome-type subnet lattices (1×1):(n×n) for 1≤n≤6 .

  8. Thermal Entanglement and Critical Behavior of Magnetic Properties on a Triangulated Kagomé Lattice

    Directory of Open Access Journals (Sweden)

    N. Ananikian

    2011-01-01

    Full Text Available The equilibrium magnetic and entanglement properties in a spin-1/2 Ising-Heisenberg model on a triangulated Kagomé lattice are analyzed by means of the effective field for the Gibbs-Bogoliubov inequality. The calculation is reduced to decoupled individual (clusters trimers due to the separable character of the Ising-type exchange interactions between the Heisenberg trimers. The concurrence in terms of the three qubit isotropic Heisenberg model in the effective Ising field in the absence of a magnetic field is non-zero. The magnetic and entanglement properties exhibit common (plateau, peak features driven by a magnetic field and (antiferromagnetic exchange interaction. The (quantum entangled and non-entangled phases can be exploited as a useful tool for signalling the quantum phase transitions and crossovers at finite temperatures. The critical temperature of order-disorder coincides with the threshold temperature of thermal entanglement.

  9. Corner wetting transition in the two-dimensional Ising model

    Science.gov (United States)

    Lipowski, Adam

    1998-07-01

    We study the interfacial behavior of the two-dimensional Ising model at the corner of weakened bonds. Monte Carlo simulations results show that the interface is pinned to the corner at a lower temperature than a certain temperature Tcw at which it undergoes a corner wetting transition. The temperature Tcw is substantially lower than the temperature of the ordinary wetting transition with a line of weakened bonds. A solid-on-solid-like model is proposed, which provides a supplementary description of the corner wetting transition.

  10. Ising model of financial markets with many assets

    Science.gov (United States)

    Eckrot, A.; Jurczyk, J.; Morgenstern, I.

    2016-11-01

    Many models of financial markets exist, but most of them simulate single asset markets. We study a multi asset Ising model of a financial market. Each agent has two possible actions (buy/sell) for every asset. The agents dynamically adjust their coupling coefficients according to past market returns and external news. This leads to fat tails and volatility clustering independent of the number of assets. We find that a separation of news into different channels leads to sector structures in the cross correlations, similar to those found in real markets.

  11. The hobbyhorse of magnetic systems: the Ising model

    Science.gov (United States)

    Ibarra-García-Padilla, Eduardo; Gerardo Malanche-Flores, Carlos; Poveda-Cuevas, Freddy Jackson

    2016-11-01

    In undergraduate statistical mechanics courses the Ising model always plays an important role because it is the simplest non-trivial model used to describe magnetic systems. The one-dimensional model is easily solved analytically, while the two-dimensional one can be solved exactly by the Onsager solution. For this reason, numerical simulations are usually used to solve the two-dimensional model. Keeping in mind that the two-dimensional model is the platform for studying phase transitions, it is usually an exercise in computational undergraduate courses because its numerical solution is relatively simple to implement and its critical exponents are perfectly known. The purpose of this article is to present a detailed numerical study of the second-order phase transition in the two-dimensional Ising model at an undergraduate level, allowing readers not only to compare the mean-field solution, the exact solution and the numerical one through a complete study of the order parameter, the correlation function and finite-size scaling, but to present the techniques, along with hints and tips, for solving it themselves. We present the elementary theory of phase transitions and explain how to implement Markov chain Monte Carlo simulations and perform them for different lattice sizes with periodic boundary conditions. Energy, magnetization, specific heat, magnetic susceptibility and the correlation function are calculated and the critical exponents determined by finite-size scaling techniques. The importance of the correlation length as the relevant parameter in phase transitions is emphasized.

  12. Defects in the tri-critical Ising model

    Science.gov (United States)

    Makabe, Isao; Watts, Gérard M. T.

    2017-09-01

    We consider two different conformal field theories with central charge c = 7 /10. One is the diagonal invariant minimal model in which all fields have integer spins; the other is the local fermionic theory with superconformal symmetry in which fields can have half-integer spin. We construct new conformal (but not topological or factorised) defects in the minimal model. We do this by first constructing defects in the fermionic model as boundary conditions in a fermionic theory of central charge c = 7 /5, using the folding trick as first proposed by Gang and Yamaguchi [1]. We then act on these with interface defects to find the new conformal defects. As part of the construction, we find the topological defects in the fermionic theory and the interfaces between the fermionic theory and the minimal model. We also consider the simpler case of defects in the theory of a single free fermion and interface defects between the Ising model and a single fermion as a prelude to calculations in the tri-critical Ising model.

  13. Complete wetting in the three-dimensional transverse Ising model

    Science.gov (United States)

    Harris, A. B.; Micheletti, C.; Yeomans, J. M.

    1996-08-01

    We consider a three-dimensional Ising model in a transverse magnetic field h and a bulk field H. An interface is introduced by an appropriate choice of boundary conditions. At the point ( H=0, h=0) spin configurations corresponding to different positions of the interface are degenerate. By studying the phase diagram near this multiphase point using quantum mechanical perturbation theory, we show that the quantum fluctuations, controlled by h, split the multiphase degeneracy giving rise to an infinite sequence of layering transitions.

  14. Fluctuation dissipation ratio in the one dimensional kinetic Ising model

    OpenAIRE

    Lippiello, E.; Zannetti, M.

    2000-01-01

    The exact relation between the response function $R(t,t^{\\prime})$ and the two time correlation function $C(t,t^{\\prime})$ is derived analytically in the one dimensional kinetic Ising model subjected to a temperature quench. The fluctuation dissipation ratio $X(t,t^{\\prime})$ is found to depend on time through $C(t,t^{\\prime})$ in the time region where scaling $C(t,t^{\\prime}) = f(t/t^{\\prime})$ holds. The crossover from the nontrivial form $X(C(t,t^{\\prime}))$ to $X(t,t^{\\prime}) \\equiv 1$ t...

  15. Ising model simulation in directed lattices and networks

    Science.gov (United States)

    Lima, F. W. S.; Stauffer, D.

    2006-01-01

    On directed lattices, with half as many neighbours as in the usual undirected lattices, the Ising model does not seem to show a spontaneous magnetisation, at least for lower dimensions. Instead, the decay time for flipping of the magnetisation follows an Arrhenius law on the square and simple cubic lattice. On directed Barabási-Albert networks with two and seven neighbours selected by each added site, Metropolis and Glauber algorithms give similar results, while for Wolff cluster flipping the magnetisation decays exponentially with time.

  16. Simulation of financial market via nonlinear Ising model

    Science.gov (United States)

    Ko, Bonggyun; Song, Jae Wook; Chang, Woojin

    2016-09-01

    In this research, we propose a practical method for simulating the financial return series whose distribution has a specific heaviness. We employ the Ising model for generating financial return series to be analogous to those of the real series. The similarity between real financial return series and simulated one is statistically verified based on their stylized facts including the power law behavior of tail distribution. We also suggest the scheme for setting the parameters in order to simulate the financial return series with specific tail behavior. The simulation method introduced in this paper is expected to be applied to the other financial products whose price return distribution is fat-tailed.

  17. Creep motion in a random-field Ising model.

    Science.gov (United States)

    Roters, L; Lübeck, S; Usadel, K D

    2001-02-01

    We analyze numerically a moving interface in the random-field Ising model which is driven by a magnetic field. Without thermal fluctuations the system displays a depinning phase transition, i.e., the interface is pinned below a certain critical value of the driving field. For finite temperatures the interface moves even for driving fields below the critical value. In this so-called creep regime the dependence of the interface velocity on the temperature is expected to obey an Arrhenius law. We investigate the details of this Arrhenius behavior in two and three dimensions and compare our results with predictions obtained from renormalization group approaches.

  18. Critical Exponents of Ferromagnetic Ising Model on Fractal Lattices

    Science.gov (United States)

    Hsiao, Pai-Yi

    2001-04-01

    We review the value of the critical exponents ν-1, β/ν, and γ/ν of ferromagnetic Ising model on fractal lattices of Hausdorff dimension between one and three. They are obtained by Monte Carlo simulation with the help of Wolff algorithm. The results are accurate enough to show that the hyperscaling law df = 2β/ν + γ/ν is satisfied in non-integer dimension. Nevertheless, the discrepancy between the simulation results and the γ-expansion studies suggests that the strong universality should be adapted for the fractal lattices.

  19. Modified Mean Field approximation for the Ising Model

    CERN Document Server

    Di Bartolo, Cayetano

    2009-01-01

    We study a modified mean-field approximation for the Ising Model in arbitrary dimension. Instead of taking a "central" spin, or a small "drop" of fluctuating spins coupled to the effective field of their nearest neighbors as in the Mean-Field or the Bethe-Peierls-Weiss methods, we take an infinite chain of fluctuating spins coupled to the mean field of the rest of the lattice. This results in a significative improvement of the Mean-Field approximation with a small extra effort.

  20. Surface critical behavior of the smoothly inhomogeneous Ising model

    Science.gov (United States)

    Burkhardt, Theodore W.; Guim, Ihnsouk

    1984-01-01

    We consider a semi-infinite two-dimensional Ising model with nearest-neighbor coupling constants that deviate from the bulk coupling by Am-y for large m, m being the distance from the edge. The case ALeeuwen. We report exact results for the boundary magnetization and boundary pair-correlation function when A>0. At the bulk critical temperature there is a rich variety of critical behavior in the A -y plane with both paramagnetic and ferromagnetic surface phases. Some of our results can be derived and generalized with simple scaling arguments.

  1. Kagome spin ice

    Science.gov (United States)

    Mellado, Paula

    Spin ice in magnetic pyrochlore oxides is a peculiar magnetic state. Like ordinary water ice, these materials are in apparent violation with the third law of thermodynamics, which dictates that the entropy of a system in thermal equilibrium vanishes as its temperature approaches absolute zero. In ice, a "zero-point" entropy is retained down to low temperatures thanks to a high number of low-energy positions of hydrogen ions associated with the Bernal-Fowler ice-rules. Spins in pyrochlore oxides Ho2Ti 2O7 and Dy2Ti2O7 exhibit a similar degeneracy of ground states and thus also have a sizable zero-point entropy. A recent discovery of excitations carrying magnetic charges in pyrochlore spin ice adds another interesting dimension to these magnets. This thesis is devoted to a theoretical study of a two-dimensional version of spin ice whose spins reside on kagome, a lattice of corner-sharing triangles. It covers two aspects of this frustrated classical spin system: the dynamics of artificial spin ice in a network of magnetic nanowires and the thermodynamics of crystalline spin ice. Magnetization dynamics in artificial spin ice is mediated by the emission, propagation and absorption of domain walls in magnetic nanowires. The dynamics shows signs of self-organized behavior such as avalanches. The theoretical model compares favorably to recent experiments. The thermodynamics of the microscopic version of spin ice on kagome is examined through analytical calculations and numerical simulations. The results show that, in addition to the high-temperature paramagnetic phase and the low-temperature phase with magnetic order, spin ice on kagome may have an intermediate phase with fluctuating spins and ordered magnetic charges. This work is concluded with a calculation of the entropy of kagome spin ice at zero temperature when one of the sublattices is pinned by an applied magnetic field and the system breaks up into independent spin chains, a case of dimensional reduction.

  2. Globally nilpotent differential operators and the square Ising model

    Energy Technology Data Exchange (ETDEWEB)

    Bostan, A [INRIA Rocquencourt, Domaine de Voluceau, BP 105 78153 Le Chesnay Cedex (France); Boukraa, S [LPTHIRM and Departement d' Aeronautique, Universite de Blida (Algeria); Hassani, S; Zenine, N [Centre de Recherche Nucleaire d' Alger, 2 Bd. Frantz Fanon, BP 399, 16000 Alger (Algeria); Maillard, J-M [LPTMC, CNRS, Universite de Paris, Tour 24, 4eme etage, Case 121, 4 Place Jussieu, 75252 Paris Cedex 05 (France); Weil, J-A [LACO, XLIM, Universite de Limoges, 123 Avenue Albert Thomas, 87060 Limoges Cedex (France)], E-mail: alin.bostan@inria.fr, E-mail: boukraa@mail.univ-blida.dz, E-mail: maillard@lptmc.jussieu.fr, E-mail: jacques-arthur.weil@unilim.fr, E-mail: njzenine@yahoo.com

    2009-03-27

    We recall various multiple integrals with one parameter, related to the isotropic square Ising model, and corresponding, respectively, to the n-particle contributions of the magnetic susceptibility, to the (lattice) form factors, to the two-point correlation functions and to their {lambda}-extensions. The univariate analytic functions defined by these integrals are holonomic and even G-functions: they satisfy Fuchsian linear differential equations with polynomial coefficients and have some arithmetic properties. We recall the explicit forms, found in previous work, of these Fuchsian equations, as well as their Russian-doll and direct sum structures. These differential operators are selected Fuchsian linear differential operators, and their remarkable properties have a deep geometrical origin: they are all globally nilpotent, or, sometimes, even have zero p-curvature. We also display miscellaneous examples of globally nilpotent operators emerging from enumerative combinatorics problems for which no integral representation is yet known. Focusing on the factorized parts of all these operators, we find out that the global nilpotence of the factors (resp. p-curvature nullity) corresponds to a set of selected structures of algebraic geometry: elliptic curves, modular curves, curves of genus five, six,..., and even a remarkable weight-1 modular form emerging in the three-particle contribution {chi}{sup (3)} of the magnetic susceptibility of the square Ising model. Noticeably, this associated weight-1 modular form is also seen in the factors of the differential operator for another n-fold integral of the Ising class, {phi}{sup (3)}{sub H}, for the staircase polygons counting, and in Apery's study of {zeta}(3). G-functions naturally occur as solutions of globally nilpotent operators. In the case where we do not have G-functions, but Hamburger functions (one irregular singularity at 0 or {infinity}) that correspond to the confluence of singularities in the scaling limit

  3. Oscillating hysteresis in the q-neighbor Ising model.

    Science.gov (United States)

    Jȩdrzejewski, Arkadiusz; Chmiel, Anna; Sznajd-Weron, Katarzyna

    2015-11-01

    We modify the kinetic Ising model with Metropolis dynamics, allowing each spin to interact only with q spins randomly chosen from the whole system, which corresponds to the topology of a complete graph. We show that the model with q≥3 exhibits a phase transition between ferromagnetic and paramagnetic phases at temperature T*, which linearly increases with q. Moreover, we show that for q=3 the phase transition is continuous and that it is discontinuous for larger values of q. For q>3, the hysteresis exhibits oscillatory behavior-expanding for even values of q and shrinking for odd values of q. Due to the mean-field-like nature of the model, we are able to derive the analytical form of transition probabilities and, therefore, calculate not only the probability density function of the order parameter but also precisely determine the hysteresis and the effective potential showing stable, unstable, and metastable steady states. Our results show that a seemingly small modification of the kinetic Ising model leads not only to the switch from a continuous to a discontinuous phase transition, but also to an unexpected oscillating behavior of the hysteresis and a puzzling phenomenon for q=5, which might be taken as evidence for the so-called mixed-order phase transition.

  4. Generic phase coexistence in the totally asymmetric kinetic Ising model

    Science.gov (United States)

    Godrèche, Claude; Luck, Jean-Marc

    2017-07-01

    The physical analysis of generic phase coexistence in the North-East-Center Toom model was originally given by Bennett and Grinstein. The gist of their argument relies on the dynamics of interfaces and droplets. We revisit the same question for a specific totally asymmetric kinetic Ising model on the square lattice. This nonequilibrium model possesses the remarkable property that its stationary-state measure in the absence of a magnetic field coincides with that of the usual ferromagnetic Ising model. We use both analytical arguments and numerical simulations in order to make progress in the quantitative understanding of the phenomenon of generic phase coexistence. At zero temperature a mapping onto the TASEP allows an exact determination of the time-dependent shape of the ballistic interface sweeping a large square minority droplet of up or down spins. At finite temperature, measuring the mean lifetime of such a droplet allows an accurate measurement of its shrinking velocity v, which depends on temperature T and magnetic field h. In the absence of a magnetic field, v vanishes with an exponent Δ_v≈2.5+/-0.2 as the critical temperature T c is approached. At fixed temperature in the ordered phase, v vanishes at the phase-boundary fields +/- h_b(T) which mark the limits of the coexistence region. The latter fields vanish with an exponent Δ_h≈3.2+/-0.3 as T c is approached.

  5. Ising percolation in a three-state majority vote model

    Energy Technology Data Exchange (ETDEWEB)

    Balankin, Alexander S., E-mail: abalankin@ipn.mx [Grupo Mecánica Fractal, ESIME, Instituto Politécnico Nacional, México D.F., 07738 (Mexico); Martínez-Cruz, M.A.; Gayosso Martínez, Felipe [Grupo Mecánica Fractal, ESIME, Instituto Politécnico Nacional, México D.F., 07738 (Mexico); Mena, Baltasar [Laboratorio de Ingeniería y Procesos Costeros, Instituto de Ingeniería, Universidad Nacional Autónoma de México, Sisal, Yucatán, 97355 (Mexico); Tobon, Atalo; Patiño-Ortiz, Julián; Patiño-Ortiz, Miguel; Samayoa, Didier [Grupo Mecánica Fractal, ESIME, Instituto Politécnico Nacional, México D.F., 07738 (Mexico)

    2017-02-05

    Highlights: • Three-state non-consensus majority voter model is introduced. • Phase transition in the absorbing state non-consensus is revealed. • The percolation transition belongs to the universality class of Ising percolation. • The effect of an updating rule for a tie between voter neighbors is highlighted. - Abstract: In this Letter, we introduce a three-state majority vote model in which each voter adopts a state of a majority of its active neighbors, if exist, but the voter becomes uncommitted if its active neighbors are in a tie, or all neighbors are the uncommitted. Numerical simulations were performed on square lattices of different linear size with periodic boundary conditions. Starting from a random distribution of active voters, the model leads to a stable non-consensus state in which three opinions coexist. We found that the “magnetization” of the non-consensus state and the concentration of uncommitted voters in it are governed by an initial composition of system and are independent of the lattice size. Furthermore, we found that a configuration of the stable non-consensus state undergoes a second order percolation transition at a critical concentration of voters holding the same opinion. Numerical simulations suggest that this transition belongs to the same universality class as the Ising percolation. These findings highlight the effect of an updating rule for a tie between voter neighbors on the critical behavior of models obeying the majority vote rule whenever a strict majority exists.

  6. Emergent chiral spin liquid: fractional quantum Hall effect in a kagome Heisenberg model.

    Science.gov (United States)

    Gong, Shou-Shu; Zhu, Wei; Sheng, D N

    2014-09-10

    The fractional quantum Hall effect (FQHE) realized in two-dimensional electron systems under a magnetic field is one of the most remarkable discoveries in condensed matter physics. Interestingly, it has been proposed that FQHE can also emerge in time-reversal invariant spin systems, known as the chiral spin liquid (CSL) characterized by the topological order and the emerging of the fractionalized quasiparticles. A CSL can naturally lead to the exotic superconductivity originating from the condense of anyonic quasiparticles. Although CSL was highly sought after for more than twenty years, it had never been found in a spin isotropic Heisenberg model or related materials. By developing a density-matrix renormalization group based method for adiabatically inserting flux, we discover a FQHE in a spin-½ isotropic kagome Heisenberg model. We identify this FQHE state as the long-sought CSL with a uniform chiral order spontaneously breaking time reversal symmetry, which is uniquely characterized by the half-integer quantized topological Chern number protected by a robust excitation gap. The CSL is found to be at the neighbor of the previously identified Z2 spin liquid, which may lead to an exotic quantum phase transition between two gapped topological spin liquids.

  7. Spin-1 Ising model on tetrahedron recursive lattices: Exact results

    Science.gov (United States)

    Jurčišinová, E.; Jurčišin, M.

    2016-11-01

    We investigate the ferromagnetic spin-1 Ising model on the tetrahedron recursive lattices. An exact solution of the model is found in the framework of which it is shown that the critical temperatures of the second order phase transitions of the model are driven by a single equation simultaneously on all such lattices. It is also shown that this general equation for the critical temperatures is equivalent to the corresponding polynomial equation for the model on the tetrahedron recursive lattice with arbitrary given value of the coordination number. The explicit form of these polynomial equations is shown for the lattices with the coordination numbers z = 6, 9, and 12. In addition, it is shown that the thermodynamic properties of all possible physical phases of the model are also completely driven by the corresponding single equations simultaneously on all tetrahedron recursive lattices. In this respect, the spontaneous magnetization, the free energy, the entropy, and the specific heat of the model are studied in detail.

  8. Toward an Ising model of cancer and beyond.

    Science.gov (United States)

    Torquato, Salvatore

    2011-02-01

    The holy grail of tumor modeling is to formulate theoretical and computational tools that can be utilized in the clinic to predict neoplastic progression and propose individualized optimal treatment strategies to control cancer growth. In order to develop such a predictive model, one must account for the numerous complex mechanisms involved in tumor growth. Here we review the research work that we have done toward the development of an 'Ising model' of cancer. The Ising model is an idealized statistical-mechanical model of ferromagnetism that is based on simple local-interaction rules, but nonetheless leads to basic insights and features of real magnets, such as phase transitions with a critical point. The review begins with a description of a minimalist four-dimensional (three dimensions in space and one in time) cellular automaton (CA) model of cancer in which cells transition between states (proliferative, hypoxic and necrotic) according to simple local rules and their present states, which can viewed as a stripped-down Ising model of cancer. This model is applied to study the growth of glioblastoma multiforme, the most malignant of brain cancers. This is followed by a discussion of the extension of the model to study the effect on the tumor dynamics and geometry of a mutated subpopulation. A discussion of how tumor growth is affected by chemotherapeutic treatment, including induced resistance, is then described. We then describe how to incorporate angiogenesis as well as the heterogeneous and confined environment in which a tumor grows in the CA model. The characterization of the level of organization of the invasive network around a solid tumor using spanning trees is subsequently discussed. Then, we describe open problems and future promising avenues for future research, including the need to develop better molecular-based models that incorporate the true heterogeneous environment over wide range of length and time scales (via imaging data), cell motility

  9. Nonequilibrium relaxation study of Ising spin glass models

    Science.gov (United States)

    Ozeki, Yukiyasu; Ito, Nobuyasu

    2001-07-01

    As an analysis of equilibrium phase transitions, the nonequilibrium relaxation method is extended to the spin glass (SG) transition. The +/-J Ising SG model is analyzed for three-dimensional (cubic) lattices up to the linear size of L=127 and for four-dimensional (hypercubic) lattice up to L=41. These sizes of systems are quite large as compared with those calculated, so far, by equilibrium simulations. As a dynamical order parameter, we calculate the clone correlation function (CCF) Q(t,tw)≡[F], which is a spin correlation of two replicas produced after the waiting time tw from a simple starting state. It is found that the CCF shows an exponential decay in the paramagnetic phase, and a power-law decay after aginglike development (t>>tw) in the SG phase. This provides a reliable upper bound of the transition temperature Tg. It is also found that a scaling relation, Q(t,tw)=t-λqwq¯(t/tw), holds just around the transition point providing the lower bound of Tg. Together with these two bounds, we propose a new dynamical way for the estimation of Tg from much larger systems. In the SG phase, the power-law behavior of the CCF for t>>tw suggests that the SG phase in short-range Ising models has a rugged phase space.

  10. Quantum dimensions from local operator excitations in the Ising model

    Science.gov (United States)

    Caputa, Paweł; Rams, Marek M.

    2017-02-01

    We compare the time evolution of entanglement measures after local operator excitation in the critical Ising model with predictions from conformal field theory. For the spin operator and its descendants we find that Rényi entropies of a block of spins increase by a constant that matches the logarithm of the quantum dimension of the conformal family. However, for the energy operator we find a small constant contribution that differs from the conformal field theory answer equal to zero. We argue that the mismatch is caused by the subtleties in the identification between the local operators in conformal field theory and their lattice counterpart. Our results indicate that evolution of entanglement measures in locally excited states not only constraints this identification, but also can be used to extract non-trivial data about the conformal field theory that governs the critical point. We generalize our analysis to the Ising model away from the critical point, states with multiple local excitations, as well as the evolution of the relative entropy after local operator excitation and discuss universal features that emerge from numerics.

  11. Block renormalization study on the nonequilibrium chiral Ising model.

    Science.gov (United States)

    Kim, Mina; Park, Su-Chan; Noh, Jae Dong

    2015-01-01

    We present a numerical study on the ordering dynamics of a one-dimensional nonequilibrium Ising spin system with chirality. This system is characterized by a direction-dependent spin update rule. Pairs of +- spins can flip to ++ or -- with probability (1-u) or to -+ with probability u while -+ pairs are frozen. The system was found to evolve into the ferromagnetic ordered state at any urenormalization analysis proposed by Basu and Hinrichsen [U. Basu and H. Hinrichsen, J. Stat. Mech.: Theor. Exp. (2011)]. The block renormalization method predicts, under the assumption of dynamic scale invariance, a scaling relation that can be used to estimate the scaling exponent numerically. We find the condition under which the scaling relation is justified. We then apply the method to our model and obtain the critical exponent zδ at several values of u. The numerical result is in perfect agreement with that of the previous study. This study serves as additional evidence for the claim that the nonequilibrium chiral Ising model displays power-law scaling behavior with continuously varying exponents.

  12. A Direct Calculation of Critical Exponents of Two-Dimensional Anisotropic Ising Model

    Institute of Scientific and Technical Information of China (English)

    XIONG Gang; WANG Xiang-Rong

    2006-01-01

    Using an exact solution of the one-dimensional quantum transverse-field Ising model, we calculate the critical exponents of the two-dimensional anisotropic classicalIsing model (IM). We verify that the exponents are the same as those of isotropic classical IM. Our approach provides an alternative means of obtaining and verifying these well-known results.

  13. Computer simulation of temperature-dependent growth of fractal and compact domains in diluted Ising models

    DEFF Research Database (Denmark)

    Sørensen, Erik Schwartz; Fogedby, Hans C.; Mouritsen, Ole G.

    1989-01-01

    A version of the two-dimensional site-diluted spin-(1/2 Ising model is proposed as a microscopic interaction model which governs solidification and growth processes controlled by vacancy diffusion. The Ising Hamiltonian describes a solid-fluid phase transition and it permits a thermodynamic......-water interfaces....

  14. Conformal symmetry of the critical 3D Ising model inside a sphere

    CERN Document Server

    Cosme, Catarina; Penedones, Joao

    2015-01-01

    We perform Monte-Carlo simulations of the three-dimensional Ising model at the critical temperature and zero magnetic field. We simulate the system in a ball with free boundary conditions on the two dimensional spherical boundary. Our results for one and two point functions in this geometry are consistent with the predictions from the conjectured conformal symmetry of the critical Ising model.

  15. Nonequilibrium stationary states and phase transitions in directed Ising models

    Science.gov (United States)

    Godrèche, Claude; Bray, Alan J.

    2009-12-01

    We study the nonequilibrium properties of directed Ising models with non-conserved dynamics, in which each spin is influenced by only a subset of its nearest neighbours. We treat the following models: (i) the one-dimensional chain; (ii) the two-dimensional square lattice; (iii) the two-dimensional triangular lattice and (iv) the three-dimensional cubic lattice. We raise and answer the question: (a) under what conditions is the stationary state described by the equilibrium Boltzmann-Gibbs distribution? We show that, for models (i), (ii) and (iii), in which each spin 'sees' only half of its neighbours, there is a unique set of transition rates, namely with exponential dependence in the local field, for which this is the case. For model (iv), we find that any rates satisfying the constraints required for the stationary measure to be Gibbsian should satisfy detailed balance, ruling out the possibility of directed dynamics. We finally show that directed models on lattices of coordination number z>=8 with exponential rates cannot accommodate a Gibbsian stationary state. We conjecture that this property extends to any form of the rates. We are thus led to the conclusion that directed models with Gibbsian stationary states only exist in dimensions one and two. We then raise the question: (b) do directed Ising models, augmented by Glauber dynamics, exhibit a phase transition to a ferromagnetic state? For the models considered above, the answers are open problems, with the exception of the simple cases (i) and (ii). For Cayley trees, where each spin sees only the spins further from the root, we show that there is a phase transition provided the branching ratio, q, satisfies q>=3.

  16. The Gonihedric Paradigm Extensions of the Ising Model

    CERN Document Server

    Savvidy, George

    2015-01-01

    We suggest a generalization of the Feynman path integral to an integral over random surfaces. The proposed action is proportional to the linear size of the random surfaces and is called gonihedric. The convergence and the properties of the partition function are analysed. The model can also be formulated as a spin system with identical partition function. The spin system represents a generalisation of the Ising model with ferromagnetic, antiferromagnetic and quartic interactions. Higher symmetry of the model allows to construct dual spin systems in three and four dimensions. In three dimensions the transfer matrix describes the propagation of closed loops and we found its exact spectrum. It is a unique exact solution of the tree-dimensional statistical spin system. In three and four dimensions the system exhibits the second order phase transitions. The gonihedric spin systems have exponentially degenerated vacuum states separated by the potential barriers and can be used as a storage of binary information.

  17. Antiferromagnetic Ising model in an imaginary magnetic field

    Science.gov (United States)

    Azcoiti, Vicente; Di Carlo, Giuseppe; Follana, Eduardo; Royo-Amondarain, Eduardo

    2017-09-01

    We study the two-dimensional antiferromagnetic Ising model with a purely imaginary magnetic field, which can be thought of as a toy model for the usual θ physics. Our motivation is to have a benchmark calculation in a system which suffers from a strong sign problem, so that our results can be used to test Monte Carlo methods developed to tackle such problems. We analyze here this model by means of analytical techniques, computing exactly the first eight cumulants of the expansion of the effective Hamiltonian in powers of the inverse temperature, and calculating physical observables for a large number of degrees of freedom with the help of standard multiprecision algorithms. We report accurate results for the free energy density, internal energy, standard and staggered magnetization, and the position and nature of the critical line, which confirm the mean-field qualitative picture, and which should be quantitatively reliable, at least in the high-temperature regime, including the entire critical line.

  18. Topological Phases of Interacting Bosons on the Kagome Lattice

    Science.gov (United States)

    Roychowdhury, Krishanu; Bhattacharjee, Subhro; Pollmann, Frank

    2015-03-01

    We consider an extended Hubbard model of hard core bosons including nearest-neighbour hopping and long range repulsive interactions on a kagome lattice. The system is an insulator at commensurate fillings of 1/6, 1/3 and 1/2 and can be mapped to different dimer models on the triangular lattice (depending on the filling). We focus on the filling of 1/3, which transforms to a fully packed loop (FPL) model, and derive the full phase diagram in the low-energy subspace. Similar to the quantum dimer model and easy-axis kagome antiferromagnetic model studied before, we find an extended region of a gapped Z2 liquid with vison excitations. The gauge fluctuations, responsible for the vison modes, are dictated by the action of an even Ising gauge theory. In the ordered phase, where the vison gap closes, we observe a 3-fold rotationally symmetric loop ordering and present the critical theory for the amplitude fluctuations of the condensed modes. We also speculate the phase diagram for the fermionic counterpart of the model at all the above mentioned fractional fillings.

  19. Propagation of fluctuations in the quantum Ising model

    Science.gov (United States)

    Navez, P.; Tsironis, G. P.; Zagoskin, A. M.

    2017-02-01

    We investigate entanglement dynamics and correlations in the quantum Ising model in arbitrary dimensions using a large-coordination-number expansion. We start from the pure paramagnetic regime obtained through zero spin-spin coupling and subsequently turn on the interspin interaction in a time-dependent fashion. We investigate analytically and compare results for both the slow adiabatic onset of the interactions and the fast instantaneous switching. We find that in the latter case of an initial excitation mode a quantum correlation wave spreads through the system, propagating with twice the group velocity of the linearized equilibrium modes. This wave establishes the spatiotemporal regime of entangled quantum properties of the system for time scales shorter than the decoherence time and thus provides an indicator for the "quantumness" of the physical system that the specific system models.

  20. Modeling dark energy through an Ising fluid with network interactions

    CERN Document Server

    Luongo, Orlando

    2013-01-01

    We show that the dark energy effects can be modeled by using an \\emph{Ising perfect fluid} with network interactions, whose low redshift equation of state, i.e. $\\omega_0$, becomes $\\omega_0=-1$ as in the $\\Lambda$CDM model. In our picture, dark energy is characterized by a barotropic fluid on a lattice in the equilibrium configuration. Thus, mimicking the spin interaction by replacing the spin variable with an occupational number, the pressure naturally becomes negative. We find that the corresponding equation of state mimics the effects of a variable dark energy term, whose limiting case reduces to the cosmological constant $\\Lambda$. This permits us to avoid the introduction of a vacuum energy as dark energy source by hand, alleviating the coincidence and fine tuning problems. We find fairly good cosmological constraints, by performing three tests with supernovae Ia, baryonic acoustic oscillation and cosmic microwave background measurements. Finally, we perform the AIC and BIC selection criteria, showing t...

  1. Ising model with short-range correlated dilution

    Science.gov (United States)

    Branco, N. S.; de Queiroz, S. L. A.; Dos Santos, Raimundo R.

    1988-07-01

    We consider a diluted Ising model in which the absence of a spin affects the exchange coupling of a nearest-neighbor pair along the line joining the three spins; that is, it aquires the value αJ, where α is a phenomenological parameter ɛ[0,1]. This model has been proposed to explain the experimental phase diagram for KNixMg1-xF3. A position-space renormalization-group analysis clearly distinguishes two percolation thresholds depending on whether α=0 or α>0, though both cases seem to be in the same universality class. Further, thermal fluctuations dominate over the geometrical ones as in the uncorrelated case and the critical curve (critical temperature versus concentration of magnetic sites) displays an upward curvature for intermediate degrees of correlation 0<α<1, as experimentally observed.

  2. Localized structures in Kagome lattices

    Energy Technology Data Exchange (ETDEWEB)

    Saxena, Avadh B [Los Alamos National Laboratory; Bishop, Alan R [Los Alamos National Laboratory; Law, K J H [UNIV OF MASSACHUSETTS; Kevrekidis, P G [UNIV OF MASSACHUSETTS

    2009-01-01

    We investigate the existence and stability of gap vortices and multi-pole gap solitons in a Kagome lattice with a defocusing nonlinearity both in a discrete case and in a continuum one with periodic external modulation. In particular, predictions are made based on expansion around a simple and analytically tractable anti-continuum (zero coupling) limit. These predictions are then confirmed for a continuum model of an optically-induced Kagome lattice in a photorefractive crystal obtained by a continuous transformation of a honeycomb lattice.

  3. Variational Monte Carlo study of a chiral spin liquid in the extended Heisenberg model on the kagome lattice

    Science.gov (United States)

    Hu, Wen-Jun; Zhu, Wei; Zhang, Yi; Gong, Shoushu; Becca, Federico; Sheng, D. N.

    2015-01-01

    We investigate the extended Heisenberg model on the kagome lattice by using Gutzwiller projected fermionic states and the variational Monte Carlo technique. In particular, when both second- and third-neighbor superexchanges are considered, we find that a gapped spin liquid described by nontrivial magnetic fluxes and long-range chiral-chiral correlations is energetically favored compared to the gapless U(1) Dirac state. Furthermore, the topological Chern number, obtained by integrating the Berry curvature, and the degeneracy of the ground state, by constructing linearly independent states, lead us to identify this flux state as the chiral spin liquid with a C =1 /2 fractionalized Chern number.

  4. Robust criticality of Ising model on rewired directed networks

    CERN Document Server

    Lipowski, Adam; Lipowska, Dorota

    2015-01-01

    We show that preferential rewiring, which is supposed to mimick the behaviour of financial agents, changes a directed-network Ising ferromagnet with a single critical point into a model with robust critical behaviour. For the non-rewired random graph version, due to a constant number of links out-going from each site, we write a simple mean-field-like equation describing the behaviour of magnetization; we argue that it is exact and support the claim with extensive Monte Carlo simulations. For the rewired version, this equation is obeyed only at low temperatures. At higher temperatures, rewiring leads to strong heterogeneities, which apparently invalidates mean-field arguments and induces large fluctuations and divergent susceptibility. Such behaviour is traced back to the formation of a relatively small core of agents which influence the entire system.

  5. Magnetic critical behavior of the Ising model on fractal structures

    Science.gov (United States)

    Monceau, Pascal; Perreau, Michel; Hébert, Frédéric

    1998-09-01

    The critical temperature and the set of critical exponents (β,γ,ν) of the Ising model on a fractal structure, namely the Sierpiński carpet, are calculated from a Monte Carlo simulation based on the Wolff algorithm together with the histogram method and finite-size scaling. Both cases of periodic boundary conditions and free edges are investigated. The calculations have been done up to the seventh iteration step of the fractal structure. The results show that, although the structure is not translationally invariant, the scaling behavior of thermodynamical quantities is conserved, which gives a meaning to the finite-size analysis. Although some discrepancies in the values of the critical exponents occur between periodic boundary conditions and free edges, the effective dimension obtained through the Rushbrooke and Josephson's scaling law have the same value in both cases. This value is slightly but significantly different from the fractal dimension.

  6. Maximum caliber inference and the stochastic Ising model

    Science.gov (United States)

    Cafaro, Carlo; Ali, Sean Alan

    2016-11-01

    We investigate the maximum caliber variational principle as an inference algorithm used to predict dynamical properties of complex nonequilibrium, stationary, statistical systems in the presence of incomplete information. Specifically, we maximize the path entropy over discrete time step trajectories subject to normalization, stationarity, and detailed balance constraints together with a path-dependent dynamical information constraint reflecting a given average global behavior of the complex system. A general expression for the transition probability values associated with the stationary random Markov processes describing the nonequilibrium stationary system is computed. By virtue of our analysis, we uncover that a convenient choice of the dynamical information constraint together with a perturbative asymptotic expansion with respect to its corresponding Lagrange multiplier of the general expression for the transition probability leads to a formal overlap with the well-known Glauber hyperbolic tangent rule for the transition probability for the stochastic Ising model in the limit of very high temperatures of the heat reservoir.

  7. Testing Lorentz Invariance Emergence in the Ising Model using Monte Carlo simulations

    CERN Document Server

    Dias Astros, Maria Isabel

    2017-01-01

    In the context of the Lorentz invariance as an emergent phenomenon at low energy scales to study quantum gravity a system composed by two 3D interacting Ising models (one with an anisotropy in one direction) was proposed. Two Monte Carlo simulations were run: one for the 2D Ising model and one for the target model. In both cases the observables (energy, magnetization, heat capacity and magnetic susceptibility) were computed for different lattice sizes and a Binder cumulant introduced in order to estimate the critical temperature of the systems. Moreover, the correlation function was calculated for the 2D Ising model.

  8. Completeness of the classical 2D Ising model and universal quantum computation.

    Science.gov (United States)

    Van den Nest, M; Dür, W; Briegel, H J

    2008-03-21

    We prove that the 2D Ising model is complete in the sense that the partition function of any classical q-state spin model (on an arbitrary graph) can be expressed as a special instance of the partition function of a 2D Ising model with complex inhomogeneous couplings and external fields. In the case where the original model is an Ising or Potts-type model, we find that the corresponding 2D square lattice requires only polynomially more spins with respect to the original one, and we give a constructive method to map such models to the 2D Ising model. For more general models the overhead in system size may be exponential. The results are established by connecting classical spin models with measurement-based quantum computation and invoking the universality of the 2D cluster states.

  9. The boundary states and correlation functions of the tricritical Ising model

    CERN Document Server

    Balaska, S

    2006-01-01

    We consider the minimal model describing the tricritical Ising model on the upper half plane or equivalently on an infinite strip of finite width and we determine its consistents boundary states as well as its 1-point correlation functions.

  10. The exact interface model for wetting in the two-dimensional Ising model

    OpenAIRE

    Upton, P. J.

    2002-01-01

    We use exact methods to derive an interface model from an underlying microscopic model, i.e., the Ising model on a square lattice. At the wetting transition in the two-dimensional Ising model, the long Peierls contour (or interface) gets depinned from the substrate. Using exact transfer-matrix methods, we find that on sufficiently large length scales (i.e., length scales sufficiently larger than the bulk correlation length) the distribution of the long contour is given by a unique probability...

  11. A Kagome Map of Spin Liquidsx

    Science.gov (United States)

    Essafi, Karim; Benton, Owen; Jaubert, Ludovic D. C.

    Competing interactions in frustrated magnets prevent ordering down to very low temperatures and stabilize exotic highly degenerate phases where strong correlations coexist with fluctuations. We study a very general nearest-neighbour Heisenberg spin model Hamiltonian on the kagome lattice which consist of Dzyaloshinskii-Moriya, ferro- and antiferromagnetic interactions. We present a three-fold mapping which transforms the well-known Heisenberg antiferromagnet (HAF) and XXZ model onto two lines of time-reversal Hamiltonians. The mapping is exact for both classical and quantum spins, i.e. preserves the energy spectrums of the HAF and XXZ model. As a consequence, our three-fold mapping gives rise to a connected network of quantum spin liquids centered around the Ising antiferromagnet. We show that this quantum disorder spreads over an extended region of the phase diagram at linear order in spin wave theory, which overlaps with the parameter region of Herbertsmithite ZnCu3(OH)6Cl2. At the classical level, all the phases have an extensively degenerate ground-state which present a variety of properties such as ferromagnetically induced pinch points in the structure factor and spontaneous scalar chirality which was absent in the original HAF and XXZ models. This work was supported by the Okinawa Institute of Science and Technology Graduate University.

  12. The boson-Hubbard model on a kagome lattice with a sextic ring-exchange term

    Science.gov (United States)

    Rousseau, Valery; Tam, Ka-Ming; Moreno, Juana; Jarrell, Mark

    2012-02-01

    We present exact quantum Monte Carlo simulations of hard-core bosons in a two-dimensional Kagome lattice with a sextic ring-exchange term. We study how the superfluid density evolves as the ring-exchange interactions are increased. We show that the system becomes unstable in the limit of large interactions at all fillings and undergoes a phase separation, except at 13 and 23 fillings for which the superfluid density vanishes and a solid state forms.

  13. Elemental analysis and magnetism of hydronium jarosites-model kagome antiferromagnets and topological spin glasses

    Energy Technology Data Exchange (ETDEWEB)

    Wills, A S; Bisson, W G, E-mail: a.s.wills@ucl.ac.uk [Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ (United Kingdom)

    2011-04-27

    The jarosites are the most studied examples of kagome antiferromagnets. Research into them has inspired new directions in magnetism, such as the role of the Dzyaloshinsky-Moriya interaction in symmetry breaking, kagome spin ice, and whether spin glass-like phases can exist in the disorder-free limit. This last point is based around the observation of unconventional thermodynamic and kinetic responses in hydronium jarosite, H{sub 3}OFe{sub 3}(SO{sub 4}){sub 2}(OH){sub 6}, that have led to its classification as a 'topological' spin glass, reflecting the defining role that the underlying geometry of the kagome lattice plays in the formation of the spin glass state. In this paper we explore one of the fundamental questions concerning the frustrated magnetism in hydronium jarosite: whether the spin glass phase is the result of chemical disorder and concomitant randomness in the exchange interactions. Confirming previous crystallographic studies, we use elemental analysis to show that the nature of the low temperature magnetic state is not a simple function of chemical disorder and provide evidence to support the hypothesis that anisotropies drive the spin glass transition.

  14. Elemental analysis and magnetism of hydronium jarosites--model kagome antiferromagnets and topological spin glasses.

    Science.gov (United States)

    Wills, A S; Bisson, W G

    2011-04-27

    The jarosites are the most studied examples of kagome antiferromagnets. Research into them has inspired new directions in magnetism, such as the role of the Dzyaloshinsky-Moriya interaction in symmetry breaking, kagome spin ice, and whether spin glass-like phases can exist in the disorder-free limit. This last point is based around the observation of unconventional thermodynamic and kinetic responses in hydronium jarosite, H(3)OFe(3)(SO(4))(2)(OH)(6), that have led to its classification as a 'topological' spin glass, reflecting the defining role that the underlying geometry of the kagome lattice plays in the formation of the spin glass state. In this paper we explore one of the fundamental questions concerning the frustrated magnetism in hydronium jarosite: whether the spin glass phase is the result of chemical disorder and concomitant randomness in the exchange interactions. Confirming previous crystallographic studies, we use elemental analysis to show that the nature of the low temperature magnetic state is not a simple function of chemical disorder and provide evidence to support the hypothesis that anisotropies drive the spin glass transition.

  15. Half-metallicity of a kagome spin lattice: the case of a manganese bis-dithiolene monolayer.

    Science.gov (United States)

    Zhao, Mingwen; Wang, Aizhu; Zhang, Xiaoming

    2013-11-07

    The spin ordering in kagome lattices has long been studied in the search for real materials with a spin-liquid ground state. The synthesis of a nickel bis-dichiolene complex (Ni3C12S12) nanosheet (T. Kambe et al., J. Am. Chem. Soc., 2013, 135, 2462) paved a way for realizing real two-dimensional kagome lattices. Using first-principles calculations, we predicted that a ferromagnetic kagome spin lattice with S = 3/2 on lattice vertices can be achieved in an Mn3C12S12 monolayer formed by substituting Ni with Mn atoms in nonmagnetic Ni3C12S12. Monte Carlo simulations on the basis of the Ising model suggest that it has a Curie temperature of about 212 K. A ferromagnetic Mn3C12S12 monolayer is half metallic with high carrier mobility in one spin channel and a band gap of 1.54 eV in another spin channel, which is quite promising for spintronic device applications. Additionally, a small band gap opens up at the Dirac point of the kagome bands due to the spin-orbital coupling effects, which may be implementable for achieving a quantum anomalous Hall effect.

  16. Low temperature expansion of the gonihedric Ising model

    CERN Document Server

    Pietig, R

    1998-01-01

    We investigate a model of closed $(d-1)$-dimensional soft-self-avoiding random surfaces on a $d$-dimensional cubic lattice. The energy of a surface configuration is given by $E=J(n_{2}+4k n_{4})$, where $n_{2}$ is the number of edges, where two plaquettes meet at a right angle and $n_{4}$ is the number of edges, where 4 plaquettes meet. This model can be represented as a next-nearest-neighbour- and plaquette-interaction. It corresponds to a special case of a general class of spin systems introduced by Wegner and Savvidy. Since there is no term proportional to the surface area, the bare surface tension of the model vanishes, in contrast to the ordinary Ising model. By a suitable adaption of Peierls argument, we prove the existence of infinitely many ordered low temperature phases for the case $k=0$. A low temperature expansion of the free energy in 3 dimensions up to order $x^{38}$ ($x={e}^{-\\beta J}$) shows, that for $k>0$ only the ferromagnetic low temperature phases remain stable. An analysis of low tempera...

  17. Maximum likelihood reconstruction for Ising models with asynchronous updates

    CERN Document Server

    Zeng, Hong-Li; Aurell, Erik; Hertz, John; Roudi, Yasser

    2012-01-01

    We describe how the couplings in a non-equilibrium Ising model can be inferred from observing the model history. Two cases of an asynchronous update scheme are considered: one in which we know both the spin history and the update times (times at which an attempt was made to flip a spin) and one in which we only know the spin history (i.e., the times at which spins were actually flipped). In both cases, maximizing the likelihood of the data leads to exact learning rules for the couplings in the model. For the first case, we show that one can average over all possible choices of update times to obtain a learning rule that depends only on spin correlations and not on the specific spin history. For the second case, the same rule can be derived within a further decoupling approximation. We study all methods numerically for fully asymmetric Sherrington-Kirkpatrick models, varying the data length, system size, temperature, and external field. Good convergence is observed in accordance with the theoretical expectatio...

  18. Artificial kagome arrays of nanomagnets: a frozen dipolar spin ice.

    Science.gov (United States)

    Rougemaille, N; Montaigne, F; Canals, B; Duluard, A; Lacour, D; Hehn, M; Belkhou, R; Fruchart, O; El Moussaoui, S; Bendounan, A; Maccherozzi, F

    2011-02-04

    Magnetic frustration effects in artificial kagome arrays of nanomagnets are investigated using x-ray photoemission electron microscopy and Monte Carlo simulations. Spin configurations of demagnetized networks reveal unambiguous signatures of long range, dipolar interaction between the nanomagnets. As soon as the system enters the spin ice manifold, the kagome dipolar spin ice model captures the observed physics, while the short range kagome spin ice model fails.

  19. Artificial Kagome Arrays of Nanomagnets: A Frozen Dipolar Spin Ice

    OpenAIRE

    Rougemaille, N.; Montaigne, F.; Canals, B.; Duluard, A.; D. Lacour; Hehn, M.; Belkhou, R.; Fruchart, O.; Moussaoui, S. El; Bendounan, A.; Maccherozzi, F.

    2011-01-01

    Magnetic frustration effects in artificial kagome arrays of nanomagnets are investigated using x-ray photoemission electron microscopy and Monte Carlo simulations. Spin configurations of demagnetized networks reveal unambiguous signatures of long range, dipolar interaction between the nanomagnets. As soon as the system enters the spin ice manifold, the kagome dipolar spin ice model captures the observed physics, while the short range kagome spin ice model fails.

  20. Inhomogeneous and Self-Organized Temperature in Schelling-Ising Model

    Science.gov (United States)

    Müller, Katharina; Schulze, Christian; Stauffer, Dietrich

    The Schelling model of 1971 is a complicated version of a square-lattice Ising model at zero temperature, to explain urban segregation, based on the neighbor preferences of the residents, without external reasons. Various versions between Ising and Schelling models give about the same results. Inhomogeneous "temperatures" T do not change the results much, while a feedback between segregation and T leads to a self-organization of an average T.

  1. Universality class of the two-dimensional site-diluted Ising model.

    Science.gov (United States)

    Martins, P H L; Plascak, J A

    2007-07-01

    In this work, we evaluate the probability distribution function of the order parameter for the two-dimensional site-diluted Ising model. Extensive Monte Carlo simulations have been performed for different spin concentrations p (0.70universality class of the diluted Ising model seems to be independent of the amount of dilution. Logarithmic corrections of the finite-size critical temperature behavior of the model can also be inferred even for such small lattices.

  2. Ising percolation in a three-state majority vote model

    Science.gov (United States)

    Balankin, Alexander S.; Martínez-Cruz, M. A.; Gayosso Martínez, Felipe; Mena, Baltasar; Tobon, Atalo; Patiño-Ortiz, Julián; Patiño-Ortiz, Miguel; Samayoa, Didier

    2017-02-01

    In this Letter, we introduce a three-state majority vote model in which each voter adopts a state of a majority of its active neighbors, if exist, but the voter becomes uncommitted if its active neighbors are in a tie, or all neighbors are the uncommitted. Numerical simulations were performed on square lattices of different linear size with periodic boundary conditions. Starting from a random distribution of active voters, the model leads to a stable non-consensus state in which three opinions coexist. We found that the "magnetization" of the non-consensus state and the concentration of uncommitted voters in it are governed by an initial composition of system and are independent of the lattice size. Furthermore, we found that a configuration of the stable non-consensus state undergoes a second order percolation transition at a critical concentration of voters holding the same opinion. Numerical simulations suggest that this transition belongs to the same universality class as the Ising percolation. These findings highlight the effect of an updating rule for a tie between voter neighbors on the critical behavior of models obeying the majority vote rule whenever a strict majority exists.

  3. Differential geometry of the space of Ising models

    Science.gov (United States)

    Machta, Benjamin; Chachra, Ricky; Transtrum, Mark; Sethna, James

    2012-02-01

    We use information geometry to understand the emergence of simple effective theories, using an Ising model perturbed with terms coupling non-nearest-neighbor spins as an example. The Fisher information is a natural metric of distinguishability for a parameterized space of probability distributions, applicable to models in statistical physics. Near critical points both the metric components (four-point susceptibilities) and the scalar curvature diverge with corresponding critical exponents. However, connections to Renormalization Group (RG) ideas have remained elusive. Here, rather than looking at RG flows of parameters, we consider the reparameterization-invariant flow of the manifold itself. To do this we numerically calculate the metric in the original parameters, taking care to use only information available after coarse-graining. We show that under coarse-graining the metric contracts very anisotropically, leading to a ``sloppy'' spectrum with the metric's Eigenvalues spanning many orders of magnitude. Our results give a qualitative explanation for the success of simple models: most directions in parameter space become fundamentally indistinguishable after coarse-graining.

  4. Modeling Dark Energy Through AN Ising Fluid with Network Interactions

    Science.gov (United States)

    Luongo, Orlando; Tommasini, Damiano

    2014-12-01

    We show that the dark energy (DE) effects can be modeled by using an Ising perfect fluid with network interactions, whose low redshift equation of state (EoS), i.e. ω0, becomes ω0 = -1 as in the ΛCDM model. In our picture, DE is characterized by a barotropic fluid on a lattice in the equilibrium configuration. Thus, mimicking the spin interaction by replacing the spin variable with an occupational number, the pressure naturally becomes negative. We find that the corresponding EoS mimics the effects of a variable DE term, whose limiting case reduces to the cosmological constant Λ. This permits us to avoid the introduction of a vacuum energy as DE source by hand, alleviating the coincidence and fine tuning problems. We find fairly good cosmological constraints, by performing three tests with supernovae Ia (SNeIa), baryonic acoustic oscillation (BAO) and cosmic microwave background (CMB) measurements. Finally, we perform the Akaike information criterion (AIC) and Bayesian information criterion (BIC) selection criteria, showing that our model is statistically favored with respect to the Chevallier-Polarsky-Linder (CPL) parametrization.

  5. Theory of quantum kagome ice and vison zero modes

    Science.gov (United States)

    Huang, Yi-Ping; Hermele, Michael

    2017-02-01

    We derive an effective Z2 gauge theory to describe the quantum kagome ice (QKI) state that has been observed by Carrasquilla et al. [Nat. Commun. 6, 7421 (2015), 10.1038/ncomms8421] in Monte Carlo studies of the S =1/2 kagome XYZ model in a Zeeman field. The numerical results on QKI are consistent with, but do not confirm or rule out, the hypothesis that it is a Z2 spin liquid. Our effective theory allows us to explore this hypothesis and make a striking prediction for future numerical studies, namely, that symmetry-protected vison zero modes arise at lattice disclination defects, leading to a Curie defect term in the spin susceptibility, and a characteristic (Ndis-1 )ln2 contribution to the entropy, where Ndis is the number of disclinations. Only the Z2 Ising symmetry is required to protect the vison zero modes. This is remarkable because a unitary Z2 symmetry cannot be responsible for symmetry-protected degeneracies of local degrees of freedom. We also discuss other signatures of symmetry fractionalization in the Z2 spin liquid, and phase transitions out of the Z2 spin liquid to nearby ordered phases.

  6. Large-scale Monte Carlo simulations for the depinning transition in Ising-type lattice models

    Science.gov (United States)

    Si, Lisha; Liao, Xiaoyun; Zhou, Nengji

    2016-12-01

    With the developed "extended Monte Carlo" (EMC) algorithm, we have studied the depinning transition in Ising-type lattice models by extensive numerical simulations, taking the random-field Ising model with a driving field and the driven bond-diluted Ising model as examples. In comparison with the usual Monte Carlo method, the EMC algorithm exhibits greater efficiency of the simulations. Based on the short-time dynamic scaling form, both the transition field and critical exponents of the depinning transition are determined accurately via the large-scale simulations with the lattice size up to L = 8912, significantly refining the results in earlier literature. In the strong-disorder regime, a new universality class of the Ising-type lattice model is unveiled with the exponents β = 0.304(5) , ν = 1.32(3) , z = 1.12(1) , and ζ = 0.90(1) , quite different from that of the quenched Edwards-Wilkinson equation.

  7. Two-Dimensional Saddle Point Equation of Ginzburg-Landau Hamiltonian for the Diluted Ising Model

    Institute of Scientific and Technical Information of China (English)

    WU Xin-Tian

    2006-01-01

    @@ The saddle point equation of Ginzburg-Landau Hamiltonian for the diluted Ising model is developed. The ground state is solved numerically in two dimensions. The result is partly explained by the coarse-grained approximation.

  8. Topological defects on the lattice: I. The Ising model

    Science.gov (United States)

    Aasen, David; Mong, Roger S. K.; Fendley, Paul

    2016-09-01

    In this paper and its sequel, we construct topologically invariant defects in two-dimensional classical lattice models and quantum spin chains. We show how defect lines commute with the transfer matrix/Hamiltonian when they obey the defect commutation relations, cousins of the Yang-Baxter equation. These relations and their solutions can be extended to allow defect lines to branch and fuse, again with properties depending only on topology. In this part I, we focus on the simplest example, the Ising model. We define lattice spin-flip and duality defects and their branching, and prove they are topological. One useful consequence is a simple implementation of Kramers-Wannier duality on the torus and higher genus surfaces by using the fusion of duality defects. We use these topological defects to do simple calculations that yield exact properties of the conformal field theory describing the continuum limit. For example, the shift in momentum quantization with duality-twisted boundary conditions yields the conformal spin 1/16 of the chiral spin field. Even more strikingly, we derive the modular transformation matrices explicitly and exactly.

  9. Excited TBA equations I: Massive tricritical Ising model

    Energy Technology Data Exchange (ETDEWEB)

    Pearce, Paul A. E-mail: p.pearce@ms.unimelb.edu.au; Chim, Leung E-mail: leung.chim@dsto.defence.gov.au; Ahn, Changrim E-mail: ahn@dante.ewha.ac.kr

    2001-05-14

    We consider the massive tricritical Ising model M(4,5) perturbed by the thermal operator phi (cursive,open) Greek{sub 1,3} in a cylindrical geometry and apply integrable boundary conditions, labelled by the Kac labels (r,s), that are natural off-critical perturbations of known conformal boundary conditions. We derive massive thermodynamic Bethe ansatz (TBA) equations for all excitations by solving, in the continuum scaling limit, the TBA functional equation satisfied by the double-row transfer matrices of the A{sub 4} lattice model of Andrews, Baxter and Forrester (ABF) in Regime III. The complete classification of excitations, in terms of (m,n) systems, is precisely the same as at the conformal tricritical point. Our methods also apply on a torus but we first consider (r,s) boundaries on the cylinder because the classification of states is simply related to fermionic representations of single Virasoro characters {chi}{sub r,s}(q). We study the TBA equations analytically and numerically to determine the conformal UV and free particle IR spectra and the connecting massive flows. The TBA equations in Regime IV and massless RG flows are studied in Part II.

  10. Direct Monte Carlo Measurement of the Surface Tension in Ising Models

    CERN Document Server

    Hasenbusch, M

    1992-01-01

    I present a cluster Monte Carlo algorithm that gives direct access to the interface free energy of Ising models. The basic idea is to simulate an ensemble that consists of both configurations with periodic and with antiperiodic boundary conditions. A cluster algorithm is provided that efficently updates this joint ensemble. The interface tension is obtained from the ratio of configurations with periodic and antiperiodic boundary conditions, respectively. The method is tested for the 3-dimensional Ising model.

  11. Polychromatic Arm Exponents for the Critical Planar FK-Ising model

    OpenAIRE

    Wu, Hao

    2016-01-01

    We derive the arm exponents of SLE$_{\\kappa}$ for $\\kappa\\in (4,8)$ and explain how to combine them with the convergence of the interface to obtain the arm exponents of critical FK-Ising model. We obtain six different patterns of boundary arm exponents and three different patterns of interior arm exponents of the critical planar FK-Ising model on the square lattice.

  12. Phase transitions and relaxation dynamics of Ising models exchanging particles

    Science.gov (United States)

    Goh, Segun; Fortin, Jean-Yves; Choi, M. Y.

    2017-01-01

    A variety of systems in nature and in society are open and subject to exchanging their constituents with other systems (e.g., environments). For instance, in biological systems, cells collect necessary energy and material by exchange of molecules or ions. Similarly, countries, cities or research institutes evolve as their constituents move in or out. To probe the corresponding particle exchange dynamics in such systems, we consider two Ising models exchanging particles and establish a master equation describing the equilibrium phases as well as the non-equilibrium dynamics of the system. It is found that an additional stable phase emerges as a consequence of the particle exchange process. Furthermore, we formulate the Ginzburg-Landau theory which allows to probe correlation effects. Accordingly, critical slowing down is manifested and the associated dynamic exponent is computed in the linear relaxation regime. In particular, this approach is relevant for investigating the grand canonical description of the system plus environment, with particle exchange and state transitions taken into account explicitly.

  13. Hysteresis of the Magnetic Particle in a Dipolar Ising Model

    Institute of Scientific and Technical Information of China (English)

    WU Yin-Zhong; LI Zhen-Ya

    2002-01-01

    Zero-temperature Monte Carlo simulations are used to investigate the hysteresis of a magnetic particle ina dipolarIsing model. The magnetic particle is described in a system of permanent dipoles, and the dipoles are locatedin a cubic lattice site. The effects of the shape and the size of the particle on the hysteresis loop at zero temperatureare obtained. For strong exchange interactions, the shapes of magnetic hysteresis loops approach rectangle. For weakexchange interactions, the effects of the size and the shape of the particle on the loops are more remarkable than thoseof strong exchange interactions case. The slope of the hysteresis loop decreases with the increase of the ratio of thesemi major axis to the semi minor axis of the ellipsoidal magnetic particle, and there is an increase of the slope of thehysteresis with the decrease of the size of the magnetic particle. The effects of the shape and size of the particle on thecoercive force at zero temperature are also investigated.

  14. Monte Carlo tests of renormalization-group predictions for critical phenomena in Ising models

    Science.gov (United States)

    Binder, Kurt; Luijten, Erik

    2001-04-01

    A critical review is given of status and perspectives of Monte Carlo simulations that address bulk and interfacial phase transitions of ferromagnetic Ising models. First, some basic methodological aspects of these simulations are briefly summarized (single-spin flip vs. cluster algorithms, finite-size scaling concepts), and then the application of these techniques to the nearest-neighbor Ising model in d=3 and 5 dimensions is described, and a detailed comparison to theoretical predictions is made. In addition, the case of Ising models with a large but finite range of interaction and the crossover scaling from mean-field behavior to the Ising universality class are treated. If one considers instead a long-range interaction described by a power-law decay, new classes of critical behavior depending on the exponent of this power law become accessible, and a stringent test of the ε-expansion becomes possible. As a final type of crossover from mean-field type behavior to two-dimensional Ising behavior, the interface localization-delocalization transition of Ising films confined between “competing” walls is considered. This problem is still hampered by questions regarding the appropriate coarse-grained model for the fluctuating interface near a wall, which is the starting point for both this problem and the theory of critical wetting.

  15. Bipartition Polynomials, the Ising Model, and Domination in Graphs

    Directory of Open Access Journals (Sweden)

    Dod Markus

    2015-05-01

    Full Text Available This paper introduces a trivariate graph polynomial that is a common generalization of the domination polynomial, the Ising polynomial, the matching polynomial, and the cut polynomial of a graph. This new graph polynomial, called the bipartition polynomial, permits a variety of interesting representations, for instance as a sum ranging over all spanning forests. As a consequence, the bipartition polynomial is a powerful tool for proving properties of other graph polynomials and graph invariants. We apply this approach to show that, analogously to the Tutte polynomial, the Ising polynomial introduced by Andrén and Markström in [3], can be represented as a sum over spanning forests.

  16. Non-conventional Superconductors and diluted Ising Model

    CERN Document Server

    Ni, Xuan Zhong

    2016-01-01

    This paper demonstrates that the results of a Monte Carlo simulation of a diluted 2D Ising antiferromagnetic system corresponds with the phase diagram for non conventional superconductors. An energy gap of this system is defined. We also find a strange phenomenon that when the lattice size of simulation increased the crystal structure becomes more like quasi crystal at the low temperature.

  17. Spatially anisotropic Heisenberg kagome antiferromagnet

    Science.gov (United States)

    Apel, W.; Yavors'kii, T.; Everts, H.-U.

    2007-04-01

    In the search for spin-1/2 kagome antiferromagnets, the mineral volborthite has recently been the subject of experimental studies (Hiroi et al 2001 J. Phys. Soc. Japan 70 3377; Fukaya et al 2003 Phys. Rev. Lett. 91 207603; Bert et al 2004 J. Phys.: Condens. Matter 16 S829; Bert et al 2005 Phys. Rev. Lett. 95 087203). It has been suggested that the magnetic properties of this material are described by a spin-1/2 Heisenberg model on the kagome lattice with spatially anisotropic exchange couplings. We report on investigations of the {\\mathrm {Sp}}(\\mathcal {N}) symmetric generalization of this model in the large \\mathcal {N} limit. We obtain a detailed description of the dependence of possible ground states on the anisotropy and on the spin length S. A fairly rich phase diagram with a ferrimagnetic phase, incommensurate phases with and without long-range order and a decoupled chain phase emerges.

  18. Quenched bond randomness in marginal and non-marginal Ising spin models in 2D

    Science.gov (United States)

    Fytas, N. G.; Malakis, A.; Hadjiagapiou, I. A.

    2008-11-01

    We investigate and contrast, via entropic sampling based on the Wang-Landau algorithm, the effects of quenched bond randomness on the critical behavior of two Ising spin models in 2D. The random bond version of the superantiferromagnetic (SAF) square model with nearest- and next-nearest-neighbor competing interactions and the corresponding version of the simple Ising model are studied, and their general universality aspects are inspected by means of a detailed finite size scaling (FSS) analysis. We find that the random bond SAF model obeys weak universality, hyperscaling, and exhibits a strong saturating behavior of the specific heat due to the competing nature of interactions. On the other hand, for the random Ising model we encounter some difficulties as regards a definite discrimination between the two well-known scenarios of the logarithmic corrections versus the weak universality. However, a careful FSS analysis of our data favors the field theoretically predicted logarithmic corrections.

  19. The scaling limit of the energy correlations in non integrable Ising models

    CERN Document Server

    Giuliani, Alessandro; Mastropietro, Vieri

    2012-01-01

    We obtain an explicit expression for the multipoint energy correlations of a non solvable two-dimensional Ising models with nearest neighbor ferromagnetic interactions plus a weak finite range interaction of strength $\\lambda$, in a scaling limit in which we send the lattice spacing to zero and the temperature to the critical one. Our analysis is based on an exact mapping of the model into an interacting lattice fermionic theory, which generalizes the one originally used by Schultz, Mattis and Lieb for the nearest neighbor Ising model. The interacting model is then analyzed by a multiscale method first proposed by Pinson and Spencer. If the lattice spacing is finite, then the correlations cannot be computed in closed form: rather, they are expressed in terms of infinite, convergent, power series in $\\lambda$. In the scaling limit, these infinite expansions radically simplify and reduce to the limiting energy correlations of the integrable Ising model, up to a finite renormalization of the parameters. Explicit...

  20. The quantum Ising model: finite sums and hyperbolic functions

    Science.gov (United States)

    Damski, Bogdan

    2015-10-01

    We derive exact closed-form expressions for several sums leading to hyperbolic functions and discuss their applicability for studies of finite-size Ising spin chains. We show how they immediately lead to closed-form expressions for both fidelity susceptibility characterizing the quantum critical point and the coefficients of the counterdiabatic Hamiltonian enabling arbitrarily quick adiabatic driving of the system. Our results generalize and extend the sums presented in the popular Gradshteyn and Ryzhik Table of Integrals, Series, and Products.

  1. The quantum Ising model: finite sums and hyperbolic functions

    OpenAIRE

    Bogdan Damski

    2015-01-01

    We derive exact closed-form expressions for several sums leading to hyperbolic functions and discuss their applicability for studies of finite-size Ising spin chains. We show how they immediately lead to closed-form expressions for both fidelity susceptibility characterizing the quantum critical point and the coefficients of the counterdiabatic Hamiltonian enabling arbitrarily quick adiabatic driving of the system. Our results generalize and extend the sums presented in the popular Gradshteyn...

  2. Static and dynamical spin correlations of the S =1/2 random-bond antiferromagnetic Heisenberg model on the triangular and kagome lattices

    Science.gov (United States)

    Shimokawa, Tokuro; Watanabe, Ken; Kawamura, Hikaru

    2015-10-01

    Inspired by the recent theoretical suggestion that the random-bond S =1 /2 antiferromagnetic Heisenberg model on the triangular and the kagome lattices might exhibit a randomness-induced quantum spin liquid (QSL) behavior when the strength of the randomness exceeds a critical value, and that this "random-singlet state" might be relevant to the QSL behaviors experimentally observed in triangular organic salts κ -(ET) 2Cu2(CN) 3 and EtMe3Sb [Pd(dmit)2] 2 and in kagome herbertsmithite ZnCu3(OH) 6Cl2 , we further investigate the nature of the static and the dynamical spin correlations of these models. We compute the static and the dynamical spin structure factors, S (q ) and S (q ,ω ) , by means of an exact diagonalization method. In both triangular and kagome models, the computed S (q ,ω ) in the random-singlet state depends on the wave vector q only weakly, robustly exhibiting gapless behaviors accompanied by the broad distribution extending to higher energy ω . Especially in the strongly random kagome model, S (q ,ω ) hardly depends on q , and exhibits an almost flat distribution for a wide range of ω , together with a ω =0 peak. These features agree semiquantitatively with the recent neutron-scattering data on a single-crystal herbertsmithite. Furthermore, the computed magnetization curve agrees almost quantitatively with the experimental one recently measured on a single-crystal herbertsmithite. These results suggest that the QSL state observed in herbertsmithite might indeed be the randomness-induced QSL state, i.e., the random-singlet state.

  3. Exact solutions to plaquette Ising models with free and periodic boundaries

    Directory of Open Access Journals (Sweden)

    Marco Mueller

    2017-01-01

    We clarify the exact relation between partition functions with free and periodic boundary conditions expressed in terms of original and product spin variables for the 2d plaquette and 3d fuki-nuke models, noting that the differences are already present in the 1d Ising model. In addition, we solve the 2d plaquette Ising model with helical boundary conditions. The various exactly solved examples illustrate how correlations can be induced in finite systems as a consequence of the choice of boundary conditions.

  4. Multipartite Entanglement in a One-Dimensional Time Dependent Ising Model

    CERN Document Server

    Lakshminarayan, A; Lakshminarayan, Arul

    2004-01-01

    We study multipartite entanglement measures for a one-dimensional Ising chain that is capable of showing both integrable and nonintegrable behaviour. This model includes the kicked transverse Ising model, which we solve exactly using the Jordan-Wigner transform, as well as nonintegrable and mixing regimes. The cluster states arise as a special case and we show that while one measure of entanglement is large, another measure can be exponentially small, while symmetrizing these states with respect to up and down spins, produces those with large entanglement content uniformly. We also calculate exactly some entanglement measures for the nontrivial but integrable case of the kicked transverse Ising model. In the nonintegrable case we begin on extensive numerical studies that shows that large multipartite entanglement is accompanied by diminishing two-body correlations, and that time averaged multipartite entanglement measures can be enhanced in nonintegrable systems.

  5. GPU-based single-cluster algorithm for the simulation of the Ising model

    Science.gov (United States)

    Komura, Yukihiro; Okabe, Yutaka

    2012-02-01

    We present the GPU calculation with the common unified device architecture (CUDA) for the Wolff single-cluster algorithm of the Ising model. Proposing an algorithm for a quasi-block synchronization, we realize the Wolff single-cluster Monte Carlo simulation with CUDA. We perform parallel computations for the newly added spins in the growing cluster. As a result, the GPU calculation speed for the two-dimensional Ising model at the critical temperature with the linear size L = 4096 is 5.60 times as fast as the calculation speed on a current CPU core. For the three-dimensional Ising model with the linear size L = 256, the GPU calculation speed is 7.90 times as fast as the CPU calculation speed. The idea of quasi-block synchronization can be used not only in the cluster algorithm but also in many fields where the synchronization of all threads is required.

  6. GPU-based single-cluster algorithm for the simulation of the Ising model

    CERN Document Server

    Komura, Yukihiro

    2011-01-01

    We present the GPU calculation with the common unified device architecture (CUDA) for the Wolff single-cluster algorithm of the Ising model. Proposing an algorithm for a quasi-block synchronization, we realize the Wolff single-cluster Monte Carlo simulation with CUDA. We perform parallel computations for the newly added spins in the growing cluster. As a result, the GPU calculation speed for the two-dimensional Ising model at the critical temperature with the linear size L=4096 is 5.60 times as fast as the calculation speed on a current CPU core. For the three-dimensional Ising model with the linear size L=256, the GPU calculation speed is 7.90 times as fast as the CPU calculation speed. The idea of quasi-block synchronization can be used not only in the cluster algorithm but also in many fields where the synchronization of all threads is required.

  7. Mathematical structure of the three-dimensional (3D) Ising model

    Institute of Scientific and Technical Information of China (English)

    Zhang Zhi-Dong

    2013-01-01

    An overview of the mathematical structure of the three-dimensional (3D) Ising model is given from the points of view of topology,algebra,and geometry.By analyzing the relationships among transfer matrices of the 3D Ising model,Reidemeister moves in the knot theory,Yang-Baxter and tetrahedron equations,the following facts are illustrated for the 3D Ising model.1) The complex quaternion basis constructed for the 3D Ising model naturally represents the rotation in a (3+1)-dimensional space-time as a relativistic quantum statistical mechanics model,which is consistent with the 4-fold integrand of the partition function obtained by taking the time average.2) A unitary transformation with a matrix that is a spin representation in 2n·l·o-space corresponds to a rotation in 2n· l· o-space,which serves to smooth all the crossings in the transfer matrices and contributes the non-trivial topological part of the partition function of the 3D Ising model.3)A tetrahedron relationship would ensure the commutativity of the transfer matrices and the integrability of the 3D Ising model,and its existence is guaranteed by the Jordan algebra and the Jordan-von Neumann-Wigner procedures.4) The unitary transformation for smoothing the crossings in the transfer matrices changes the wave functions by complex phases Φx,Φy,and Φz.The relationship with quantum field and gauge theories and the physical significance of the weight factors are discussed in detail.The conjectured exact solution is compared with numerical results,and the singularities at/near infinite temperature are inspected.The analyticity in β =1/(kBT) of both the hard-core and the Ising models has been proved only forβ > 0,not for β =0.Thus the high-temperature series cannot serve as a standard for judging a putative exact solution of the 3D Ising model.

  8. Physics and financial economics (1776-2014): puzzles, Ising and agent-based models.

    Science.gov (United States)

    Sornette, Didier

    2014-06-01

    This short review presents a selected history of the mutual fertilization between physics and economics--from Isaac Newton and Adam Smith to the present. The fundamentally different perspectives embraced in theories developed in financial economics compared with physics are dissected with the examples of the volatility smile and of the excess volatility puzzle. The role of the Ising model of phase transitions to model social and financial systems is reviewed, with the concepts of random utilities and the logit model as the analog of the Boltzmann factor in statistical physics. Recent extensions in terms of quantum decision theory are also covered. A wealth of models are discussed briefly that build on the Ising model and generalize it to account for the many stylized facts of financial markets. A summary of the relevance of the Ising model and its extensions is provided to account for financial bubbles and crashes. The review would be incomplete if it did not cover the dynamical field of agent-based models (ABMs), also known as computational economic models, of which the Ising-type models are just special ABM implementations. We formulate the 'Emerging Intelligence Market Hypothesis' to reconcile the pervasive presence of 'noise traders' with the near efficiency of financial markets. Finally, we note that evolutionary biology, more than physics, is now playing a growing role to inspire models of financial markets.

  9. Physics and financial economics (1776-2014): puzzles, Ising and agent-based models

    Science.gov (United States)

    Sornette, Didier

    2014-06-01

    This short review presents a selected history of the mutual fertilization between physics and economics—from Isaac Newton and Adam Smith to the present. The fundamentally different perspectives embraced in theories developed in financial economics compared with physics are dissected with the examples of the volatility smile and of the excess volatility puzzle. The role of the Ising model of phase transitions to model social and financial systems is reviewed, with the concepts of random utilities and the logit model as the analog of the Boltzmann factor in statistical physics. Recent extensions in terms of quantum decision theory are also covered. A wealth of models are discussed briefly that build on the Ising model and generalize it to account for the many stylized facts of financial markets. A summary of the relevance of the Ising model and its extensions is provided to account for financial bubbles and crashes. The review would be incomplete if it did not cover the dynamical field of agent-based models (ABMs), also known as computational economic models, of which the Ising-type models are just special ABM implementations. We formulate the ‘Emerging Intelligence Market Hypothesis’ to reconcile the pervasive presence of ‘noise traders’ with the near efficiency of financial markets. Finally, we note that evolutionary biology, more than physics, is now playing a growing role to inspire models of financial markets.

  10. Self-Organizing Two-Temperature Ising Model Describing Human Segregation

    Science.gov (United States)

    Ódor, Géza

    A two-temperature Ising-Schelling model is introduced and studied for describing human segregation. The self-organized Ising model with Glauber kinetics simulated by Müller et al. exhibits a phase transition between segregated and mixed phases mimicking the change of tolerance (local temperature) of individuals. The effect of external noise is considered here as a second temperature added to the decision of individuals who consider a change of accommodation. A numerical evidence is presented for a discontinuous phase transition of the magnetization.

  11. Gauge model with Ising vacancies: Multicritical behavior of self-avoiding surfaces

    Science.gov (United States)

    Maritan, A.; Seno, F.; Stella, A. L.

    1991-08-01

    A openZ2 gauge model with n-component-vector degrees of freedom on a dodecahedral lattice is coupled to an Ising system on the dual lattice. The statistics of interacting self-avoiding surfaces (SAS) is obtained in the n-->0 limit. At the percolative critical point an exact identification of the SAS critical behavior with that of Ising cluster hulls holds. This condition corresponds to a multicritical point for SAS, in universality class different from that of branched polymers. The model allows application of standard statistical methods to SAS. A mean-field calculation gives a phase diagram remarkably consistent with the above results.

  12. Empirical relations between static and dynamic exponents for Ising model cluster algorithms

    Science.gov (United States)

    Coddington, Paul D.; Baillie, Clive F.

    1992-02-01

    We have measured the autocorrelations for the Swendsen-Wang and the Wolff cluster update algorithms for the Ising model in two, three, and four dimensions. The data for the Wolff algorithm suggest that the autocorrelations are linearly related to the specific heat, in which case the dynamic critical exponent is zint,EW=α/ν. For the Swendsen-Wang algorithm, scaling the autocorrelations by the average maximum cluster size gives either a constant or a logarithm, which implies that zint,ESW=β/ν for the Ising model.

  13. Empirical relations between static and dynamic exponents for Ising model cluster algorithms

    Energy Technology Data Exchange (ETDEWEB)

    Coddington, P.D. (Department of Physics, Syracuse University, Syracuse, New York 13244 (United States)); Baillie, C.F. (Department of Physics, University of Colorado, Boulder, Colorado 80309 (United States))

    1992-02-17

    We have measured the autocorrelations for the Swendsen-Wang and the Wolff cluster update algorithms for the Ising model in two, three, and four dimensions. The data for the Wolff algorithm suggest that the autocorrelations are linearly related to the specific heat, in which case the dynamic critical exponent is {ital z}{sub int,}{ital E}{sup W}={alpha}/{nu}. For the Swendsen-Wang algorithm, scaling the autocorrelations by the average maximum cluster size gives either a constant or a logarithm, which implies that {ital z}{sub int,}{ital E}{sup SW}={beta}/{nu} for the Ising model.

  14. Overlap distribution of the three-dimensional Ising model.

    Science.gov (United States)

    Berg, Bernd A; Billoire, Alain; Janke, Wolfhard

    2002-10-01

    We study the Parisi overlap probability density P(L)(q) for the three-dimensional Ising ferromagnet by means of Monte Carlo (MC) simulations. At the critical point, P(L)(q) is peaked around q=0 in contrast with the double peaked magnetic probability density. We give particular attention to the tails of the overlap distribution at the critical point, which we control over up to 500 orders of magnitude by using the multioverlap MC algorithm. Below the critical temperature, interface tension estimates from the overlap probability density are given and their approach to the infinite volume limit appears to be smoother than for estimates from the magnetization.

  15. Boundary States and Correlation Functions of Tricritical Ising Model from Coulomb-Gas Formalism

    Institute of Scientific and Technical Information of China (English)

    Smain Balaska; Toufik Sahabi

    2009-01-01

    We consider the minimal conformal model describing the tricritical Ising model on the disk and on the upper half plane. Using the coulomb-gas formalism we determine its consistents boundary states as well as its one-point and two-point correlation functions.

  16. Exact solutions to plaquette Ising models with free and periodic boundaries

    Science.gov (United States)

    Mueller, Marco; Johnston, Desmond A.; Janke, Wolfhard

    2017-01-01

    An anisotropic limit of the 3d plaquette Ising model, in which the plaquette couplings in one direction were set to zero, was solved for free boundary conditions by Suzuki (1972) [1], who later dubbed it the fuki-nuke, or "no-ceiling", model. Defining new spin variables as the product of nearest-neighbour spins transforms the Hamiltonian into that of a stack of (standard) 2d Ising models and reveals the planar nature of the magnetic order, which is also present in the fully isotropic 3d plaquette model. More recently, the solution of the fuki-nuke model was discussed for periodic boundary conditions, which require a different approach to defining the product spin transformation, by Castelnovo et al. (2010) [2]. We clarify the exact relation between partition functions with free and periodic boundary conditions expressed in terms of original and product spin variables for the 2d plaquette and 3d fuki-nuke models, noting that the differences are already present in the 1d Ising model. In addition, we solve the 2d plaquette Ising model with helical boundary conditions. The various exactly solved examples illustrate how correlations can be induced in finite systems as a consequence of the choice of boundary conditions.

  17. Universality of the Ising and the S=1 model on Archimedean lattices: A Monte Carlo determination

    Science.gov (United States)

    Malakis, A.; Gulpinar, G.; Karaaslan, Y.; Papakonstantinou, T.; Aslan, G.

    2012-03-01

    The Ising models S=1/2 and S=1 are studied by efficient Monte Carlo schemes on the (3,4,6,4) and the (3,3,3,3,6) Archimedean lattices. The algorithms used, a hybrid Metropolis-Wolff algorithm and a parallel tempering protocol, are briefly described and compared with the simple Metropolis algorithm. Accurate Monte Carlo data are produced at the exact critical temperatures of the Ising model for these lattices. Their finite-size analysis provide, with high accuracy, all critical exponents which, as expected, are the same with the well-known 2D Ising model exact values. A detailed finite-size scaling analysis of our Monte Carlo data for the S=1 model on the same lattices provides very clear evidence that this model obeys, also very well, the 2D Ising model critical exponents. As a result, we find that recent Monte Carlo simulations and attempts to define effective dimensionality for the S=1 model on these lattices are misleading. Accurate estimates are obtained for the critical amplitudes of the logarithmic expansions of the specific heat for both models on the two Archimedean lattices.

  18. Sublattice magnetizations in non-zero magnetic field in an antiferromagnetic infinite-range Ising model

    Energy Technology Data Exchange (ETDEWEB)

    Ayuela, A. [Donostia International Physics Center (DIPC), P.O. Box 1072, 20018 San Sebastian/Donostia (Spain)]. E-mail: swxayfea@sw.ehu.es; Klein, D.J. [Department of Marine Science, Texas A and M University at Galveston, Galveston, TX 77553 (United States); March, N.H. [Donostia International Physics Center (DIPC), P.O. Box 1072, 20018 San Sebastian/Donostia (Spain) and Oxford University, Oxford (United Kingdom)]. E-mail: arubio@sc.ehu.es

    2007-03-12

    The critical line of an Ising antiferromagnet (AF) with short-range exchange interactions has been discussed fairly recently by Wang and Kim. Their results may prove appropriate to some insulating AFs. Here, because of possible relevance to metallic AFs such as FeNiCr alloys, we study the Ising model in the opposite limit in which the exchange interactions become infinite range. In particular, we present numerical results for the sublattice magnetizations m{sub A} and m{sub B} as a function of the temperature and applied field. Then, using the so-called smoothness postulate, the critical line of an AF with infinite-range interactions is obtained.

  19. Information cascade, Kirman's ant colony model, and kinetic Ising model

    CERN Document Server

    Hisakado, Masato

    2014-01-01

    In this paper, we discuss a voting model in which voters can obtain information from a finite number of previous voters. There exist three groups of voters: (i) digital herders and independent voters, (ii) analog herders and independent voters, and (iii) tanh-type herders. In our previous paper, we used the mean field approximation for case (i). In that study, if the reference number r is above three, phase transition occurs and the solution converges to one of the equilibria. In contrast, in the current study, the solution oscillates between the two equilibria, that is, good and bad equilibria. In this paper, we show that there is no phase transition when r is finite. If the annealing schedule is adequately slow from finite r to infinite r, the voting rate converges only to the good equilibrium. In case (ii), the state of reference votes is equivalent to that of Kirman's ant colony model, and it follows beta binomial distribution. In case (iii), we show that the model is equivalent to the finite-size kinetic...

  20. q-Ising model on a duplex and a partially duplex clique

    CERN Document Server

    Chmiel, Anna; Sznajd-Weron, Katarzyna

    2016-01-01

    We analyze a modified kinetic Ising model, so called $q$- neighbor Ising model, with Metropolis dynamics,[Phys. Rev. E {\\bf92} 052105] on a duplex clique and a partially duplex clique. In the $q$-Ising model each spin interacts only with $q$ spins randomly chosen from the whole neighborhood. In the case of a duplex clique the change of a spin is allowed only if both levels simultaneously induce this change. Due to the mean-field like nature of the model we are able to derive the analytic form of transition probabilities and solve the corresponding master equation. The existence of the second level changes dramatically the character of the phase transition. In the case of the monoplex clique, the $q$-neighbor Ising model exhibits continuous phase transition for $q=3$, discontinuous phase transition for $q \\ge 4$ and for $q=1$ and $q=2$ the phase transition is not observed. On the other hand, in the case of the duplex clique continuous phase transitions are observed for all values of $q$, even for $q=1$ and $q=...

  1. Numerical evidence for a chiral spin liquid in the XXZ model on the kagome lattice in a magnetic field

    Science.gov (United States)

    Changlani, Hitesh; Kumar, Krishna; Clark, Bryan; Fradkin, Eduardo

    Frustrated spin systems in two dimensions provide a fertile ground for discovering exotic states of matter, often with topologically non-trivial properties. In this work, we investigate the possible existence of a chiral spin liquid state in the spin 1/2 XXZ model on the frustrated kagome lattice in the presence of a magnetic field. This model is equivalent to a hard-core bosonic one with density-density interactions at finite filling fraction. Motivated by previous field theoretic predictions utilizing a Chern-Simons theory adapted for this lattice, we focus our attention to understanding the XY limit for the 2/3 magnetization plateau (equivalent to a system of hard-core bosons at 1/6 filling with weak nearest-neighbor repulsive interactions). Performing exact or accurate numerical computations, and based on energetics and construction of minimally entangled states and associated modular matrices, we provide evidence for such a spin liquid. We study the nature of this phase and examine its stability to additional interactions. We acknowledge support from the SciDAC program under Award Number DE-FG02-12ER46875.

  2. Modeling of the financial market using the two-dimensional anisotropic Ising model

    Science.gov (United States)

    Lima, L. S.

    2017-09-01

    We have used the two-dimensional classical anisotropic Ising model in an external field and with an ion single anisotropy term as a mathematical model for the price dynamics of the financial market. The model presented allows us to test within the same framework the comparative explanatory power of rational agents versus irrational agents with respect to the facts of financial markets. We have obtained the mean price in terms of the strong of the site anisotropy term Δ which reinforces the sensitivity of the agent's sentiment to external news.

  3. Bootstrapping Mixed Correlators in the 3D Ising Model

    CERN Document Server

    Kos, Filip; Simmons-Duffin, David

    2014-01-01

    We study the conformal bootstrap for systems of correlators involving non-identical operators. The constraints of crossing symmetry and unitarity for such mixed correlators can be phrased in the language of semidefinite programming. We apply this formalism to the simplest system of mixed correlators in 3D CFTs with a $\\mathbb{Z}_2$ global symmetry. For the leading $\\mathbb{Z}_2$-odd operator $\\sigma$ and $\\mathbb{Z}_2$-even operator $\\epsilon$, we obtain numerical constraints on the allowed dimensions $(\\Delta_\\sigma, \\Delta_\\epsilon)$ assuming that $\\sigma$ and $\\epsilon$ are the only relevant scalars in the theory. These constraints yield a small closed region in $(\\Delta_\\sigma, \\Delta_\\epsilon)$ space compatible with the known values in the 3D Ising CFT.

  4. Interfaces in driven Ising models: shear enhances confinement.

    Science.gov (United States)

    Smith, Thomas H R; Vasilyev, Oleg; Abraham, Douglas B; Maciołek, Anna; Schmidt, Matthias

    2008-08-08

    We use a phase-separated driven two-dimensional Ising lattice gas to study fluid interfaces exposed to shear flow parallel to the interface. The interface is stabilized by two parallel walls with opposing surface fields, and a driving field parallel to the walls is applied which (i) either acts locally at the walls or (ii) varies linearly with distance across the strip. Using computer simulations with Kawasaki dynamics, we find that the system reaches a steady state in which the magnetization profile is the same as that in equilibrium, but with a rescaled length implying a reduction of the interfacial width. An analogous effect was recently observed in sheared phase-separated colloidal dispersions. Pair correlation functions along the interface decay more rapidly with distance under drive than in equilibrium and for cases of weak drive, can be rescaled to the equilibrium result.

  5. Small-world phenomena in physics: the Ising model

    Energy Technology Data Exchange (ETDEWEB)

    Gitterman, M. [Department of Physics, Bar-Ilan University, Ramat-Gan (Israel)

    2000-12-01

    The Ising system with a small fraction of random long-range interactions is the simplest example of small-world phenomena in physics. Considering the latter both in an annealed and in a quenched state we conclude that: (a) the existence of random long-range interactions leads to a phase transition in the one-dimensional case and (b) there is a minimal average number p of these interactions per site (p<1 in the annealed state, and p{approx_equal}1 in the quenched state) needed for the appearance of the phase transition. Note that the average number of these bonds, pN/2, is much smaller than the total number of bonds, N{sup 2}/2. (author)

  6. Effect of Bond-Diluted on Spin-3/2 Transverse Ising Model with Crystal Field

    Institute of Scientific and Technical Information of China (English)

    JIANG Wei; LU Zhan-Hong; WEI Guo-Zhu; DU An

    2002-01-01

    The magnetic properties of the bond-diluted spin-3/2 transverse Ising model with the presence of a crystalfield on the honeycomb lattice are studied within the framework of the effective field theory with correlations. Theinteractions Jij are assumed to be independent random variables with distribution P(Jij) = pδ(Jij - J) + (1 - P)δ(Jij).

  7. CRITICAL BEHAVIOR OF S-3/2 ISING MODEL IN RANDOM LONGITUDINAL AND TRANSVERSE FIELDS

    Institute of Scientific and Technical Information of China (English)

    宋为基

    1995-01-01

    The phase diagrams and the other crtical properties of S-3/2 Ising model in random longitudinal and transverse fields(RLIM) are dicussed with the approximate scheme combined by mean-field renormalization group theory(MFRG) and the discretized path-integral representation(DPIR).

  8. Lifshitz-Allen-Cahn domain-growth kinetics of Ising models with conserved density

    DEFF Research Database (Denmark)

    Fogedby, Hans C.; Mouritsen, Ole G.

    1988-01-01

    The domain-growth kinetics of p=fourfold degenerate (2×1) ordering in two-dimensional Ising models with conserved density is studied as a function of temperature and range of Kawasaki spin exchange. It is found by computer simulations that the zero-temperature freezing-in behavior for nearest...

  9. On the diagonal susceptibility of the two-dimensional Ising model

    Energy Technology Data Exchange (ETDEWEB)

    Tracy, Craig A. [Department of Mathematics, University of California, Davis, California 95616 (United States); Widom, Harold [Department of Mathematics, University of California, Santa Cruz, California 95064 (United States)

    2013-12-15

    We consider the diagonal susceptibility of the isotropic 2D Ising model for temperatures below the critical temperature. For a parameter k related to temperature and the interaction constant, we extend the diagonal susceptibility to complex k inside the unit disc, and prove the conjecture that the unit circle is a natural boundary.

  10. Multiple Ising models coupled to 2-d gravity: a CSD analysis

    Science.gov (United States)

    Bowick, Mark; Falcioni, Marco; Harris, Geoffrey; Marinari, Enzo

    1994-04-01

    We simulate single and multiple Ising models coupled to 2-d gravity and we measure critical slowing down (CSD) with the standard methods. We find that the Swendsen-Wang and Wolff cluster algorithms do not eliminate CSD. We interpret the result as an effect of the mesh dynamics.

  11. Critical Dynamics Behavior of the Wolff Algorithm in the Site-Bond-Correlated Ising Model

    Science.gov (United States)

    Campos, P. R. A.; Onody, R. N.

    Here we apply the Wolff single-cluster algorithm to the site-bond-correlated Ising model and study its critical dynamical behavior. We have verified that the autocorrelation time diminishes in the presence of dilution and correlation, showing that the Wolff algorithm performs even better in such situations. The critical dynamical exponents are also estimated.

  12. Energy fluctuations and the singularity of specific heat in a 3D Ising model

    Science.gov (United States)

    Kaupuzs, Jevgenijs

    2004-05-01

    We study the energy fluctuations in 3D Ising model near the phase transition point. Specific heat is a relevant quantity which is directly related to the mean squared amplitude of the energy fluctuations in the system. We have made extensive Monte Carlo simulations in 3D Ising model to clarify the character of the singularity of the specific heat Cv based on the finite-size scaling of its maximal values Cvmax depending on the linear size of the lattice L. An original iterative method has been used which automatically finds the pseudocritical temperature corresponding to the maximum of Cv. The simulations made up to L Wolff's cluster algorithm allowed us to verify the possible power-like as well as logarithmic singularity of the specific heat predicted by different theoretical treatments. The most challenging and interesting result we have obtained is that the finite-size scaling of Cvmax in 3D Ising model is well described by a logarithmic rather than power-like ansatz, just like in 2D case. Another modification of our iterative method has been considered to estimate the critical coupling of 3D Ising model from the Binder cumulant data within L ɛ [96; 384]. Furthermore, the critical exponent β has been evaluated from the simulated magnetization data within the range of reduced temperatures t >= 0.000086 and system sizes L <= 410.

  13. Red-bond exponents of the critical and the tricritical Ising model in three dimensions

    Science.gov (United States)

    Deng, Youjin; Blöte, Henk W. J.

    2004-11-01

    Using the Wolff and geometric cluster algorithms and finite-size scaling analysis, we investigate the critical Ising and the tricritical Blume-Capel models with nearest-neighbor interactions on the simple-cubic lattice. The sampling procedure involves the decomposition of the Ising configuration into geometric clusters, each of which consists of a set of nearest-neighboring spins of the same sign connected with bond probability p . These clusters include the well-known Kasteleyn-Fortuin clusters as a special case for p=1-exp(-2K) , where K is the Ising spin-spin coupling. Along the critical line K=Kc , the size distribution of geometric clusters is investigated as a function of p . We observe that, unlike in the case of two-dimensional tricriticality, the percolation threshold in both models lies at pc=1-exp(-2Kc) . Further, we determine the corresponding red-bond exponents as yr=0.757(2) and 0.501(5) for the critical Ising and the tricritical Blume-Capel models, respectively. On this basis, we conjecture yr=1/2 for the latter model.

  14. Finite-size scaling of interface free energies in the 3d Ising model

    CERN Document Server

    Pepé, M; Forcrand, Ph. de

    2002-01-01

    We perform a study of the universality of the finite size scaling functions of interface free energies in the 3d Ising model. Close to the hot/cold phase transition, we observe very good agreement with the same scaling functions of the 4d SU(2) Yang--Mills theory at the deconfinement phase transition.

  15. A Manifold of Pure Gibbs States of the Ising Model on the Lobachevsky Plane

    Science.gov (United States)

    Gandolfo, Daniel; Ruiz, Jean; Shlosman, Senya

    2015-02-01

    In this paper we construct many `new' Gibbs states of the Ising model on the Lobachevsky plane, the millefeuilles. Unlike the usual states on the integer lattices, our foliated states have infinitely many interfaces. The interfaces are rigid and fill the Lobachevsky plane with positive density. We also construct analogous states on the Cayley trees.

  16. Finite-size scaling of interface free energies in the 3d Ising model

    OpenAIRE

    Pepe, M.; de Forcrand, Ph.

    2001-01-01

    We perform a study of the universality of the finite size scaling functions of interface free energies in the 3d Ising model. Close to the hot/cold phase transition, we observe very good agreement with the same scaling functions of the 4d SU(2) Yang--Mills theory at the deconfinement phase transition.

  17. Condensation of handles in the interface of 3D Ising model

    OpenAIRE

    Caselle, M.; Gliozzi, F.; Vinti, S.

    1993-01-01

    We analyze the microscopic, topological structure of the interface between domains of opposite magnetization in 3D Ising model near the critical point. This interface exhibits a fractal behaviour with a high density of handles. The mean area is an almost linear function of the genus. The entropy exponent is affected by strong finite-size effects.

  18. Nonequilibrium critical dynamics of two dimensional interacting monomer-dimer model: non-Ising criticality

    Science.gov (United States)

    Nam, Keekwon; Kim, Bongsoo; Jong Lee, Sung

    2014-08-01

    We investigate the nonequilibrium relaxation dynamics of an interacting monomer-dimer model with nearest neighbor repulsion on a square lattice, which possesses two symmetric absorbing states. The model is known to exhibit two nearby continuous transitions: the Z2 symmetry-breaking order-disorder transition and the absorbing transition with directed percolation criticality. We performed a more detailed analysis of our extensive simulations on bigger lattice systems which reaffirms that the symmetry-breaking transition exhibits a non-Ising critical behavior with β ≃ 0.149(2) and η ≃ 0.30(1) that are distinct from those values of a pure two dimensional Ising model. Finite size scaling of dimer density near the symmetry breaking transition gives logarithmic scaling (α = 0.0) which is consistent with the hyperscaling relation but the corresponding exponent of νB ≃ 1.37(2) exhibits a conspicuous deviation from the pure Ising value of 1. The value of dynamic critical exponent z, however, is found to be close to that of the kinetic Ising model as 1/z ≃ 0.466(5) from the relaxation of staggered magnetization (and also similar but slightly smaller values from coarsening).

  19. Finite size scaling analysis of intermittency moments in the two dimensional Ising model

    CERN Document Server

    Burda, Z; Peschanski, R; Wosiek, J

    1993-01-01

    Finite size scaling is shown to work very well for the block variables used in intermittency studies on a 2-d Ising lattice. The intermittency exponents so derived exhibit the expected relations to the magnetic critical exponent of the model. Email contact: pesch@amoco.saclay.cea.fr

  20. Surprising convergence of the Monte Carlo renormalization group for the three-dimensional Ising model.

    Science.gov (United States)

    Ron, Dorit; Brandt, Achi; Swendsen, Robert H

    2017-05-01

    We present a surprisingly simple approach to high-accuracy calculations of the critical properties of the three-dimensional Ising model. The method uses a modified block-spin transformation with a tunable parameter to improve convergence in the Monte Carlo renormalization group. The block-spin parameter must be tuned differently for different exponents to produce optimal convergence.

  1. Numerical determination of the CFT central charge in the site-diluted Ising model

    CERN Document Server

    Belov, P A; Sorokin, A O

    2016-01-01

    We propose a new numerical method to determine the central charge of the conformal field theory models corresponding to the 2D lattice models. In this method, the free energy of the lattice model on the torus is calculated by the Wang-Landau algorithm and then the central charge is obtained from a free energy scaling with respect to the torus radii. The method is applied for determination of the central charge in the site-diluted Ising model.

  2. Solution of the antiferromagnetic Ising model on a tetrahedron recursive lattice.

    Science.gov (United States)

    Jurčišinová, E; Jurčišin, M

    2014-03-01

    We consider the antiferromagnetic spin-1/2 Ising model on the recursive tetrahedron lattice on which two elementary tetrahedrons are connected at each site. The model represents the simplest approximation of the antiferromagnetic Ising model on the real three-dimensional tetrahedron lattice which takes into account effects of frustration. An exact analytical solution of the model is found and discussed. It is shown that the model exhibits neither the first-order nor the second-order phase transitions. A detailed analysis of the magnetization of the model in the presence of the external magnetic field is performed and the existence of the magnetization plateaus for low temperatures is shown. All possible ground states of the model are found and discussed. The existence of nontrivial singular ground states is proven and exact explicit expressions for them are found.

  3. A model project for reproducible papers: critical temperature for the Ising model on a square lattice

    CERN Document Server

    Dolfi, M; Hehn, A; Imriška, J; Pakrouski, K; Rønnow, T F; Troyer, M; Zintchenko, I; Chirigati, F; Freire, J; Shasha, D

    2014-01-01

    In this paper we present a simple, yet typical simulation in statistical physics, consisting of large scale Monte Carlo simulations followed by an involved statistical analysis of the results. The purpose is to provide an example publication to explore tools for writing reproducible papers. The simulation estimates the critical temperature where the Ising model on the square lattice becomes magnetic to be Tc /J = 2.26934(6) using a finite size scaling analysis of the crossing points of Binder cumulants. We provide a virtual machine which can be used to reproduce all figures and results.

  4. Generalized hard-core dimer model approach to low-energy Heisenberg frustrated antiferromagnets: General properties and application to the kagome antiferromagnet

    Science.gov (United States)

    Schwandt, David; Mambrini, Matthieu; Poilblanc, Didier

    2010-06-01

    We propose a general nonperturbative scheme that quantitatively maps the low-energy sector of spin-1/2 frustrated Heisenberg antiferromagnets to effective generalized quantum dimer models. We develop the formal lattice-independent frame and establish some important results on (i) the locality of the generated Hamiltonians, (ii) how full resummations can be performed in this renormalization scheme. The method is then applied to the much debated kagome antiferromagnet for which a fully resummed effective Hamiltonian—shown to capture the essential properties and provide deep insights on the microscopic model [D. Poilblanc, M. Mambrini, and D. Schwandt, Phys. Rev. B 81, 180402(R) (2010)]—is derived.

  5. Ferromagnetic resonance and resonance modes in kagome lattices: From an open to a closed kagome structure

    Science.gov (United States)

    Dubowik, J.; Kuświk, P.; Matczak, M.; Bednarski, W.; Stobiecki, F.; Aleshkevych, P.; Szymczak, H.; Kisielewski, M.; Kisielewski, J.

    2016-06-01

    We present ferromagnetic resonance (FMR) investigations of 20 nm thick permalloy (Ni80Fe20 ) elements (width W =200 nm, length L =470 nm, period a =500 nm) arranged in open and closed artificial kagome lattices. The measurements were done at 9.4 and 34 GHz to ensure a saturated or near-saturated magnetic state of the kagome structures. The FMR data are analyzed in the framework of an analytical macrospin model which grasps the essential features of the bulk and edge modes at these microwave frequencies and is in agreement with the results of micromagnetic simulations. Polar plots of the resonance fields versus the field angle made by the direction of the magnetic field with respect to the main symmetry directions of the kagome lattice are compared with the results of the analytical model. The measured FMR spectra with a sixfold rotational symmetry qualitatively reproduce the structure expected from the theory. Magnetic dipolar interactions between the elements of the kagome lattices result in the mixing of edge and bulklike excitations at 9.4 GHz and in a systematic deviation from the model, especially for the closed kagome lattice.

  6. Dynamic Critical Exponents of Three-Dimensional Ising Models and Two-Dimensional Three-States Potts Models

    Science.gov (United States)

    Murase, Yohsuke; Ito, Nobuyasu

    2008-01-01

    Values of dynamic critical exponents are numerically estimated for various models with the nonequilibrium relaxation method to test the dynamic universality hypothesis. The dynamics used here are single-spin update with Metropolis-type transition probabities. The estimated values of nonequilibrium relaxation exponent of magnetization λm (=β/zν) of Ising models on bcc and fcc lattices are estimated to be 0.251(3) and 0.252(3), respectively, which are consistent with the value of the model on simple-cubic lattice, 0.250(2). The dynamic critical exponents of three-states Potts models on square, honeycomb and triangular lattices are also estimated to be 2.193(5), 2.198(4), and 2.199(3), respectively. They are consistent within the error bars. It is also confirmed that Ising models with regularly modulated coupling constants on square lattice have the same dynamic critical exponents with the uniformly ferromagnetic Ising model.

  7. An analysis of intergroup rivalry using Ising model and reinforcement learning

    Science.gov (United States)

    Zhao, Feng-Fei; Qin, Zheng; Shao, Zhuo

    2014-01-01

    Modeling of intergroup rivalry can help us better understand economic competitions, political elections and other similar activities. The result of intergroup rivalry depends on the co-evolution of individual behavior within one group and the impact from the rival group. In this paper, we model the rivalry behavior using Ising model. Different from other simulation studies using Ising model, the evolution rules of each individual in our model are not static, but have the ability to learn from historical experience using reinforcement learning technique, which makes the simulation more close to real human behavior. We studied the phase transition in intergroup rivalry and focused on the impact of the degree of social freedom, the personality of group members and the social experience of individuals. The results of computer simulation show that a society with a low degree of social freedom and highly educated, experienced individuals is more likely to be one-sided in intergroup rivalry.

  8. Ising and Gross-Neveu model in next-to-leading order

    CERN Document Server

    Knorr, Benjamin

    2016-01-01

    We study scalar and chiral fermionic models in next-to-leading order with the help of the functional renormalisation group. Their critical behaviour is of special interest in condensed matter systems, in particular graphene. To derive the beta functions, we make extensive use of computer algebra. The resulting flow equations were solved with pseudo-spectral methods to guarantee high accuracy. New estimates on critical quantities for both the Ising and the Gross-Neveu model are provided. For the Ising model, the estimates agree with earlier renormalisation group studies of the same level of approximation. By contrast, the approximation for the Gross-Neveu model retains many more operators than all earlier studies. For two Dirac fermions, the results agree with both lattice and large-$N_f$ calculations, but for a single flavour, different methods disagree quantitatively, and further studies are necessary.

  9. Observation of Schramm-Loewner evolution on the geometrical clusters of the Ising model

    Science.gov (United States)

    Najafi, M. N.

    2015-05-01

    Schramm-Loewner Evolution (SLE) is a stochastic process that, by focusing on the geometrical features of the two-dimensional (2D) conformal invariant models, classifies them using one real parameter κ. In this work we apply the SLE formalism to the exterior frontiers of the geometrical clusters (interfaces) of the two-dimensional critical Ising model on the triangular lattice. We first analyze the critical curves going from the real axis to the real axis in the upper half plane geometry and show numerically that SLE(κ, κ - 6) works well to extract the diffusivity parameter κ. We then analyze the conformal loops of the critical Ising model. After determining some geometrical exponents of the critical loops as the interfaces of the model in hand, we address the problem of application of SLE to conformal loops. We numerically show that SLE(κ, κ - 6) is more reliable than previous methods.

  10. Dannie Heineman Prize for Mathematical Physics Prize Lecture: Correlation Functions in Integrable Models: Ising Model and Monodromy Preserving Deformation

    Science.gov (United States)

    Miwa, Tetsuji

    2013-03-01

    Studies on integrable models in statistical mechanics and quantum field theory originated in the works of Bethe on the one-dimensional quantum spin chain and the work of Onsager on the two-dimensional Ising model. I will talk on the discovery in 1977 of the link between quantum field theory in the scaling limit of the two-dimensional Ising model and the theory of monodromy preserving linear ordinary differential equations. This work was the staring point of our journey with Michio Jimbo in integrable models, the journey which finally led us to the exact results on the correlation functions of quantum spin chains in 1992.

  11. Phase Transition of a Distance-Dependent Ising Model on the Barabasi-Albert Network

    Institute of Scientific and Technical Information of China (English)

    DAI Jun; HE Da-Ren

    2007-01-01

    We report our investigation on the behaviour of distance-dependent Ising models,which are located on the BA model network.The interaction strength between two nodes(the spins) is considered to obey an exponential decay dependence on the geometrical distance.The Monte Carlo simulation shows a phase transition from ferromagnetism to paramagnetism,and the critical temperature approaches a constant temperature as the interaction decaying exponent increases.

  12. Ground-state entanglement in a three-spin transverse Ising model with energy current

    Institute of Scientific and Technical Information of China (English)

    Zhang Yong; Liu Dan; Long Gui-Lu

    2007-01-01

    The ground-state entanglement associated with a three-spin transverse Ising model is studied. By introducing an energy current into the system, a quantum phase transition to energy-current phase may be presented with the variation of external magnetic field; and the ground-state entanglement varies suddenly at the critical point of quantum phase transition. In our model, the introduction of energy current makes the entanglement between any two qubits become maximally robust.

  13. The scaling limit of the energy correlations in non integrable Ising models

    OpenAIRE

    2012-01-01

    We obtain an explicit expression for the multipoint energy correlations of a non solvable two-dimensional Ising models with nearest neighbor ferromagnetic interactions plus a weak finite range interaction of strength $\\lambda$, in a scaling limit in which we send the lattice spacing to zero and the temperature to the critical one. Our analysis is based on an exact mapping of the model into an interacting lattice fermionic theory, which generalizes the one originally used by Schultz, Mattis an...

  14. Dynamics of the Random Ising Model with Long-Range Interaction

    Institute of Scientific and Technical Information of China (English)

    CHEN Yuan; LI Zhi-Bing; FANG Hai; HE Shun-Shan; SITU Shu-Ping

    2001-01-01

    Critical dynamics of the random Ising model with long-range interaction decaying as r-(d+σ) where d is the dimensionality) is studied by the theoretic renormalization-group approach. The system is released to an evolution within a model A dynamics. Asymptotic scaling laws are studied in a frame of the expansion in = 2σ - d. In dimensions d < 2σ. the dynamic exponent z is calculated to the second order in at the random fixed point.``

  15. Spin-1/2 Ising-Heisenberg model with the pair XYZ Heisenberg interaction and quartic Ising interactions as the exactly soluble zero-field eight-vertex model.

    Science.gov (United States)

    Strecka, Jozef; Canová, Lucia; Minami, Kazuhiko

    2009-05-01

    The spin-1/2 Ising-Heisenberg model with the pair XYZ Heisenberg interaction and quartic Ising interactions is exactly solved by establishing a precise mapping relationship with the corresponding zero-field (symmetric) eight-vertex model. It is shown that the Ising-Heisenberg model with the ferromagnetic Heisenberg interaction exhibits a striking critical behavior, which manifests itself through re-entrant phase transitions as well as continuously varying critical exponents. The changes in critical exponents are in accordance with the weak universality hypothesis in spite of a peculiar singular behavior that emerges at a quantum critical point of the infinite order, which occurs at the isotropic limit of the Heisenberg interaction. On the other hand, the Ising-Heisenberg model with the antiferromagnetic Heisenberg interaction surprisingly exhibits less significant changes in both critical temperatures and critical exponents upon varying the strength of the exchange anisotropy in the Heisenberg interaction.

  16. An Ising-Anderson model of localisation in high-temperature QCD

    CERN Document Server

    Giordano, Matteo; Pittler, Ferenc

    2015-01-01

    We discuss a possible mechanism leading to localisation of the low-lying Dirac eigenmodes in high-temperature lattice QCD, based on the spatial fluctuations of the local Polyakov lines in the partially ordered configurations above $T_c$. This mechanism provides a qualitative explanation of the dependence of localisation on the temperature and on the lattice spacing, and also of the phase diagram of QCD with an imaginary chemical potential. To test the viability of this mechanism we propose a three-dimensional effective, Anderson-like model, mimicking the effect of the Polyakov lines on the quarks. The diagonal, on-site disorder is governed by a three-dimensional Ising-like spin model with continuous spins. Our numerical results show that localised modes are indeed present in the ordered phase of the Ising model, thus supporting the proposed mechanism for localisation in QCD.

  17. Ising Model Spin S = 1 ON Directed BARABÁSI-ALBERT Networks

    Science.gov (United States)

    Lima, F. W. S.

    On directed Barabási-Albert networks with two and seven neighbours selected by each added site, the Ising model with spin S = 1/2 was seen not to show a spontaneous magnetisation. Instead, the decay time for flipping of the magnetisation followed an Arrhenius law for Metropolis and Glauber algorithms, but for Wolff cluster flipping the magnetisation decayed exponentially with time. On these networks the Ising model spin S = 1 is now studied through Monte Carlo simulations. However, in this model, the order-disorder phase transition is well defined in this system. We have obtained a first-order phase transition for values of connectivity m = 2 and m = 7 of the directed Barabási-Albert network.

  18. Self-similar transformations of lattice-Ising models at critical temperatures

    CERN Document Server

    Feng, You-gang

    2012-01-01

    We classify geometric blocks that serve as spin carriers into simple blocks and compound blocks by their topologic connectivity, define their fractal dimensions and describe the relevant transformations. By the hierarchical property of transformations and a block-spin scaling law we obtain a relation between the block spin and its carrier's fractal dimension. By mapping we set up a block-spin Gaussian model and get a formula connecting the critical point and the minimal fractal dimension of the carrier, which guarantees the uniqueness of a fixed point corresponding to the critical point, changing the complicated calculation of critical point into the simple one of the minimal fractal dimension. The numerical results of critical points with high accuracy for five conventional lattice-Ising models prove our method very effective and may be suitable to all lattice-Ising models. The origin of fluctuations in structure at critical temperature is discussed. Our method not only explains the problems met in the renor...

  19. Spin-1 Ising model: exact damage-spreading relations and numerical simulations.

    Science.gov (United States)

    Anjos, A S; Mariz, A M; Nobre, F D; Araujo, I G

    2008-09-01

    The nearest-neighbor-interaction spin-1 Ising model is investigated within the damage-spreading approach. Exact relations involving quantities computable through damage-spreading simulations and thermodynamic properties are derived for such a model, defined in terms of a very general Hamiltonian that covers several spin-1 models of interest in the literature. Such relations presuppose translational invariance and hold for any ergodic dynamical procedure, leading to an efficient tool for obtaining thermodynamic properties. The implementation of the method is illustrated through damage-spreading simulations for the ferromagnetic spin-1 Ising model on a square lattice. The two-spin correlation function and the magnetization are obtained, with precise estimates of their associated critical exponents and of the critical temperature of the model, in spite of the small lattice sizes considered. These results are in good agreement with the universality hypothesis, with critical exponents in the same universality class of the spin- 12 Ising model. The advantage of the present method is shown through a significant reduction of finite-size effects by comparing its results with those obtained from standard Monte Carlo simulations.

  20. Loops, Surfaces and Grassmann Representation in Two- and Three-Dimensional Ising Models

    CERN Document Server

    Gattringer, C R; Semenoff, Gordon W

    1999-01-01

    Starting from the known representation of the partition function of the 2- and 3-D Ising models as an integral over Grassmann variables, we perform a hopping expansion of the corresponding Pfaffian. We show that this expansion is an exact, algebraic representation of the loop- and surface expansions (with intrinsic geometry) of the 2- and 3-D Ising models. Such an algebraic calculus is much simpler to deal with than working with the geometrical objects. For the 2-D case we show that the algebra of hopping generators allows a simple algebraic treatment of the geometry factors and counting problems, and as a result we obtain the corrected loop expansion of the free energy. We compute the radius of convergence of this expansion and show that it is determined by the critical temperature. In 3-D the hopping expansion leads to the surface representation of the Ising model in terms of surfaces with intrinsic geometry. Based on a representation of the 3-D model as a product of 2-D models coupled to an auxiliary field...

  1. The scaling limit of the energy correlations in non-integrable Ising models

    Science.gov (United States)

    Giuliani, Alessandro; Greenblatt, Rafael L.; Mastropietro, Vieri

    2012-09-01

    We obtain an explicit expression for the multipoint energy correlations of a non-solvable two-dimensional Ising models with nearest neighbor ferromagnetic interactions plus a weak finite range interaction of strength λ, in a scaling limit in which we send the lattice spacing to zero and the temperature to the critical one. Our analysis is based on an exact mapping of the model into an interacting lattice fermionic theory, which generalizes the one originally used by Schultz, Mattis, and Lieb for the nearest neighbor Ising model. The interacting model is then analyzed by a multiscale method first proposed by Pinson and Spencer. If the lattice spacing is finite, then the correlations cannot be computed in closed form: rather, they are expressed in terms of infinite, convergent, power series in λ. In the scaling limit, these infinite expansions radically simplify and reduce to the limiting energy correlations of the integrable Ising model, up to a finite renormalization of the parameters. Explicit bounds on the speed of convergence to the scaling limit are derived.

  2. Application of Corner Transfer Matrix Renormalization Group Method to the Correlation Function of a Two-Dimensional Ising Model

    Institute of Scientific and Technical Information of China (English)

    何春山; 李志兵

    2003-01-01

    The correlation function of a two-dimensionalIsing model is calculated by the corner transfer matrix renormalization group method.We obtain the critical exponent η= 0.2496 with few computer resources.

  3. A Monte Carlo method for critical systems in infinite volume: the planar Ising model

    CERN Document Server

    Herdeiro, Victor

    2016-01-01

    In this paper we propose a Monte Carlo method for generating finite-domain marginals of critical distributions of statistical models in infinite volume. The algorithm corrects the problem of the long-range effects of boundaries associated to generating critical distributions on finite lattices. It uses the advantage of scale invariance combined with ideas of the renormalization group in order to construct a type of "holographic" boundary condition that encodes the presence of an infinite volume beyond it. We check the quality of the distribution obtained in the case of the planar Ising model by comparing various observables with their infinite-plane prediction. We accurately reproduce planar two-, three- and four-point functions of spin and energy operators. We also define a lattice stress-energy tensor, and numerically obtain the associated conformal Ward identities and the Ising central charge.

  4. Monte Carlo method for critical systems in infinite volume: The planar Ising model.

    Science.gov (United States)

    Herdeiro, Victor; Doyon, Benjamin

    2016-10-01

    In this paper we propose a Monte Carlo method for generating finite-domain marginals of critical distributions of statistical models in infinite volume. The algorithm corrects the problem of the long-range effects of boundaries associated to generating critical distributions on finite lattices. It uses the advantage of scale invariance combined with ideas of the renormalization group in order to construct a type of "holographic" boundary condition that encodes the presence of an infinite volume beyond it. We check the quality of the distribution obtained in the case of the planar Ising model by comparing various observables with their infinite-plane prediction. We accurately reproduce planar two-, three-, and four-point of spin and energy operators. We also define a lattice stress-energy tensor, and numerically obtain the associated conformal Ward identities and the Ising central charge.

  5. Rényi information flow in the Ising model with single-spin dynamics

    Science.gov (United States)

    Deng, Zehui; Wu, Jinshan; Guo, Wenan

    2014-12-01

    The n -index Rényi mutual information and transfer entropies for the two-dimensional kinetic Ising model with arbitrary single-spin dynamics in the thermodynamic limit are derived as functions of ensemble averages of observables and spin-flip probabilities. Cluster Monte Carlo algorithms with different dynamics from the single-spin dynamics are thus applicable to estimate the transfer entropies. By means of Monte Carlo simulations with the Wolff algorithm, we calculate the information flows in the Ising model with the Metropolis dynamics and the Glauber dynamics, respectively. We find that not only the global Rényi transfer entropy, but also the pairwise Rényi transfer entropy, peaks in the disorder phase.

  6. Hysteresis Loops and Phase Diagrams of the Spin-1 Ising Model in a Transverse Crystal Field

    Institute of Scientific and Technical Information of China (English)

    S. Bouhou; I. Essaoudi; A. Ainane; M. Saber; J. J. de Miguel; M. Kerouad1

    2012-01-01

    Within the framework of the effective-Geld theory with a probability distribution technique, which accounts for the self-spin correlation functions, the ferromagnetic spin-l Ising model with a transverse crystal field on honeycomb, square and simple cubic lattices is studied. We have investigated the effect of the transverse crystal field on the phase diagrams, magnetization, hysteresis loops and χz,h of the system. A number of interesting phenomena of the system are discussed.%Within the framework of the effective-field theory with a probability distribution technique,which accounts for the self-spin correlation functions,the ferromagnetic spin-1 Ising model with a transverse crystal field on honeycomb,square and simple cubic lattices is studied.We have investigated the effect of the transverse crystal field on the phase diagrams,magnetization,hysteresis loops and xz,h of the system.A number of interesting phenomena of the system are discussed.

  7. Critical Casimir forces between defects in the 2D Ising model

    Science.gov (United States)

    Nowakowski, P.; Maciołek, A.; Dietrich, S.

    2016-12-01

    An exact statistical mechanical derivation is given of the critical Casimir interactions between two defects in a planar lattice-gas Ising model. Each defect is a finite group of nearest-neighbor spins with modified coupling constants. Such a system can be regarded as a model of a binary liquid mixture with the molecules confined to a membrane and the defects mimicking protein inclusions embedded into the membrane. As suggested by recent experiments, certain cellular membranes appear to be tuned to the proximity of a critical demixing point belonging to the two-dimensional Ising universality class. Therefore one can expect the emergence of critical Casimir forces between membrane inclusions. These forces are governed by universal scaling functions, which we derive for simple defects. We prove that the scaling law appearing at criticality is the same for all types of defects considered here.

  8. Phase Diagrams and Tricritical Behaviour of the Spin-2 Ising Model in a Longitudinal Random Field

    Institute of Scientific and Technical Information of China (English)

    LIANG Ya-Qiu; WEI Guo-Zhu; ZHANG Qi; SONG Guo-Li

    2004-01-01

    @@ Within the framework of the effective-field theory with correlations, we study the ferromagnetic spin-2 randomfield Ising model (RFIM) in the presence of a crystal field on honeycomb (z = 3), square (z = 4) and simple cubic (z = 6) lattices. The effects of the crystal field and the longitudinal random field on the phase diagrams are investigated. Some characteristic features of the phase diagrams, such as the tricritical phenomena, reentrant phenomena and existence of two tricritical points, are found.

  9. The Ising model as a playground for the study of wetting and interface behavior

    OpenAIRE

    Landau, D.P.; Ferrenberg, Alan M.; Binder, K.

    2000-01-01

    Computer simulations have played an important role in the elucidation of wetting and interface unbinding phenomena. In particular, use of the Ising-lattice-gas model in a film geometry and subject to diverse surface and bulk magnetic fields has permitted extensive Monte Carlo simulations to reveal new features of the phase diagrams associated with these phenomena and to provoke new theoretical studies. The status of our knowledge about the nature of wetting and interface-delocalization transi...

  10. Fast vectorized algorithm for the Monte Carlo Simulation of the Random Field Ising Model

    CERN Document Server

    Rieger, H

    1992-01-01

    An algoritm for the simulation of the 3--dimensional random field Ising model with a binary distribution of the random fields is presented. It uses multi-spin coding and simulates 64 physically different systems simultaneously. On one processor of a Cray YMP it reaches a speed of 184 Million spin updates per second. For smaller field strength we present a version of the algorithm that can perform 242 Million spin updates per second on the same machine.

  11. Critical slowing down of cluster algorithms for Ising models coupled to 2-d gravity

    Science.gov (United States)

    Bowick, Mark; Falcioni, Marco; Harris, Geoffrey; Marinari, Enzo

    1994-02-01

    We simulate single and multiple Ising models coupled to 2-d gravity using both the Swendsen-Wang and Wolff algorithms to update the spins. We study the integrated autocorrelation time and find that there is considerable critical slowing down, particularly in the magnetization. We argue that this is primarily due to the local nature of the dynamical triangulation algorithm and to the generation of a distribution of baby universes which inhibits cluster growth.

  12. Critical Slowing Down of Cluster Algorithms for Ising Models Coupled to 2-d Gravity

    CERN Document Server

    Bowick, M; Harris, G; Marinari, E

    1994-01-01

    We simulate single and multiple Ising models coupled to 2-d gravity using both the Swendsen-Wang and Wolff algorithms to update the spins. We study the integrated autocorrelation time and find that there is considerable critical slowing down, particularly in the magnetization. We argue that this is primarily due to the local nature of the dynamical triangulation algorithm and to the generation of a distribution of baby universes which inhibits cluster growth.

  13. Single-cluster algorithm for the site-bond-correlated Ising model

    Science.gov (United States)

    Campos, P. R. A.; Onody, R. N.

    1997-12-01

    We extend the Wolff algorithm to include correlated spin interactions in diluted magnetic systems. This algorithm is applied to study the site-bond-correlated Ising model on a two-dimensional square lattice. We use a finite-size scaling procedure to obtain the phase diagram in the temperature-concentration space. We also have verified that the autocorrelation time diminishes in the presence of dilution and correlation, showing that the Wolff algorithm performs even better in such situations.

  14. Anisotropy of the interface tension of the three-dimensional Ising model

    OpenAIRE

    Bittner, E.; Nußbaumer, A.; W. Janke

    2009-01-01

    We determine the interface tension for the 100, 110 and 111 interface of the simple cubic Ising model with nearest-neighbour interaction using novel simulation methods. To overcome the droplet/strip transition and the droplet nucleation barrier we use a newly developed combination of the multimagnetic algorithm with the parallel tempering method. We investigate a large range of inverse temperatures to study the anisotropy of the interface tension in detail.

  15. Finite Size Scaling and "perfect" actions the three dimensional Ising model

    CERN Document Server

    Ballesteros, H G; Martín-Mayor, V; Muñoz-Sudupe, A

    1998-01-01

    Using Finite-Size Scaling techniques, we numerically show that the first irrelevant operator of the lattice $\\lambda\\phi^4$ theory in three dimensions is (within errors) completely decoupled at $\\lambda=1.0$. This interesting result also holds in the Thermodynamical Limit, where the renormalized coupling constant shows an extraordinary reduction of the scaling-corrections when compared with the Ising model. It is argued that Finite-Size Scaling analysis can be a competitive method for finding improved actions.

  16. On bimodal size distribution of spin clusters in the one dimensional Ising model

    OpenAIRE

    Ivanytskyi, A. I.; Chelnokov, V. O.

    2015-01-01

    The size distribution of geometrical spin clusters is exactly found for the one dimensional Ising model of finite extent. For the values of lattice constant $\\beta$ above some "critical value" $\\beta_c$ the found size distribution demonstrates the non-monotonic behavior with the peak corresponding to the size of largest available cluster. In other words, at high values of lattice constant there are two ways to fill the lattice: either to form a single largest cluster or to create many cluster...

  17. Excited TBA equations II: massless flow from tricritical to critical Ising model

    Energy Technology Data Exchange (ETDEWEB)

    Pearce, Paul A. E-mail: p.pearce@ms.unimelb.edu.au; Chim, Leung E-mail: leung.chim@dsto.defence.gov.au; Ahn, Changrim E-mail: ahn@dante.ewha.ac.kr

    2003-06-16

    We consider the massless tricritical Ising model M(4,5) perturbed by the thermal operator phi (cursive,open) Greek{sub 1,3} in a cylindrical geometry and apply integrable boundary conditions, labelled by the Kac labels (r,s), that are natural off-critical perturbations of known conformal boundary conditions. We derive massless thermodynamic Bethe ansatz (TBA) equations for all excitations by solving, in the continuum scaling limit, the TBA functional equation satisfied by the double-row transfer matrices of the A{sub 4} lattice model of Andrews, Baxter and Forrester (ABF) in Regime IV. The resulting TBA equations describe the massless renormalization group flow from the tricritical to critical Ising model. As in the massive case of Part I, the excitations are completely classified in terms of (m,n) systems but the string content changes by one of three mechanisms along the flow. Using generalized q-Vandermonde identities, we show that this leads to a flow from tricritical to critical Ising characters. The excited TBA equations are solved numerically to follow the continuous flows from the UV to the IR conformal fixed points.

  18. Algorithmic modeling of the irrelevant sound effect (ISE) by the hearing sensation fluctuation strength.

    Science.gov (United States)

    Schlittmeier, Sabine J; Weissgerber, Tobias; Kerber, Stefan; Fastl, Hugo; Hellbrück, Jürgen

    2012-01-01

    Background sounds, such as narration, music with prominent staccato passages, and office noise impair verbal short-term memory even when these sounds are irrelevant. This irrelevant sound effect (ISE) is evoked by so-called changing-state sounds that are characterized by a distinct temporal structure with varying successive auditory-perceptive tokens. However, because of the absence of an appropriate psychoacoustically based instrumental measure, the disturbing impact of a given speech or nonspeech sound could not be predicted until now, but necessitated behavioral testing. Our database for parametric modeling of the ISE included approximately 40 background sounds (e.g., speech, music, tone sequences, office noise, traffic noise) and corresponding performance data that was collected from 70 behavioral measurements of verbal short-term memory. The hearing sensation fluctuation strength was chosen to model the ISE and describes the percept of fluctuations when listening to slowly modulated sounds (f(mod) sounds, the algorithm estimated behavioral performance data in 63 of 70 cases within the interquartile ranges. In particular, all real-world sounds were modeled adequately, whereas the algorithm overestimated the (non-)disturbance impact of synthetic steady-state sounds that were constituted by a repeated vowel or tone. Implications of the algorithm's strengths and prediction errors are discussed.

  19. Monte Carlo renormalization: the triangular Ising model as a test case.

    Science.gov (United States)

    Guo, Wenan; Blöte, Henk W J; Ren, Zhiming

    2005-04-01

    We test the performance of the Monte Carlo renormalization method in the context of the Ising model on a triangular lattice. We apply a block-spin transformation which allows for an adjustable parameter so that the transformation can be optimized. This optimization purportedly brings the fixed point of the transformation to a location where the corrections to scaling vanish. To this purpose we determine corrections to scaling of the triangular Ising model with nearest- and next-nearest-neighbor interactions by means of transfer-matrix calculations and finite-size scaling. We find that the leading correction to scaling just vanishes for the nearest-neighbor model. However, the fixed point of the commonly used majority-rule block-spin transformation appears to lie well away from the nearest-neighbor critical point. This raises the question whether the majority rule is suitable as a renormalization transformation, because the standard assumptions of real-space renormalization imply that corrections to scaling vanish at the fixed point. We avoid this inconsistency by means of the optimized transformation which shifts the fixed point back to the vicinity of the nearest-neighbor critical Hamiltonian. The results of the optimized transformation in terms of the Ising critical exponents are more accurate than those obtained with the majority rule.

  20. Renyi Correlations and Phase Transitions in the Transverse-Field Ising model

    Science.gov (United States)

    Singh, Rajiv; Devakul, Trithep

    2015-03-01

    We calculate T = 0 spin-spin correlation functions with respect to a probability distribution given by an integer power (n) of the reduced density matrix ρcirc;A, when a transverse-field Ising model (TFIM) system is bipartitioned by a planar interface. Using series expansion methods these calculations are done in the thermodynamic limit for arbitrary positive integer n, with n = 1 giving us the bulk correlations. We study the TFIM system on isotropic and anisotropic simple-cubic lattices. We examine the evidence for whether the critical point of the transition deviates from the bulk critical point as a function of n and whether the critical behavior lies in the 2 D or 4 D Ising universality classes as would be expected from a surface transition at finite temperature and a T = 0 bulk transition, respectively. Work supported in part by NSF Grant Number DMR-1306048.

  1. Ising Spin Network States for Loop Quantum Gravity: a Toy Model for Phase Transitions

    CERN Document Server

    Feller, Alexandre

    2015-01-01

    Non-perturbative approaches to quantum gravity call for a deep understanding of the emergence of geometry and locality from the quantum state of the gravitational field. Without background geometry, the notion of distance should entirely emerge from the correlations between the gravity fluctuations. In the context of loop quantum gravity, quantum states of geometry are defined as spin networks. These are graphs decorated with spin and intertwiners, which represent quantized excitations of areas and volumes of the space geometry. Here, we develop the condensed matter point of view on extracting the physical and geometrical information out of spin network states: we introduce new Ising spin network states, both in 2d on a square lattice and in 3d on a hexagonal lattice, whose correlations map onto the usual Ising model in statistical physics. We construct these states from the basic holonomy operators of loop gravity and derive a set of local Hamiltonian constraints which entirely characterize our states. We di...

  2. Effective field study of ising model on a double perovskite structure

    Science.gov (United States)

    Ngantso, G. Dimitri; El Amraoui, Y.; Benyoussef, A.; El Kenz, A.

    2017-02-01

    By using the effective field theory (EFT), the mixed spin-1/2 and spin-3/2 Ising ferrimagnetic model adapted to a double perovskite structure has been studied. The EFT calculations have been carried out from Ising Hamiltonian by taking into account first and second nearest-neighbors interactions and the crystal and external magnetic fields. Both first- and second-order phase transitions have been found in phase diagrams of interest. Depending on crystal-field values, the thermodynamic behavior of total magnetization indicated the compensation phenomenon existence. The hysteresis behaviors are studied by investigating the reduced magnetic field dependence of total magnetization and a series of hysteresis loops are shown for different reduced temperatures around the critical one.

  3. A Non-Perturbative Approach to the Random-Bond Ising Model

    CERN Document Server

    Cabra, D C; Mussardo, G; Pujol, P

    1997-01-01

    We study the N -> 0 limit of the O(N) Gross-Neveu model in the framework of the massless form-factor approach. This model is related to the continuum limit of the Ising model with random bonds via the replica method. We discuss how this method may be useful in calculating correlation functions of physical operators. The identification of non-perturbative fixed points of the O(N) Gross-Neveu model is pursued by its mapping to a WZW model.

  4. Nonequilibrium critical dynamics of the two-dimensional Ising model quenched from a correlated initial state.

    Science.gov (United States)

    Környei, László; Pleimling, Michel; Iglói, Ferenc

    2008-01-01

    The universality class, even the order of the transition, of the two-dimensional Ising model depends on the range and the symmetry of the interactions (Onsager model, Baxter-Wu model, Turban model, etc.), but the critical temperature is generally the same due to self-duality. Here we consider a sudden change in the form of the interaction and study the nonequilibrium critical dynamical properties of the nearest-neighbor model. The relaxation of the magnetization and the decay of the autocorrelation function are found to display a power law behavior with characteristic exponents that depend on the universality class of the initial state.

  5. Multi-GPU Accelerated Multi-Spin Monte Carlo Simulations of the 2D Ising Model

    CERN Document Server

    Block, Benjamin; Preis, Tobias; 10.1016/j.cpc.2010.05.005

    2010-01-01

    A modern graphics processing unit (GPU) is able to perform massively parallel scientific computations at low cost. We extend our implementation of the checkerboard algorithm for the two dimensional Ising model [T. Preis et al., J. Comp. Phys. 228, 4468 (2009)] in order to overcome the memory limitations of a single GPU which enables us to simulate significantly larger systems. Using multi-spin coding techniques, we are able to accelerate simulations on a single GPU by factors up to 35 compared to an optimized single Central Processor Unit (CPU) core implementation which employs multi-spin coding. By combining the Compute Unified Device Architecture (CUDA) with the Message Parsing Interface (MPI) on the CPU level, a single Ising lattice can be updated by a cluster of GPUs in parallel. For large systems, the computation time scales nearly linearly with the number of GPUs used. As proof of concept we reproduce the critical temperature of the 2D Ising model using finite size scaling techniques.

  6. Destroying a topological quantum bit by condensing Ising vortices.

    Science.gov (United States)

    Hao, Zhihao; Inglis, Stephen; Melko, Roger

    2014-12-09

    The imminent realization of topologically protected qubits in fabricated systems will provide not only an elementary implementation of fault-tolerant quantum computing architecture, but also an experimental vehicle for the general study of topological order. The simplest topological qubit harbours what is known as a Z2 liquid phase, which encodes information via a degeneracy depending on the system's topology. Elementary excitations of the phase are fractionally charged objects called spinons, or Ising flux vortices called visons. At zero temperature, a Z2 liquid is stable under deformations of the Hamiltonian until spinon or vison condensation induces a quantum-phase transition destroying the topological order. Here we use quantum Monte Carlo to study a vison-induced transition from a Z2 liquid to a valence-bond solid in a quantum dimer model on the kagome lattice. Our results indicate that this critical point is beyond the description of the standard Landau paradigm.

  7. Nonequilibrium dynamics of an exactly solvable Ising-like model and protein translocation

    CERN Document Server

    Pelizzola, A

    2013-01-01

    Using an Ising-like model of protein mechanical unfolding, we introduce a diffusive dynamics on its exactly known free energy profile, reducing the nonequilibrium dynamics of the model to a biased random walk. As an illustration, the model is then applied to the protein translocation phenomenon, taking inspiration from a recent experiment on the green fluorescent protein pulled by a molecular motor. The average translocation time is evaluated exactly, and the analysis of single trajectories shows that translocation proceeds through an intermediate state, similar to that observed in the experiment.

  8. The Peculiar Phase Transitions of the Ising Model on a Small-World Network

    Science.gov (United States)

    Brunson, Trent; Boettcher, Stefan

    2009-11-01

    To describe many collective phenomena on networks, the Ising model again plays a fundamental role. Here, we study a new network with small-world properties that can be studied exactly with the renormalization group. The network is non-planar and has a recursive design combining a one-dimensional backbone with a hierarchy of long-range bonds. Varying the relative strength between nearest-neighbor and long-range bonds, we can define a one-parameter family of models that exhibits a rich variety of critical phenomena, quite distinct from those on lattice models. Exact results and numerical simulations reveal this behavior in great detail.

  9. Boundary magnetization of a two-dimensional Ising model with inhomogeneous nearest-neighbor interactions

    Science.gov (United States)

    Pelizzola, Alessandro

    1994-11-01

    An explicit formula for the boundary magnetization of a two-dimensional Ising model with a strip of inhomogeneous interactions is obtained by means of a transfer matrix mean-field method introduced by Lipowski and Suzuki. There is clear numerical evidence that the formula is exact By taking the limit where the width of the strip approaches infinity and the interactions have well defined bulk limits, I arrive at the boundary magnetization for a model which includes the Hilhorst-van Leeuwen model. The rich critical behavior of the latter magnetization is thereby rederived with little effort.

  10. Study of Depolarization Field Influence on Ferroelectric Films Within Transverse Ising Model

    Institute of Scientific and Technical Information of China (English)

    TAO Yong-Mei; SHI Qin-Fen; JIANG Qing

    2005-01-01

    An improved transverse Ising model is proposed by taking the depolarization field effect into account.Within the framework of mean-field theory we investigate the behavior of the ferroelectric thin film. Our results show that the influence of the depolarization field is to flatten the spontaneous polarization profile and make the films more homogeneous, which is consistent with Ginzburg-Landau theory. This fact shows that this model can be taken as an effective model to deal with the ferroelectric film and can be further extended to refer to quantum effect. The competition between quantum effect and depolarization field induces some interesting phenomena on ferroelectric thin films.

  11. Phase transition of p-adic Ising λ-model

    Energy Technology Data Exchange (ETDEWEB)

    Dogan, Mutlay; Akın, Hasan [Department of Mathematics, Faculty of Education, Zirve University, Gaziantep, TR27260 (Turkey); Mukhamedov, Farrukh [Department of Computational & Theoretical Sciences Faculty of Science, International Islamic University Malaysia P.O. Box, 141, 25710, Kuantan Pahang (Malaysia)

    2015-09-18

    We consider an interaction of the nearest-neighbors and next nearest-neighbors for the mixed type p-adic λ-model with spin values (−1, +1) on a Cayley tree of order two. In the previous work we have proved the existence of the p-adic Gibbs measure for the model. In this work we have proved the existence of the phase transition occurs for the model.

  12. History of the Lenz–Ising model 1965–1971

    DEFF Research Database (Denmark)

    Niss, Martin

    2011-01-01

    was advanced by Benjamin Widom and others, were confronted with numerical results for the model, in particular the model’s so-called critical exponents. A positive result of a confrontation was seen as positive evidence for this hypothesis. The model was also used to gain insight into specific aspects...

  13. On the hysteresis behaviors of the higher spin Ising model

    Science.gov (United States)

    Akıncı, Ümit

    2017-10-01

    Hysteresis characteristics of the general Spin-S (S > 1) Blume-Capel model have been studied within the effective field approximation. Particular emphasis has been paid on the large negative valued crystal field region and it has been demonstrated for this region that, Spin-S Blume-Capel model has 2 S windowed hysteresis loop in low temperatures. Some interesting results have been obtained such as nested characteristics of the hysteresis loops of successive spin-S Blume-Capel model. Effect of the rising crystal field and temperature on these hysteresis behaviors have been investigated in detail and physical mechanisms have been given.

  14. Understanding localisation in QCD through an Ising-Anderson model

    CERN Document Server

    Giordano, Matteo; Pittler, Ferenc

    2014-01-01

    Above the QCD chiral crossover temperature, the low-lying eigenmodes of the Dirac operator are localised, while moving up in the spectrum states become extended. This localisation/delocalisation transition has been shown to be a genuine second-order phase transition, in the same universality class as that of the 3D Anderson model. The existence of localised modes and the effective dimensional reduction can be tentatively explained as a consequence of local fluctuations of the Polyakov loop, that provide 3D on-site disorder, in analogy to the on-site disorder of the Anderson model. To test the viability of this explanation we study a 3D effective, Anderson-like model, with on-site disorder provided by the spins of a spin model, which mimics the Polyakov loop dynamics. Our preliminary results show that localised modes are present in the ordered phase, thus supporting the proposed mechanism for localisation in QCD.

  15. Comparison of the dipolar magnetic field generated by two Ising-like models

    Science.gov (United States)

    Peqini, Klaudio; Duka, Bejo

    2015-04-01

    We consider two Ising-like models named respectively the "domino" model and the Rikitake disk dynamo model. Both models are based on some collective interactions that can generate a dipolar magnetic field which reproduces the well-known features of the geomagnetic field: the reversals and secular variation (SV). The first model considers the resultant dipolar magnetic field as formed by the superposition of the magnetic fields generated by the dynamo elements called macrospins, while the second one, starting from the two-disk dynamo action, takes in consideration the collective interactions of several disk dynamo elements. We will apply two versions of each model: the short-range and the long-range coupled dynamo elements. We will study the statistical properties of the time series generated by the simulation of all models. The comparison of these results with the paleomagnetic data series and long series of SV enables us to conclude which of these Ising-like models better match with the geomagnetic field time series. Key words: geomagnetic field, domino model, Rikitake disk dynamo, dipolar moment

  16. Minimal duality breaking in the Kallen Lehman approach to 3D Ising model: A numerical test

    Science.gov (United States)

    Astorino, Marco; Canfora, Fabrizio; Martínez, Cristián; Parisi, Luca

    2008-06-01

    A Kallen-Lehman approach to 3D Ising model is analyzed numerically both at low and high temperatures. It is shown that, even assuming a minimal duality breaking, one can fix three parameters of the model to get a very good agreement with the Monte Carlo results at high temperatures. With the same parameters the agreement is satisfactory both at low and near critical temperatures. How to improve the agreement with Monte Carlo results by introducing a more general duality breaking is shortly discussed.

  17. Two-Dimensional Wang-Landau Sampling of AN Asymmetric Ising Model

    Science.gov (United States)

    Tsai, Shan-Ho; Wang, Fugao; Landau, D. P.

    We study the critical endpoint behavior of an asymmetric Ising model with two- and three-body interactions on a triangular lattice, in the presence of an external field. We use a two-dimensional Wang-Landau sampling method to determine the density of states for this model. An accurate density of states allowed us to map out the phase diagram accurately and observe a clear divergence of the curvature of the spectator phase boundary and of the derivative of the magnetization coexistence diameter near the critical endpoint, in agreement with previous theoretical predictions.

  18. Infinite disorder and correlation fixed point in the Ising model with correlated disorder

    Science.gov (United States)

    Chatelain, Christophe

    2017-03-01

    Recent Monte Carlo simulations of the q-state Potts model with a disorder displaying slowly-decaying correlations reported a violation of hyperscaling relation caused by large disorder fluctuations and the existence of a Griffiths phase, as in random systems governed by an infinite-disorder fixed point. New simulations of the Ising model (q = 2), directly made in the limit of an infinite disorder strength, are presented. The magnetic scaling dimension is shown to correspond to the correlated percolation fixed point. The latter is shown to be unstable at finite disorder strength but with a large cross-over length which is not accessible to Monte Carlo simulations.

  19. Variational Monte Carlo study of a gapless spin liquid in the spin-1/2 XXZ antiferromagnetic model on the kagome lattice

    Science.gov (United States)

    Hu, Wen-Jun; Gong, Shou-Shu; Becca, Federico; Sheng, D. N.

    2015-11-01

    By using the variational Monte Carlo technique, we study the spin-1/2 XXZ antiferromagnetic model (with easy-plane anisotropy) on the kagome lattice. A class of Gutzwiller projected fermionic states with a spin Jastrow factor is considered to describe either spin liquids [with U (1 ) or Z2 symmetry] or magnetically ordered phases [with q =(0 ,0 ) or q =(4 π /3 ,0 ) ]. We find that the magnetic states are not stable in the thermodynamic limit. Moreover, there is no energy gain to break the gauge symmetry from U (1 ) to Z2 within the spin-liquid states, as previously found in the Heisenberg model. The best variational wave function is therefore the U (1 ) Dirac state, supplemented by the spin Jastrow factor. Furthermore, a vanishing S =2 spin gap is obtained at the variational level, in the whole regime from the X Y to the Heisenberg model.

  20. Interface localization in the 2D Ising model with a driven line

    Science.gov (United States)

    Cohen, O.; Mukamel, D.

    2016-04-01

    We study the effect of a one-dimensional driving field on the interface between two coexisting phases in a two dimensional model. This is done by considering an Ising model on a cylinder with Glauber dynamics in all sites and additional biased Kawasaki dynamics in the central ring. Based on the exact solution of the two-dimensional Ising model, we are able to compute the phase diagram of the driven model within a special limit of fast drive and slow spin flips in the central ring. The model is found to exhibit two phases where the interface is pinned to the central ring: one in which it fluctuates symmetrically around the central ring and another where it fluctuates asymmetrically. In addition, we find a phase where the interface is centered in the bulk of the system, either below or above the central ring of the cylinder. In the latter case, the symmetry breaking is ‘stronger’ than that found in equilibrium when considering a repulsive potential on the central ring. This equilibrium model is analyzed here by using a restricted solid-on-solid model.

  1. Monte Carlo Studies of Phase Separation in Compressible 2-dim Ising Models

    Science.gov (United States)

    Mitchell, S. J.; Landau, D. P.

    2006-03-01

    Using high resolution Monte Carlo simulations, we study time-dependent domain growth in compressible 2-dim ferromagnetic (s=1/2) Ising models with continuous spin positions and spin-exchange moves [1]. Spins interact with slightly modified Lennard-Jones potentials, and we consider a model with no lattice mismatch and one with 4% mismatch. For comparison, we repeat calculations for the rigid Ising model [2]. For all models, large systems (512^2) and long times (10^ 6 MCS) are examined over multiple runs, and the growth exponent is measured in the asymptotic scaling regime. For the rigid model and the compressible model with no lattice mismatch, the growth exponent is consistent with the theoretically expected value of 1/3 [1] for Model B type growth. However, we find that non-zero lattice mismatch has a significant and unexpected effect on the growth behavior.Supported by the NSF.[1] D.P. Landau and K. Binder, A Guide to Monte Carlo Simulations in Statistical Physics, second ed. (Cambridge University Press, New York, 2005).[2] J. Amar, F. Sullivan, and R.D. Mountain, Phys. Rev. B 37, 196 (1988).

  2. Bayesian Modeling of ChIP-chip Data Through a High-Order Ising Model

    KAUST Repository

    Mo, Qianxing

    2010-01-29

    ChIP-chip experiments are procedures that combine chromatin immunoprecipitation (ChIP) and DNA microarray (chip) technology to study a variety of biological problems, including protein-DNA interaction, histone modification, and DNA methylation. The most important feature of ChIP-chip data is that the intensity measurements of probes are spatially correlated because the DNA fragments are hybridized to neighboring probes in the experiments. We propose a simple, but powerful Bayesian hierarchical approach to ChIP-chip data through an Ising model with high-order interactions. The proposed method naturally takes into account the intrinsic spatial structure of the data and can be used to analyze data from multiple platforms with different genomic resolutions. The model parameters are estimated using the Gibbs sampler. The proposed method is illustrated using two publicly available data sets from Affymetrix and Agilent platforms, and compared with three alternative Bayesian methods, namely, Bayesian hierarchical model, hierarchical gamma mixture model, and Tilemap hidden Markov model. The numerical results indicate that the proposed method performs as well as the other three methods for the data from Affymetrix tiling arrays, but significantly outperforms the other three methods for the data from Agilent promoter arrays. In addition, we find that the proposed method has better operating characteristics in terms of sensitivities and false discovery rates under various scenarios. © 2010, The International Biometric Society.

  3. Network inference using asynchronously updated kinetic Ising Model

    CERN Document Server

    Zeng, Hong-Li; Alava, Mikko; Mahmoudi, Hamed

    2010-01-01

    Network structures are reconstructed from dynamical data by respectively naive mean field (nMF) and Thouless-Anderson-Palmer (TAP) approximations. For TAP approximation, we use two methods to reconstruct the network: a) iteration method; b) casting the inference formula to a set of cubic equations and solving it directly. We investigate inference of the asymmetric Sherrington- Kirkpatrick (S-K) model using asynchronous update. The solutions of the sets cubic equation depend of temperature T in the S-K model, and a critical temperature Tc is found around 2.1. For T Tc there are three real roots. The iteration method is convergent only if the cubic equations have three real solutions. The two methods give same results when the iteration method is convergent. Compared to nMF, TAP is somewhat better at low temperatures, but approaches the same performance as temperature increase. Both methods behave better for longer data length, but for improvement arises, TAP is well pronounced.

  4. Critical behavior of the mixed-spin Ising model with two competing dynamics.

    Science.gov (United States)

    Godoy, Mauricio; Figueiredo, Wagner

    2002-02-01

    In this work we investigate the stationary states of a nonequilibrium mixed-spin Ising model on a square lattice. The model system consists of two interpenetrating sublattices of spins sigma=1/2 and S=1, and we take only nearest neighbor interactions between pairs of spins. The system is in contact with a heat bath at temperature T and subject to an external flux of energy. The contact with the heat bath is simulated by single spin flips according to the Metropolis rule, while the input of energy is mimicked by the simultaneous flipping of pairs of neighboring spins. We performed Monte Carlo simulations on this model in order to find its phase diagram in the plane of temperature T versus the competition parameter between one- and two-spin flips, p. The phase diagram of the model exhibits two ordered phases with sublattice magnetizations m(1), m(2)>0 and m(1)>0, m(2)model belongs to the universality class of the two-dimensional equilibrium Ising model.

  5. Phase Transitions for Quantum Markov Chains Associated with Ising Type Models on a Cayley Tree

    Science.gov (United States)

    Mukhamedov, Farrukh; Barhoumi, Abdessatar; Souissi, Abdessatar

    2016-05-01

    The main aim of the present paper is to prove the existence of a phase transition in quantum Markov chain (QMC) scheme for the Ising type models on a Cayley tree. Note that this kind of models do not have one-dimensional analogous, i.e. the considered model persists only on trees. In this paper, we provide a more general construction of forward QMC. In that construction, a QMC is defined as a weak limit of finite volume states with boundary conditions, i.e. QMC depends on the boundary conditions. Our main result states the existence of a phase transition for the Ising model with competing interactions on a Cayley tree of order two. By the phase transition we mean the existence of two distinct QMC which are not quasi-equivalent and their supports do not overlap. We also study some algebraic property of the disordered phase of the model, which is a new phenomena even in a classical setting.

  6. Spontaneous alignment of frustrated bonds in an anisotropic, three-dimensional Ising model

    Science.gov (United States)

    Jalabert, Rodolfo A.; Sachdev, Subir

    1991-07-01

    The Ising model on a three-dimensional cubic lattice with all plaquettes in the x-y frustrated plane is studied by use of a Monte Carlo technique; the exchange constants are of equal magnitude, but have varying signs. At zero temperature, the model has a finite entropy and no long-range order. The low-temperature phase is characterized by an order parameter measuring the openZ4 symmetry of lattice rotations which is invariant under Mattis gauge transformation; fluctuations lead to the alignment of frustrated bonds into columns and a fourfold degeneracy. An additional factor-of-2 degeneracy is obtained from a global spin flip. The order vanishes at a critical temperature by a transition that appears to be in the universality class of the D=3, XY model. These results are consistent with the theoretical predictions of Blankschtein et al. This Ising model is related by duality to phenomenological models of two-dimensional frustrated quantum antiferromagnets.

  7. The density of states for an antiferromagnetic Ising model on a triangular lattice

    Institute of Scientific and Technical Information of China (English)

    XIA Kai; YAO Xiao-yan; LIU Jun-ming

    2007-01-01

    The Wang-Landau algorithm is an efficient Monte Carlo approach to the density of states of a statistical mechanics system.The estimation of state density would allow the computation of thermodynamic properties of the system over the whole temperature range.We apply this sampling method to study the phase transitions in a triangular Ising model.The entropy of the lattice at zero temperature as well as other thermodynamic properties is computed.The calculated thermodynamic properties are explained in the context of the magnetic phase transition.

  8. Entanglement entropy through conformal interfaces in the 2D Ising model

    CERN Document Server

    Brehm, Enrico M

    2015-01-01

    We consider the entanglement entropy for the 2D Ising model at the conformal fixed point in the presence of interfaces. More precisely, we investigate the situation where the two subsystems are separated by a defect line that preserves conformal invariance. Using the replica trick, we compute the entanglement entropy between the two subsystems. We observe that the entropy, just like in the case without defects, shows a logarithmic scaling behavior with respect to the size of the system. Here, the prefactor of the logarithm depends on the strength of the defect encoded in the transmission coefficient. We also commend on the supersymmetric case.

  9. Investigation of probability theory on Ising models with different four-spin interactions

    Science.gov (United States)

    Yang, Yuming; Teng, Baohua; Yang, Hongchun; Cui, Haijuan

    2017-10-01

    Based on probability theory, two types of three-dimensional Ising models with different four-spin interactions are studied. Firstly the partition function of the system is calculated by considering the local correlation of spins in a given configuration, and then the properties of the phase transition are quantitatively discussed with series expansion technique and numerical method. Meanwhile the rounding errors in this calculation is analyzed so that the possibly source of the error in the calculation based on the mean field theory is pointed out.

  10. Interface delocalization in the three-dimensional Ising model with a defect plane

    Science.gov (United States)

    Benyoussef, A.; El Kenz, A.

    1993-02-01

    Using mean-field theory, the finite-cluster approximation, and the real-space renormalization group, we study the spin-1/2 Ising model on a cubic lattice with a defect plane that divides the system into two semi-infinite ones. The phase diagrams, which represent the connection between defect-plane order and wetting phenomena, are given in the case of two equivalent semi-infinite systems (the same coupling) and in the case of different semi-infinite systems. These phase diagrams are in agreement with those conjectured qualitatively by Igloi and Indekeu.

  11. Approximating the Ising model on fractal lattices of dimension less than two

    DEFF Research Database (Denmark)

    Codello, Alessandro; Drach, Vincent; Hietanen, Ari

    2015-01-01

    We construct periodic approximations to the free energies of Ising models on fractal lattices of dimension smaller than two, in the case of a zero external magnetic field, based on the combinatorial method of Feynman and Vdovichenko. We show that the procedure is applicable to any fractal obtained...... with, possibly, arbitrary accuracy and paves the way for determination Tc of any fractal of dimension less than two. Critical exponents are more diffcult to determine since the free energy of any periodic approximation still has a logarithmic singularity at the critical point implying α = 0. We also...

  12. Critical behavior of the Ising model on a hierarchical lattice with aperiodic interactions

    Science.gov (United States)

    Pinho, S. T. R.; Haddad, T. A. S.; Salinas, S. R.

    We write the exact renormalization-group recursion relations for nearest-neighbor ferromagnetic Ising models on Migdal-Kadanoff hierarchical lattices with a distribution of aperiodic exchange interactions according to a class of substitutional sequences. For small geometric fluctuations, the critical behavior is unchanged with respect to the uniform case. For large fluctuations, as in the case of the Rudin-Shapiro sequence, the uniform fixed point in the parameter space cannot be reached from any physical initial conditions. We derive a criterion to check the relevance of the geometric fluctuations.

  13. Ising model formulation of large scale dynamics universality in the universe

    CERN Document Server

    Goldman, T; Laflamme, R

    1995-01-01

    The partition function of a system of galaxies in gravitational interaction can be cast in an Ising Model form, and this reformulated via a Hubbard--Stratonovich transformation into a three dimensional stochastic and classical scalar field theory, whose critical exponents are calculable and known. This allows one to {\\it compute\\/} the galaxy to galaxy correlation function, whose non--integer exponent is predicted to be between 1.530 and 1.862, to be compared with the phenomenological value of 1.6 to 1.8.

  14. Monte Carlos studies of critical and dynamic phenomena in mixed bond Ising model

    Science.gov (United States)

    Santos-Filho, J. B.; Moreno, N. O.; de Albuquerque, Douglas F.

    2010-11-01

    The phase transition of a random mixed-bond Ising ferromagnet on a cubic lattice model is studied both numerically and analytically. In this work, we use the Metropolis and Wolff algorithm with histogram technique and finite size scaling theory to simulate the dynamics of the system. We obtained the thermodynamic quantities such as magnetization, susceptibility, and specific heat. Our results were compared with those obtained using a new technique in effective field theory that employs similar probability distribution within the framework of two-site clusters.

  15. Phase Diagram and Tricritical Behavior of a Spin-2 Transverse Ising Model in a Random Field

    Institute of Scientific and Technical Information of China (English)

    LIANG Ya-Qiu; WEI Guo-Zhu; SONG Li-Li; SONG Guo-Li; ZANG Shu-Liang

    2004-01-01

    The phase diagrams of a spin-2 transverse Ising model with a random field on honeycomb, square, and simple-cubic lattices, respectively, are investigated within the framework of an effective-field theory with correlations.We find the behavior of the tricritical point and the reentrant phenomenon for the system with any coordination number z, when the applied random field is bimodal. The behavior of the tricritical point is also examined as a function of applied transverse field. The reentrant phenomenon comes from the competition between the transverse field and the random field.

  16. Phenomenological theory of surface effects in ferroelectrics and its relationship with transverse Ising model

    Institute of Scientific and Technical Information of China (English)

    钟维烈; 王玉国; 张沛霖; 曲保东

    1997-01-01

    The relationship between the transverse field Ising model and the Landau phenomenological theory for ferroelectrics is analyzed, and the Landau free energy expression for ferroelectrics having surfaces is derived. It is pointed out that the traditional expression in which the surface integral has only a term of the square polarization is valid only for special cases, in general a term of the polarization to the four should be included as well. By use of the newly derived free energy expression, the thickness-dependence of the spontaneous polarization and Curie temperature of ferroelectric films is calculated; thereby some experimental results incompatible with the traditional phenomenological theory are successfully explained.

  17. Boundary field induced first-order transition in the 2D Ising model: exact study

    Energy Technology Data Exchange (ETDEWEB)

    Clusel, Maxime [Institut Laue-Langevin, 6 rue Horowitz BP156 X, 38042 Grenoble Cedex (France); Fortin, Jean-Yves [Laboratoire Poncelet, 119002, Bolshoy Vlasyevskiy Pereulok 11, Moscow (Russian Federation)

    2006-02-03

    We present in this paper an exact study of a first-order transition induced by an inhomogeneous boundary magnetic field in the 2D Ising model. From a previous analysis of the interfacial free energy in the discrete case (Clusel and Fortin 2005 J. Phys. A: Math. Gen. 38 2849) we identify, using an asymptotic expansion in the thermodynamic limit, the line of transition that separates the regime where the interface is localized near the boundary from the one where it is propagating inside the bulk. In particular, the transition line has a strong dependence on the aspect ratio of the lattice.

  18. A threaded Java concurrent implementation of the Monte-Carlo Metropolis Ising model.

    Science.gov (United States)

    Castañeda-Marroquín, Carlos; de la Puente, Alfonso Ortega; Alfonseca, Manuel; Glazier, James A; Swat, Maciej

    2009-06-01

    This paper describes a concurrent Java implementation of the Metropolis Monte-Carlo algorithm that is used in 2D Ising model simulations. The presented method uses threads, monitors, shared variables and high level concurrent constructs that hide the low level details. In our algorithm we assign one thread to handle one spin flip attempt at a time. We use special lattice site selection algorithm to avoid two or more threads working concurently in the region of the lattice that "belongs" to two or more different spins undergoing spin-flip transformation. Our approach does not depend on the current platform and maximizes concurrent use of the available resources.

  19. Magnetic properties of a transverse spin- Ising model with random longitudinal field

    Science.gov (United States)

    Liang, Ya-Qiu; Wei, Guo-Zhu; Song, Guo-Li

    2004-12-01

    Within the framework of the effective-field theory with correlations, a spin- transverse Ising model in the longitudinal random-field on a honeycomb lattice is studied. The phase diagrams and the behavior of the tricritical point are examined. The possible re-entrance phenomena displayed by the system due to the competition effects that occur for the appropriate ranges of the random and transverse field are investigated. The longitudinal and transverse magnetizations, the longitudinal quadrupolar moments and internal energy are given numerically for a honeycomb lattice (z = 3).

  20. Scaling and universality in the two-dimensional Ising model with a magnetic field.

    Science.gov (United States)

    Mangazeev, Vladimir V; Dudalev, Michael Yu; Bazhanov, Vladimir V; Batchelor, Murray T

    2010-06-01

    The scaling function of the two-dimensional Ising model on the square and triangular lattices is obtained numerically via Baxter's variational corner transfer-matrix approach. The use of Aharony-Fisher nonlinear scaling variables allowed us to perform calculations sufficiently away from the critical point and to confirm all predictions of the scaling and universality hypotheses. Our results are in excellent agreement with quantum field theory calculations of Fonseca and Zamolodchikov as well as with many previously known exact and numerical calculations, including susceptibility results by Barouch, McCoy, Tracy, and Wu.

  1. Criticality in Alternating Layered Ising Models : I. Effects of connectivity and proximity

    OpenAIRE

    Au-Yang, Helen; Fisher, Michael E.

    2013-01-01

    The specific heats of exactly solvable alternating layered planar Ising models with strips of width $m_1$ lattice spacings and ``strong'' couplings $J_1$ sandwiched between strips of width $m_2$ and ``weak'' coupling $J_2$, have been studied numerically to investigate the effects of connectivity and proximity. We find that the enhancements of the specific heats of the strong layers and of the overall or `bulk' critical temperature, $T_c(J_1,J_2;m_1,m_2)$, arising from the collective effects r...

  2. Ground-State Phase Diagram of Transverse Spin-2 Ising Model with Longitudinal Crystal-Field

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The transverse spin-2 Ising ferromagnetic model with a longitudinal crystal-field is studied within the mean-field theory based on Bogoliubov inequality for the Gibbs free energy. The ground-state phase diagram and the tricritical point are obtained in the transverse field Ω/z J-longitudinal crystal D/zJ field plane. We find that there are the first order-order phase transitions in a very smallrange of D/zJ besides the usual first order-disorder phase transitions and the second order-disorder phase transitions.

  3. Phase Diagram of the Two-Dimensional Ising Model with Dipolar Interaction

    Institute of Scientific and Technical Information of China (English)

    SUN Gang; CHU Qian-Jin

    2001-01-01

    We treat the two-dimensional Ising model with the dipolar interaction by the numerical calculation under the restriction that the spin configurations are distributed with a 4 × 4 period. The phase diagram with respect to temperature and dipolar interaction strength is constructed. Most characters of the phase diagram are consistent with those obtained in the references by the Monte Carlo simulation, except that we find a new rectangle phase, which is ordered in the spin structure with the 1 × 2 rectangle.

  4. A theory of solving TAP equations for Ising models with general invariant random matrices

    DEFF Research Database (Denmark)

    Opper, Manfred; Çakmak, Burak; Winther, Ole

    2016-01-01

    We consider the problem of solving TAP mean field equations by iteration for Ising models with coupling matrices that are drawn at random from general invariant ensembles. We develop an analysis of iterative algorithms using a dynamical functional approach that in the thermodynamic limit yields a...... the iteration dependent on a Gaussian distributed field only. The TAP magnetizations are stable fixed points if a de Almeida–Thouless stability criterion is fulfilled. We illustrate our method explicitly for coupling matrices drawn from the random orthogonal ensemble....

  5. Algebraic and group structure for bipartite anisotropic Ising model on a non-local basis

    Science.gov (United States)

    Delgado, Francisco

    2015-01-01

    Entanglement is considered a basic physical resource for modern quantum applications as Quantum Information and Quantum Computation. Interactions based on specific physical systems able to generate and sustain entanglement are subject to deep research to get understanding and control on it. Atoms, ions or quantum dots are considered key pieces in quantum applications because they are elements in the development toward a scalable spin-based quantum computer through universal and basic quantum operations. Ising model is a type of interaction generating entanglement in quantum systems based on matter. In this work, a general bipartite anisotropic Ising model including an inhomogeneous magnetic field is analyzed in a non-local basis. This model summarizes several particular models presented in literature. When evolution is expressed in the Bell basis, it shows a regular block structure suggesting a SU(2) decomposition. Then, their algebraic properties are analyzed in terms of a set of physical parameters which define their group structure. In particular, finite products of pulses in this interaction are analyzed in terms of SU(4) covering. Thus, evolution denotes remarkable properties, in particular those related potentially with entanglement and control, which give a fruitful arena for further quantum developments and generalization.

  6. Classical topological order in kagome ice

    Energy Technology Data Exchange (ETDEWEB)

    Macdonald, Andrew J; Melko, Roger G [Department of Physics and Astronomy, University of Waterloo, ON, N2L 3G1 (Canada); Holdsworth, Peter C W [Universite de Lyon, Laboratoire de Physique, Ecole Normale Superieure de Lyon, CNRS, 46 Allee d' Italie, 69364 Lyon Cedex 07 (France)

    2011-04-27

    We examine the onset of classical topological order in a nearest neighbour kagome ice model. Using Monte Carlo simulations, we characterize the topological sectors of the ground state using a nonlocal cut measure which circumscribes the toroidal geometry of the simulation cell. We demonstrate that simulations which employ global loop updates that are allowed to wind around the periodic boundaries cause the topological sector to fluctuate, while restricted local loop updates freeze the simulation into one topological sector. The freezing into one topological sector can also be observed in the susceptibility of the real magnetic spin vectors projected onto the kagome plane. The ability of the susceptibility to distinguish between fluctuating and non-fluctuating topological sectors should motivate its use as a local probe of topological order in a variety of related systems.

  7. The Random-Bond Ising Model in 2.01 and 3 Dimensions

    CERN Document Server

    Komargodski, Zohar

    2016-01-01

    We consider the Ising model between 2 and 4 dimensions perturbed by quenched disorder in the strength of the interaction between nearby spins. In the interval 2Ising model. We compare these new methods with previous studies. Finally, we comment about the $O(2)$ model in d=3, where we predict a large logarithmic correction to the infrared scaling of disorder.

  8. Quantum correlation and quantum phase transition in the one-dimensional extended Ising model

    Science.gov (United States)

    Zhang, Xi-Zheng; Guo, Jin-Liang

    2017-09-01

    Quantum phase transitions can be understood in terms of Landau's symmetry-breaking theory. Following the discovery of the quantum Hall effect, a new kind of quantum phase can be classified according to topological rather than local order parameters. Both phases coexist for a class of exactly solvable quantum Ising models, for which the ground state energy density corresponds to a loop in a two-dimensional auxiliary space. Motivated by this we study quantum correlations, measured by entanglement and quantum discord, and critical behavior seen in the one-dimensional extended Ising model with short-range interaction. We show that the quantum discord exhibits distinctive behaviors when the system experiences different topological quantum phases denoted by different topological numbers. Quantum discords capability to detect a topological quantum phase transition is more reliable than that of entanglement at both zero and finite temperatures. In addition, by analyzing the divergent behaviors of quantum discord at the critical points, we find that the quantum phase transitions driven by different parameters of the model can also display distinctive critical behaviors, which provides a scheme to detect the topological quantum phase transition in practice.

  9. Mixed Algorithms in the Ising Model on Directed BARABÁSI-ALBERT Networks

    Science.gov (United States)

    Lima, F. W. S.

    On directed Barabási-Albert networks with two and seven neighbours selected by each added site, the Ising model does not seem to show a spontaneous magnetisation. Instead, the decay time for flipping of the magnetisation follows an Arrhenius law for Metropolis and Glauber algorithms, but for Wolff cluster flipping the magnetisation decays exponentially with time. On these networks the magnetisation behaviour of the Ising model, with Glauber, HeatBath, Metropolis, Wolf or Swendsen-Wang algorithm competing against Kawasaki dynamics, is studied by Monte Carlo simulations. We show that the model exhibits the phenomenon of self-organisation (= stationary equilibrium) defined in Ref. 8 when Kawasaki dynamics is not dominant in its competition with Glauber, HeatBath and Swendsen-Wang algorithms. Only for Wolff cluster flipping the magnetisation, this phenomenon occurs after an exponentially decay of magnetisation with time. The Metropolis results are independent of competition. We also study the same process of competition described above but with Kawasaki dynamics at the same temperature as the other algorithms. The obtained results are similar for Wolff cluster flipping, Metropolis and Swendsen-Wang algorithms but different for HeatBath.

  10. The random-bond Ising model in 2.01 and 3 dimensions

    Science.gov (United States)

    Komargodski, Zohar; Simmons-Duffin, David

    2017-04-01

    We consider the Ising model between 2 and 4 dimensions perturbed by quenched disorder in the strength of the interaction between nearby spins. In the interval 2  group. At d  =  2 such disorder is marginally irrelevant and can be studied using conformal perturbation theory. Combining conformal perturbation theory with recent results from the conformal bootstrap we compute some scaling exponents in an expansion around d  =  2. If one trusts these computations also in d  =  3, one finds results consistent with experimental data and Monte Carlo simulations. In addition, we perform a direct uncontrolled computation in d  =  3 using new results for low-lying operator dimensions and OPE coefficients in the 3d Ising model. We compare these new methods with previous studies. Finally, we comment about the O(2) model in d  =  3, where we predict a large logarithmic correction to the infrared scaling of disorder.

  11. Bound states in the 3d Ising model and implications for QCD at finite temperature and density

    CERN Document Server

    Caselle, M; Provero, P; Zarembo, K

    2002-01-01

    We study the spectrum of bound states of the three dimensional Ising model in the (h,beta) plane near the critical point. We show the existence of an unbinding line, defined as the boundary of the region where bound states exist. Numerical evidence suggests that this line coincides with the beta=beta_c axis. When the 3D Ising model is considered as an effective description of hot QCD at finite density, we conjecture the correspondence between the unbinding line and the line that separates the quark-gluon plasma phase from the superconducting phase. The bound states of the Ising model are conjectured to correspond to the diquarks of the latter phase of QCD.

  12. On the solution, the critical exponents and the transition equation of the simple cubic three-dimensional Ising model

    NARCIS (Netherlands)

    Hoede, C.; Zandvliet, H.J.W.

    2008-01-01

    In a recent paper Hoede and Zandvliet introduced the concept of gauging on an equation. This enables the simulation of more complex Ising models by the simple quadratic model. The possibility of simulating the simple cubic model was defended by calculating a sequence of approximations to the transit

  13. A kagome map of spin liquids from XXZ to Dzyaloshinskii–Moriya ferromagnet

    Science.gov (United States)

    Essafi, Karim; Benton, Owen; Jaubert, L.D.C.

    2016-01-01

    Despite its deceptive simplicity, few concepts have more fundamental implications than chirality, from the therapeutic activity of drugs to the fundamental forces of nature. In magnetic materials, chirality gives rise to unconventional phenomena such as the anomalous Hall effect and multiferroicity, taking an enhanced flavour in the so-called spin-liquid phases where magnetic disorder prevails. Kagome systems sit at the crossroad of these ideas. Motivated by the recent synthesis of rare-earth kagome materials and the progresses in optical-lattice experiments, we bring together an entire network of spin liquids with anisotropic and Dzyaloshinskii–Moriya interactions. This network revolves around the Ising antiferromagnet and ends on (ferromagnetic) chiral spin liquids with spontaneously broken time-reversal symmetry. As for the celebrated Heisenberg antiferromagnet, it now belongs to a triad of equivalently disordered phases. The present work provides a unifying theory of kagome spin liquids with time-reversal invariant nearest-neighbour Hamiltonians. PMID:26796866

  14. A kagome map of spin liquids from XXZ to Dzyaloshinskii-Moriya ferromagnet.

    Science.gov (United States)

    Essafi, Karim; Benton, Owen; Jaubert, L D C

    2016-01-22

    Despite its deceptive simplicity, few concepts have more fundamental implications than chirality, from the therapeutic activity of drugs to the fundamental forces of nature. In magnetic materials, chirality gives rise to unconventional phenomena such as the anomalous Hall effect and multiferroicity, taking an enhanced flavour in the so-called spin-liquid phases where magnetic disorder prevails. Kagome systems sit at the crossroad of these ideas. Motivated by the recent synthesis of rare-earth kagome materials and the progresses in optical-lattice experiments, we bring together an entire network of spin liquids with anisotropic and Dzyaloshinskii-Moriya interactions. This network revolves around the Ising antiferromagnet and ends on (ferromagnetic) chiral spin liquids with spontaneously broken time-reversal symmetry. As for the celebrated Heisenberg antiferromagnet, it now belongs to a triad of equivalently disordered phases. The present work provides a unifying theory of kagome spin liquids with time-reversal invariant nearest-neighbour Hamiltonians.

  15. A kagome map of spin liquids from XXZ to Dzyaloshinskii-Moriya ferromagnet

    Science.gov (United States)

    Essafi, Karim; Benton, Owen; Jaubert, L. D. C.

    2016-01-01

    Despite its deceptive simplicity, few concepts have more fundamental implications than chirality, from the therapeutic activity of drugs to the fundamental forces of nature. In magnetic materials, chirality gives rise to unconventional phenomena such as the anomalous Hall effect and multiferroicity, taking an enhanced flavour in the so-called spin-liquid phases where magnetic disorder prevails. Kagome systems sit at the crossroad of these ideas. Motivated by the recent synthesis of rare-earth kagome materials and the progresses in optical-lattice experiments, we bring together an entire network of spin liquids with anisotropic and Dzyaloshinskii-Moriya interactions. This network revolves around the Ising antiferromagnet and ends on (ferromagnetic) chiral spin liquids with spontaneously broken time-reversal symmetry. As for the celebrated Heisenberg antiferromagnet, it now belongs to a triad of equivalently disordered phases. The present work provides a unifying theory of kagome spin liquids with time-reversal invariant nearest-neighbour Hamiltonians.

  16. Quantum Supremacy for Simulating a Translation-Invariant Ising Spin Model

    Science.gov (United States)

    Gao, Xun; Wang, Sheng-Tao; Duan, L.-M.

    2017-01-01

    We introduce an intermediate quantum computing model built from translation-invariant Ising-interacting spins. Despite being nonuniversal, the model cannot be classically efficiently simulated unless the polynomial hierarchy collapses. Equipped with the intrinsic single-instance-hardness property, a single fixed unitary evolution in our model is sufficient to produce classically intractable results, compared to several other models that rely on implementation of an ensemble of different unitaries (instances). We propose a feasible experimental scheme to implement our Hamiltonian model using cold atoms trapped in a square optical lattice. We formulate a procedure to certify the correct functioning of this quantum machine. The certification requires only a polynomial number of local measurements assuming measurement imperfections are sufficiently small.

  17. Can Ising model and/or QKPZ equation properly describe reactive-wetting interface dynamics?

    Science.gov (United States)

    Efraim, Yael; Taitelbaum, Haim

    2009-09-01

    The reactive-wetting process, e.g. spreading of a liquid droplet on a reactive substrate is known as a complex, non-linear process with high sensitivity to minor fluctuations. The dynamics and geometry of the interface (triple line) between the materials is supposed to shed light on the main mechanisms of the process. We recently studied a room temperature reactive-wetting system of a small (˜ 150 μm) Hg droplet that spreads on a thin (˜ 4000 Å) Ag substrate. We calculated the kinetic roughening exponents (growth and roughness), as well as the persistence exponent of points on the advancing interface. In this paper we address the question whether there exists a well-defined model to describe the interface dynamics of this system, by performing two sets of numerical simulations. The first one is a simulation of an interface propagating according to the QKPZ equation, and the second one is a landscape of an Ising chain with ferromagnetic interactions in zero temperature. We show that none of these models gives a full description of the dynamics of the experimental reactivewetting system, but each one of them has certain common growth properties with it. We conjecture that this results from a microscopic behavior different from the macroscopic one. The microscopic mechanism, reflected by the persistence exponent, resembles the Ising behavior, while in the macroscopic scale, exemplified by the growth exponent, the dynamics looks more like the QKPZ dynamics.

  18. Towards an exact solution for the three-dimensional Ising model: A method of the recurrence equations for partial contractions

    Energy Technology Data Exchange (ETDEWEB)

    Kocharovsky, Vitaly V., E-mail: vkochar@physics.tamu.edu [Department of Physics and Astronomy, Texas A& M University, College Station, TX 77843-4242 (United States); Institute of Applied Physics, Russian Academy of Science, 603950 Nizhny Novgorod (Russian Federation); Kocharovsky, Vladimir V. [Institute of Applied Physics, Russian Academy of Science, 603950 Nizhny Novgorod (Russian Federation); Lobachevsky State University of Nizhny Novgorod, 23 Gagarin Avenue, Nizhny Novgorod 603950 (Russian Federation)

    2015-10-16

    We find the exact solutions for the main steps in the analysis of the three-dimensional Ising model. A method is based on a recently found rigorous theory of magnetic phase transitions in a mesoscopic lattice of spins, described as the constrained spin bosons in a Holstein–Primakoff representation. - Highlights: • Main steps towards exact solution of 3D Ising model are outlined. • Rigorous theory of the constrained spin-boson excitations is formulated. • Novel method of the recurrence equations for partial contractions is proposed.

  19. Z2 topological liquid of hard-core bosons on a kagome lattice at 1 /3 filling

    Science.gov (United States)

    Roychowdhury, Krishanu; Bhattacharjee, Subhro; Pollmann, Frank

    2015-08-01

    We consider hard-core bosons on the kagome lattice in the presence of short-range repulsive interactions and focus particularly on the filling factor 1 /3 . In the strongly interacting limit, the low-energy excitations can be described by the quantum fully packed loop coverings on the triangular lattice. Using a combination of tensor product state based methods and exact diagonalization techniques, we show that the system has an extended Z2 topological liquid phase as well as a latti ce nematic phase. The latter breaks lattice rotational symmetry. By tuning appropriate parameters in the model, we study the quantum phase transition between the topological and the symmetry broken phases. We construct the critical theory for this transition using a mapping to an Ising gauge theory that predicts the transition to belong to the O (3 ) universality class.

  20. The high-temperature expansion of the classical Ising model with Sz2 term

    Directory of Open Access Journals (Sweden)

    M.T. Thomaz

    2012-03-01

    Full Text Available We derive the high-temperature expansion of the Helmholtz free energy up to order β17 of the one-dimensional spin-S Ising model, with single-ion anisotropy term, in the presence of a longitudinal magnetic field. We show that the values of some thermodynamical functions for the ferromagnetic models, in the presence of a weak magnetic field, are not small corrections to their values with h=0. This model with S=3 was applied by Kishine et al. [J.-i. Kishine et al., Phys. Rev. B, 2006, 74, 224419] to analyze experimental data of the single-chain magnet [Mn (saltmen]2 [Ni(pac2 (py2] (PF62 for T<40 K. We show that for T<35 K the thermodynamic functions of the large-spin limit model are poor approximations to their analogous spin-3 functions.

  1. Minimalistic real-space renormalization of Ising and Potts Models in two dimensions

    Directory of Open Access Journals (Sweden)

    Gary eWillis

    2015-06-01

    Full Text Available We introduce and discuss a real-space renormalization group (RSRG procedure on very small lattices, which in principle does not require any of the usual approximations, e.g. a cut-off in the expansion of the Hamiltonian in powers of the field. The procedure is carried out numerically on very small lattices (4x4 to 2x2 and implemented for the Ising Model and the q=3,4,5 Potts Models. Nevertheless, the resulting estimates of the correlation length exponent and the magnetization exponent are typically within 3% to 7% of the exact values. The 4-state Potts Model generates a third magnetic exponent which seems to be unknown in the literature. A number of questions about the meaning of certain exponents and the procedure itself arise from its use of symmetry principles and its application to the q=5 Potts Model.

  2. Modified kagome physics in the natural spin-1/2 kagome lattice systems - kapellasite Cu3Zn(OH)6Cl2 and haydeeite Cu3Mg(OH)6Cl2

    OpenAIRE

    Janson, O.; Richter, J.; Rosner, H

    2008-01-01

    The recently discovered natural minerals Cu3Zn(OH)6Cl2 and Cu3Mg(OH)6Cl2 are spin 1/2 systems with an ideal kagome geometry. Based on electronic structure calculations, we develop a realistic model which includes couplings across the kagome hexagons beyond the original kagome model that are intrinsic in real kagome materials. Exact diagonalization studies for the derived model reveal a strong impact of these couplings on the magnetic ground state. Our predictions could be compared to and supp...

  3. Modified kagome physics in the natural spin-1/2 kagome lattice systems: kapellasite Cu3Zn(OH)6Cl2 and haydeeite Cu3Mg(OH)6Cl2.

    Science.gov (United States)

    Janson, O; Richter, J; Rosner, H

    2008-09-05

    The recently discovered natural minerals Cu3Zn(OH)6Cl2 and Cu3Mg(OH)6Cl2 are spin 1/2 systems with an ideal kagome geometry. Based on electronic structure calculations, we develop a realistic model which includes couplings across the kagome hexagons beyond the original kagome model that are intrinsic in real kagome materials. Exact diagonalization studies for the derived model reveal a strong impact of these couplings on the magnetic ground state. Our predictions could be compared to and supplied with neutron scattering, thermodynamic data, and NMR data.

  4. A hidden Ising model for ChIP-chip data analysis

    KAUST Repository

    Mo, Q.

    2010-01-28

    Motivation: Chromatin immunoprecipitation (ChIP) coupled with tiling microarray (chip) experiments have been used in a wide range of biological studies such as identification of transcription factor binding sites and investigation of DNA methylation and histone modification. Hidden Markov models are widely used to model the spatial dependency of ChIP-chip data. However, parameter estimation for these models is typically either heuristic or suboptimal, leading to inconsistencies in their applications. To overcome this limitation and to develop an efficient software, we propose a hidden ferromagnetic Ising model for ChIP-chip data analysis. Results: We have developed a simple, but powerful Bayesian hierarchical model for ChIP-chip data via a hidden Ising model. Metropolis within Gibbs sampling algorithm is used to simulate from the posterior distribution of the model parameters. The proposed model naturally incorporates the spatial dependency of the data, and can be used to analyze data with various genomic resolutions and sample sizes. We illustrate the method using three publicly available datasets and various simulated datasets, and compare it with three closely related methods, namely TileMap HMM, tileHMM and BAC. We find that our method performs as well as TileMap HMM and BAC for the high-resolution data from Affymetrix platform, but significantly outperforms the other three methods for the low-resolution data from Agilent platform. Compared with the BAC method which also involves MCMC simulations, our method is computationally much more efficient. Availability: A software called iChip is freely available at http://www.bioconductor.org/. Contact: moq@mskcc.org. © The Author 2010. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org.

  5. Damage propagation at the interface's localization-delocalization transition of the confined Ising model

    Science.gov (United States)

    Rubio Puzzo, M. Leticia; Albano, Ezequiel V.

    2002-09-01

    The propagation of damage in a confined magnetic Ising film, with short-range competing magnetic fields (h) acting at opposite walls, is studied by means of Monte Carlo simulations. Due to the presence of the fields, the film undergoes a wetting transition at a well-defined critical temperature Tw(h). In fact, the competing fields cause the occurrence of an interface between magnetic domains of different orientations. For TTw(h)] such an interface is bound (unbound) to the walls, while right at Tw(h) the interface is essentially located at the center of the film. It is found that the spatiotemporal spreading of the damage becomes considerably enhanced by the presence of the interface, which acts as a ``catalyst'' of the damage causing an enhancement of the total damaged area. The critical points for damage spreading are evaluated by extrapolation to the thermodynamic limit using a finite-size scaling approach. Furthermore, the wetting transition effectively shifts the location of the damage spreading critical points, as compared with the well-known critical temperature of the order-disorder transition characteristic of the Ising model. Such critical points are found to be placed within the nonwet phase.

  6. The Role of Interfaces in the Propagation of Damage in the Confined Ising Model

    Science.gov (United States)

    Rubio Puzzo, M. Leticia; Albano, Ezequiel V.

    2003-04-01

    The propagation of damage in a confined magnetic Ising film, with short range competing magnetic fields (h) acting at opposite walls, is studied by means of Monte Carlo simulations. Due to the presence of the fields, the film undergoes a wetting transition at a well defined critical temperature Tw(h). In fact, the competing fields causes the occurrence of an interface between magnetic domains of different orientation. For T Tw(h)) such interface is bounded (unbounded) to the walls, while right at Tw(h) the interface is essentially located at the center of the film. It is found that the spatio-temporal spreading of the damage becomes considerably enhanced by the presence of the interface, which act as a "catalyst" of the damage causing an enhancement of the total damaged area. The critical points for damage spreading are evaluated by extrapolation to the thermodynamic limit using a finite-size scaling approach. Furthermore, the wetting transition effectively shifts the location of the damage spreading critical points, as compared with the well known critical temperature of the order-disorder transition characteristic of the Ising model. Such a critical points are found to be placed within the non-wet phase.

  7. Finite-Temperature Crossover Phenomenon in the S = 1/2 Antiferromagnetic Heisenberg Model on the Kagome Lattice

    Science.gov (United States)

    Shimokawa, Tokuro; Kawamura, Hikaru

    2016-11-01

    Thermal properties of the S = 1/2 kagome Heisenberg antiferromagnet at low temperatures are investigated by means of the Hams-de Raedt method for clusters of up to 36 sites possessing a full symmetry of the lattice. The specific heat exhibits, in addition to the double peaks, the third and the fourth peaks at lower temperatures. With decreasing the temperature, the type of the magnetic short-range order (SRO) changes around the third-peak temperature from the √{3} × √{3} to the q = 0 states, suggesting that the third peak of the specific heat is associated with a crossover phenomenon between the spin-liquid states with distinct magnetic SRO. Experimental implications are discussed.

  8. Annealed Ising model with site dilution on self-similar structures

    Science.gov (United States)

    Silva, V. S. T.; Andrade, R. F. S.; Salinas, S. R.

    2014-11-01

    We consider an Ising model on the triangular Apollonian network (AN), with a thermalized distribution of vacant sites. The statistical problem is formulated in a grand canonical ensemble, in terms of the temperature T and a chemical potential μ associated with the concentration of active magnetic sites. We use a well-known transfer-matrix method, with a number of adaptations, to write recursion relations between successive generations of this hierarchical structure. We also investigate the analogous model on the diamond hierarchical lattice (DHL). From the numerical analysis of the recursion relations, we obtain various thermodynamic quantities. In the μ →∞ limit, we reproduce the results for the uniform models: in the AN, the system is magnetically ordered at all temperatures, while in the DHL there is a ferromagnetic-paramagnetic transition at a finite value of T . Magnetic ordering, however, is shown to disappear for sufficiently large negative values of the chemical potential.

  9. Ising-like agent-based technology diffusion model: adoption patterns vs. seeding strategies

    CERN Document Server

    Laciana, Carlos E

    2010-01-01

    The well-known Ising model used in statistical physics was adapted to a social dynamics context to simulate the adoption of a technological innovation. The model explicitly combines (a) an individual's perception of the advantages of an innovation and (b) social influence from members of the decision-maker's social network. The micro-level adoption dynamics are embedded into an agent-based model that allows exploration of macro-level patterns of technology diffusion throughout systems with different configurations (number and distributions of early adopters, social network topologies). In the present work we carry out many numerical simulations. We find that when the gap between the individual's perception of the options is high, the adoption speed increases if the dispersion of early adopters grows. Another test was based on changing the network topology by means of stochastic connections to a common opinion reference (hub), which resulted in an increment in the adoption speed. Finally, we performed a simula...

  10. Non-Markovian Persistence at the PC point of a 1d non-equilibrium kinetic Ising model

    CERN Document Server

    Menyhard, N; Menyhard, Nora; Odor, Geza

    1997-01-01

    One-dimensional non-equilibrium kinetic Ising models evolving under the competing effect of spin flips at zero temperature and nearest neighbour spin exchanges exhibiting a parity-conserving (PC) phase transition on the level of kinks are investigated here numerically from the point of view of the underlying spin system. The dynamical persistency exponent $\\Theta$ and the exponent $lambda$ characterising the two-time autocorrelation function of the total magnetization under non-equilibrium conditions are reported. It is found that the PC transition has strong effect: the process becomes non-Markovian and the above exponents exhibit drastic changes as compared to the Glauber-Ising case.

  11. Spin-3/2 Ising model AFM/AFM two-layer lattice with crystal field

    Institute of Scientific and Technical Information of China (English)

    Erhan Albayrak; Ali Yigit

    2009-01-01

    The spin-3/2 Ising model is investigated for the case of antiferromagnetic (AFM/AFM) interactions on the two-layer Bethe lattice by using the exact recursion relations in the pairwise approach for given coordination numbers q = 3, 4 and 6 when the layers are under the influences of equal external magnetic and equal crystal fields. The ground state, (GS) phase diagrams are obtained on the different planes in detail and then the temperature-dependent phase diagrams of the system are calculated accordingly. It is observed that the system presents both second- and first-order phase transitions for all q, therefore, tricritical points. It is also found that the system exhibits double-critical end points and isolated points. The model aiso presents two Néel temperatures, T_N, and the existence of which leads to the reentrant behaviour.

  12. Mixed spin Ising model with four-spin interaction and random crystal field

    Energy Technology Data Exchange (ETDEWEB)

    Benayad, N., E-mail: n.benayad@fsac.ac.ma [Groupe de Mecanique Statistique, Laboratoire de physique theorique et appliquee, Faculte des sciences-Aien Chock, Universite Hassan II-Casablanca, B.P 5366 Maarif, Casablanca 20100 (Morocco); Laboratoire de physique des hautes energies et de la matiere condensee, Faculte des sciences-Aien Chock, Universite Hassan II-Casablanca, B.P 5366 Maarif, Casablanca 20100 (Morocco); Ghliyem, M. [Groupe de Mecanique Statistique, Laboratoire de physique theorique et appliquee, Faculte des sciences-Aien Chock, Universite Hassan II-Casablanca, B.P 5366 Maarif, Casablanca 20100 (Morocco); Laboratoire de physique des hautes energies et de la matiere condensee, Faculte des sciences-Aien Chock, Universite Hassan II-Casablanca, B.P 5366 Maarif, Casablanca 20100 (Morocco)

    2012-01-01

    The effects of fluctuations of the crystal field on the phase diagram of the mixed spin-1/2 and spin-1 Ising model with four-spin interactions are investigated within the finite cluster approximation based on a single-site cluster theory. The state equations are derived for the two-dimensional square lattice. It has been found that the system exhibits a variety of interesting features resulting from the fluctuation of the crystal field interactions. In particular, for low mean value D of the crystal field, the critical temperature is not very sensitive to fluctuations and all transitions are of second order for any value of the four-spin interactions. But for relatively high D, the transition temperature depends on the fluctuation of the crystal field, and the system undergoes tricritical behaviour for any strength of the four-spin interactions. We have also found that the model may exhibit reentrance for appropriate values of the system parameters.

  13. Entanglement and quantum phase transition in the Heisenberg-Ising model

    Institute of Scientific and Technical Information of China (English)

    Tan Xiao-Dong; Jin Bai-Qi; Gao Wei

    2013-01-01

    We use the quantum renormalization-group (QRG) method to study the entanglement and quantum phase transition (QPT) in the one-dimensional spin-l/2 Heisenberg-Ising model [Lieb E,Schultz T and Mattis D 1961 Ann.Phys.(N.Y.)16 407].We find the quantum phase boundary of this model by investigating the evolution of concurrence in terms of QRG iterations.We also investigate the scaling behavior of the system close to the quantum critical point,which shows that the minimum value of the first derivative of concurrence and the position of the minimum scale with an exponent of the system size.Also,the first derivative of concurrence between two blocks diverges at the quantum critical point,which is directly associated with the divergence of the correlation length.

  14. The square lattice Ising model on the rectangle I: Finite systems

    CERN Document Server

    Hucht, Alfred

    2016-01-01

    The partition function of the square lattice Ising model on the rectangle is calculated exactly for arbitrary system size $L\\times M$ and temperature. We start with the dimer method of Kasteleyn, McCoy & Wu, construct a highly symmetric block transfer matrix and derive a factorization of the involved determinant, effectively decomposing the free energy into two parts, $F(L,M)=F_{\\infty}^{\\leftrightarrow}(L,M)+F_\\mathrm{res}^{\\leftrightarrow}(L,M)$. The residual part $F_\\mathrm{res}^{\\leftrightarrow}(L,M)$ contains the nontrivial finite-size contributions and becomes exponentially small for large $L/M$ and off-critical temperatures. It is given by the determinant of a $\\frac{M}{2}\\times\\frac{M}{2}$ matrix and can be mapped onto an effective spin model with $M$ spins and long-range interactions. The relations to the Casimir potential and the Casimir force scaling functions are discussed.

  15. Quantum Phase Transition in the Two-Dimensional Random Transverse-Field Ising Model

    Science.gov (United States)

    Pich, C.; Young, A. P.

    1998-03-01

    We study the quantum phase transition in the random transverse-field Ising model by Monte Carlo simulations. In one-dimension it has been established that this system has the following striking behavior: (i) the dynamical exponent is infinite, and (ii) the exponents for the divergence of the average and typical correlation lengths are different. An important issue is whether this behavior is special to one-dimension or whether similar behavior persists in higher dimensions. Here we attempt to answer this question by studies of the two-dimensional model. Our simulations use the Wolff cluster algorithm and the results are analyzed by anisotropic finite size scaling, paying particular attention to the Binder ratio of moments of the order parameter distribution and the distribution of the spin-spin correlation functions for various distances.

  16. Universal Finite Size Corrections and the Central Charge in Non-solvable Ising Models

    Science.gov (United States)

    Giuliani, Alessandro; Mastropietro, Vieri

    2013-11-01

    We investigate a non-solvable two-dimensional ferromagnetic Ising model with nearest neighbor plus weak finite range interactions of strength λ. We rigorously establish one of the predictions of Conformal Field Theory (CFT), namely the fact that at the critical temperature the finite size corrections to the free energy are universal, in the sense that they are exactly independent of the interaction. The corresponding central charge, defined in terms of the coefficient of the first subleading term to the free energy, as proposed by Affleck and Blote-Cardy-Nightingale, is constant and equal to 1/2 for all and λ 0 a small but finite convergence radius. This is one of the very few cases where the predictions of CFT can be rigorously verified starting from a microscopic non solvable statistical model. The proof uses a combination of rigorous renormalization group methods with a novel partition function inequality, valid for ferromagnetic interactions.

  17. The bulk, surface and corner free energies of the square lattice Ising model

    Science.gov (United States)

    Baxter, R. J.

    2017-01-01

    We use Kaufman’s spinor method to calculate the bulk, surface and corner free energies {f}{{b}},{f}{{s}},{f}{{s}}\\prime ,{f}{{c}} of the anisotropic square lattice zero-field Ising model for the ordered ferromagnetic case. For {f}{{b}},{f}{{s}},{f}{{s}}\\prime our results of course agree with the early work of Onsager, McCoy and Wu. We also find agreement with the conjectures made by Vernier and Jacobsen (VJ) for the isotropic case. We note that the corner free energy f c depends only on the elliptic modulus k that enters the working, and not on the argument v, which means that VJ’s conjecture applies for the full anisotropic model. The only aspect of this paper that is new is the actual derivation of f c, but by reporting all four free energies together we can see interesting structures linking them.

  18. Hierarchy of correlations for the Ising model in the Majorana representation

    Science.gov (United States)

    Gómez-León, Álvaro

    2017-08-01

    We study the quantum Ising model in D dimensions with the equation-of-motion technique and the Majorana representation for spins. The decoupling scheme used for the Green's functions is based on the hierarchy of correlations in position space. To lowest order, this method reproduces the well-known mean field phase diagram and critical exponents. When correlations between spins are included, we show how the appearance of thermal fluctuations and magnons strongly affects the physical properties. In one dimension and for B =0 we demonstrate that, to first order in correlations, thermal fluctuations completely destroy the ordered phase. For nonvanishing transverse field we show that the model exhibits different behavior than its classical counterpart, especially near the quantum critical point. We discuss the connection with the Dyson's equation formalism and the explicit form of the self-energies.

  19. Properties of the ground state in a spin-2 transverse Ising model with the presence of a crystal field

    Institute of Scientific and Technical Information of China (English)

    姜伟; 魏国柱; 杜安; 张起

    2002-01-01

    The properties of the ground state in the spin-2 transverse Ising model with the presence of a crystal field arestudied by using the effective-field theory with correlations. The longitudinal and transverse magnetizations, the phasediagram and the internal energy in the ground state are given numerically for a honeycomb lattice (z=3).

  20. Properties of the ground state in a spin—2 transverse Ising model with the presence of a srystal field

    Institute of Scientific and Technical Information of China (English)

    姜伟; 魏国柱; 等

    2002-01-01

    The properties of the ground state in the spin-2 transverse Ising model with the presence of a crystal of a crystal field are studied by using the effective-field theory with correlations,The longitudinal and transverse magnetizations,the phase diagram and the internal energy in the ground state are given numerically for a honeycomb lattice(z=3).

  1. Modal analysis of kagome-lattice structures

    Science.gov (United States)

    Perez, H.; Blakley, S.; Zheltikov, A. M.

    2015-05-01

    The first few lowest order circularly symmetric electromagnetic eigenmodes of a full kagome lattice are compared to those of a kagome lattice with a hexagonal defect. This analysis offers important insights into the physics behind the waveguiding properties of hollow-core fibers with a kagome-lattice cladding.

  2. Reentrant transitions of a mixed-spin Ising model on the diced lattice

    Directory of Open Access Journals (Sweden)

    M.Jascur

    2005-01-01

    Full Text Available Magnetic behaviour of a mixed spin-1/2 and spin-1 Ising model on the diced lattice is studied using an exact star-triangle mapping transformation. It is found that the uniaxial as well as biaxial single-ion anisotropy acting on the spin-1 sites may potentially cause a reentrant transition with two consecutive critical points. Contrary to this, the effect of next-nearest-neighbour interaction between the spin-1/2 sites possibly leads to a reentrant transition with three critical temperatures in addition to the one with two critical points only. The shape of the total magnetization versus temperature dependence is particularly investigated for the case of ferrimagnetically ordered system.

  3. Effective-Field Theory for Kinetic Ising Model on Honeycomb Lattice

    Institute of Scientific and Technical Information of China (English)

    SHI Xiao-Ling; WEI Guo-Zhu

    2009-01-01

    As an analytical method, the effective-field theory (EFT) is used to study the dynamical response of the kinetic Ising model in the presence of a sinusoidal oscillating field. The effective-field equations of motion of the average magnetization are given for the honeycomb lattice (Z = 3). The Liapunov exponent A is calculated for discussing the stability of the magnetization and it is used to determine the phase boundary. In the field amplitude ho / Z J-temperature T/ Z J plane, the phase boundary separating the dynamic ordered and the disordered phase has been drawn. In contrast to previous analytical results that predicted a tricritical point separating a dynamic phase boundary line of continuous and discontinuous transitions, we find that the transition is always continuous. There is inconsistency between our results and previous analytical restdts, because they do not introduce sufficiently strong fluctuations.

  4. Non-equilibrium steady states in two-temperature Ising models with Kawasaki dynamics

    Science.gov (United States)

    Borchers, Nick; Pleimling, Michel; Zia, R. K. P.

    2013-03-01

    From complex biological systems to a simple simmering pot, thermodynamic systems held out of equilibrium are exceedingly common in nature. Despite this, a general theory to describe these types of phenomena remains elusive. In this talk, we explore a simple modification of the venerable Ising model in hopes of shedding some light on these issues. In both one and two dimensions, systems attached to two distinct heat reservoirs exhibit many of the hallmarks of phase transition. When such systems settle into a non-equilibrium steady-state they exhibit numerous interesting phenomena, including an unexpected ``freezing by heating.'' There are striking and surprising similarities between the behavior of these systems in one and two dimensions, but also intriguing differences. These phenomena will be explored and possible approaches to understanding the behavior will be suggested. Supported by the US National Science Foundation through Grants DMR-0904999, DMR-1205309, and DMR-1244666

  5. Magnetic Quantum Phase Transitions of a Kondo Lattice Model with Ising Anisotropy

    Science.gov (United States)

    Zhu, Jian-Xin; Kirchner, Stefan; Si, Qimiao; Grempel, Daniel R.; Bulla, Ralf

    2006-03-01

    We study the Kondo Lattice model with Ising anisotropy, within an extended dynamical mean field theory (EDMFT) in the presence or absence of antiferromagnetic ordering. The EDMFT equations are studied using both the Quantum Monte Carlo (QMC) and Numerical Renormalization Group (NRG) methods. We discuss the overall magnetic phase diagram by studying the evolution, as a function of the ratio of the RKKY interaction and bare Kondo scale, of the local spin susceptibility, magnetic order parameter, and the effective Curie constant of a nominally paramagnetic solution with a finite moment. We show that, within the numerical accuracy, the quantum magnetic transition is second order. The local quantum critical aspect of the transition is also discussed.

  6. Motif based hierarchical random graphs: structural properties and critical points of an Ising model

    CERN Document Server

    Kotorowicz, M; 10.5488/CMP.14.13801

    2011-01-01

    A class of random graphs is introduced and studied. The graphs are constructed in an algorithmic way from five motifs which were found in [Milo R., Shen-Orr S., Itzkovitz S., Kashtan N., Chklovskii D., Alon U., Science, 2002, 298, 824-827]. The construction scheme resembles that used in [Hinczewski M., A. Nihat Berker, Phys. Rev. E, 2006, 73, 066126], according to which the short-range bonds are non-random, whereas the long-range bonds appear independently with the same probability. A number of structural properties of the graphs have been described, among which there are degree distributions, clustering, amenability, small-world property. For one of the motifs, the critical point of the Ising model defined on the corresponding graph has been studied.

  7. Estimates of critical quantities from an expansion in mass: Ising model on the simple cubic lattice

    CERN Document Server

    Yamada, Hirofumi

    2015-01-01

    In Ising model on the simple cubic lattice, we describe the inverse temperature $\\beta$ and other quantities relevant for the computation of critical quantities in terms of a dimensionless squared mass $M$. The critical behaviors of those quantities are represented by the linear differential equations with constant coefficients which are related to critical exponents. We estimate the critical temperature and exponents via an expansion in the inverse powers of the mass under the use of $\\delta$-expansion. The critical inverse temperature $\\beta_{c}$ is estimated first in unbiased manner and then critical exponents are also estimated in biased and unbiased self-contained way including $\\omega$, the correction-to-scaling exponent, $\

  8. Partition and Correlation Functions of a Freely Crossed Network Using Ising Model-Type Interactions

    CERN Document Server

    Saito, Akira

    2016-01-01

    We set out to determine the partition and correlation functions of a network under the assumption that its elements are freely connected, with an Ising model-type interaction energy associated with each connection. The partition function is obtained from all combinations of loops on the free network, while the correlation function between two elements is obtained based on all combinations of routes between these points, as well as all loops on the network. These functions allow measurement of the dynamics over the whole of any network, regardless of its form. Furthermore, even as parts are added to the network, the partition and correlation functions can still be obtained. As an example, we obtain the partition and correlation functions in a crystal system under the repeated addition of fixed parts.

  9. High-Temperature Cutoff Approximation of the 3D Kinetic Ising Model

    Institute of Scientific and Technical Information of China (English)

    ZHU JianYang; YANG ZhanRu

    2001-01-01

    A single-spin transition critical dynamics is used to investigate the three-dimensional kinetic Ising model on an anisotropic cubic lattice. We first derive the fundamental dynamical equations, and then linearize them by a cutoff approximation. We obtain the approximate solutions of the local magnetization and equal-time pair correlation function in zero field. In which the axial-decoupling terms γ1γ2, γ2γ3 and γ1γ3 as higher infinitesimal quantity are ignored, where γa = tanh(2kα) = tanh(2Jα/kβT) (α = 1,2,3). We think that it is reasonable as the temperature of the system is very high. The result of what we obtain in this paper can go back to the one-dimensional Glauber's theory as long as k2 = k3= 0.

  10. The cellular Ising model: a framework for phase transitions in multicellular environments.

    Science.gov (United States)

    Weber, Marc; Buceta, Javier

    2016-06-01

    Inspired by the Ising model, we introduce a gene regulatory network that induces a phase transition that coordinates robustly the behaviour of cell ensembles. The building blocks of the design are the so-called toggle switch interfaced with two quorum sensing modules, Las and Lux. We show that as a function of the transport rate of signalling molecules across the cell membrane the population undergoes a spontaneous symmetry breaking from cells individually switching their phenotypes to a global collective phenotypic organization. By characterizing the critical behaviour, we reveal some properties, such as phenotypic memory and hypersensitivity, with relevance in the field of synthetic biology. We argue that our results can be extrapolated to other multicellular systems and be a generic framework for collective decision-making processes. © 2016 The Author(s).

  11. Depinning transition and thermal fluctuations in the random-field Ising model.

    Science.gov (United States)

    Roters, L; Hucht, A; Lübeck, S; Nowak, U; Usadel, K D

    1999-11-01

    We analyze the depinning transition of a driven interface in the three-dimensional (3D) random field Ising model (RFIM) with quenched disorder by means of Monte Carlo simulations. The interface initially built into the system is perpendicular to the [111] direction of a simple cubic lattice. We introduce an algorithm which is capable of simulating such an interface independent of the considered dimension and time scale. This algorithm is applied to the 3D RFIM to study both the depinning transition and the influence of thermal fluctuations on this transition. It turns out that in the RFIM characteristics of the depinning transition depend crucially on the existence of overhangs. Our analysis yields critical exponents of the interface velocity, the correlation length, and the thermal rounding of the transition. We find numerical evidence for a scaling relation for these exponents and the dimension d of the system.

  12. Properties of Interfaces in the two and three dimensional Ising Model

    CERN Document Server

    Berg, B A; Neuhaus, T; 10.1007/BF02198159

    2009-01-01

    To investigate order-order interfaces, we perform multimagnetical Monte Carlo simulations of the $2D$ and $3D$ Ising model. Following Binder we extract the interfacial free energy from the infinite volume limit of the magnetic probability density. Stringent tests of the numerical methods are performed by reproducing with high precision exact $2D$ results. In the physically more interesting $3D$ case we estimate the amplitude $F^s_0$ of the critical interfacial tension $F^s = F^s_0 t^\\mu$ to be $F^s_0 = 1.52 \\pm 0.05$. This result is in good agreement with a previous MC calculation by Mon, as well as with experimental results for related amplitude ratios. In addition, we study in some details the shape of the magnetic probability density for temperatures below the Curie point.

  13. Spin-Polarization of Ferroelectric Supperlattice with Spin-1/2 Transverse Ising Model

    Institute of Scientific and Technical Information of China (English)

    WANG Chun-Dong; TENG Bao-Hua; LU Zhen-Zhen; KWOK So-Ying

    2011-01-01

    By using the simple decoupling approximation to Fermi-type Green's function for the transverse Ising model under pseudospin theory, we systemically study the influence of different exchange interactions (transverse fields) of the two distinct materials on the polarization and Curie temperature of finite alternating superlattice. Meanwhile,we analyze the effect of the whole parameters of the top surface, present their influence on the polarization of each layer (including the mean polarization of the whole ferroelectric superlattice) and on the Curie temperature. The results show the ratio of the exchange interactions (the transverse fields), which are of the two alternating materials have deeply impact on the polarization and Curie temperature of the supperlattice. Moreover, the top surface also has great influence on the whole ferroelectric superlattice.

  14. Monte Carlo analysis of critical phenomenon of the Ising model on memory stabilizer structures

    Science.gov (United States)

    Viteri, C. Ricardo; Tomita, Yu; Brown, Kenneth R.

    2009-10-01

    We calculate the critical temperature of the Ising model on a set of graphs representing a concatenated three-bit error-correction code. The graphs are derived from the stabilizer formalism used in quantum error correction. The stabilizer for a subspace is defined as the group of Pauli operators whose eigenvalues are +1 on the subspace. The group can be generated by a subset of operators in the stabilizer, and the choice of generators determines the structure of the graph. The Wolff algorithm, together with the histogram method and finite-size scaling, is used to calculate both the critical temperature and the critical exponents of each structure. The simulations show that the choice of stabilizer generators, both the number and the geometry, has a large effect on the critical temperature.

  15. Monte Carlo analysis of critical phenomenon of the Ising model on memory stabilizer structures

    CERN Document Server

    Viteri, C Ricardo; Brown, Kenneth R

    2009-01-01

    We calculate the critical temperature of the Ising model on a set of graphs representing a concatenated three-bit error-correction code. The graphs are derived from the stabilizer formalism used in quantum error correction. The stabilizer for a subspace is defined as the group of Pauli operators whose eigenvalues are +1 on the subspace. The group can be generated by a subset of operators in the stabilizer, and the choice of generators determines the structure of the graph. The Wolff algorithm, together with the histogram method and finite-size scaling, is used to calculate both the critical temperature and the critical exponents of each structure. The simulations show that the choice of stabilizer generators, both the number and the geometry, has a large effect on the critical temperature.

  16. Quantum phase transition of the transverse-field quantum Ising model on scale-free networks.

    Science.gov (United States)

    Yi, Hangmo

    2015-01-01

    I investigate the quantum phase transition of the transverse-field quantum Ising model in which nearest neighbors are defined according to the connectivity of scale-free networks. Using a continuous-time quantum Monte Carlo simulation method and the finite-size scaling analysis, I identify the quantum critical point and study its scaling characteristics. For the degree exponent λ=6, I obtain results that are consistent with the mean-field theory. For λ=4.5 and 4, however, the results suggest that the quantum critical point belongs to a non-mean-field universality class. Further simulations indicate that the quantum critical point remains mean-field-like if λ>5, but it continuously deviates from the mean-field theory as λ becomes smaller.

  17. Behavior of Early Warnings near the Critical Temperature in the Two-Dimensional Ising Model

    Science.gov (United States)

    Morales, Irving O.; Landa, Emmanuel; Angeles, Carlos Calderon; Toledo, Juan C.; Rivera, Ana Leonor; Temis, Joel Mendoza; Frank, Alejandro

    2015-01-01

    Among the properties that are common to complex systems, the presence of critical thresholds in the dynamics of the system is one of the most important. Recently, there has been interest in the universalities that occur in the behavior of systems near critical points. These universal properties make it possible to estimate how far a system is from a critical threshold. Several early-warning signals have been reported in time series representing systems near catastrophic shifts. The proper understanding of these early-warnings may allow the prediction and perhaps control of these dramatic shifts in a wide variety of systems. In this paper we analyze this universal behavior for a system that is a paradigm of phase transitions, the Ising model. We study the behavior of the early-warning signals and the way the temporal correlations of the system increase when the system is near the critical point. PMID:26103513

  18. Quantum phase transition of the transverse-field quantum Ising model on scale-free networks

    Science.gov (United States)

    Yi, Hangmo

    2015-01-01

    I investigate the quantum phase transition of the transverse-field quantum Ising model in which nearest neighbors are defined according to the connectivity of scale-free networks. Using a continuous-time quantum Monte Carlo simulation method and the finite-size scaling analysis, I identify the quantum critical point and study its scaling characteristics. For the degree exponent λ =6 , I obtain results that are consistent with the mean-field theory. For λ =4.5 and 4, however, the results suggest that the quantum critical point belongs to a non-mean-field universality class. Further simulations indicate that the quantum critical point remains mean-field-like if λ >5 , but it continuously deviates from the mean-field theory as λ becomes smaller.

  19. Rhythmic behavior in a two-population mean field Ising model

    CERN Document Server

    Collet, Francesca; Tovazzi, Daniele

    2016-01-01

    Many real systems comprised of a large number of interacting components, as for instance neural networks , may exhibit collective periodic behavior even though single components have no natural tendency to behave periodically. Macroscopic oscillations are indeed one of the most common self-organized behavior observed in living systems. In the present paper we study some dynamical features of a two-population generalization of the mean field Ising model with the scope of investigating simple mechanisms capable to generate rhythm in large groups of interacting individuals. We show that the system may undergo a transition from a disordered phase, where the magnetization of each population fluctuates closely around zero, to a phase in which they both display a macroscopic regular rhythm. In particular, there exists a region in the parameter space where having two groups of spins with inter- and intra-population interactions of different strengths suffices for the emergence of a robust periodic behavior.

  20. FPGA Hardware Acceleration of Monte Carlo Simulations for the Ising Model

    CERN Document Server

    Ortega-Zamorano, Francisco; Cannas, Sergio A; Jerez, José M; Franco, Leonardo

    2016-01-01

    A two-dimensional Ising model with nearest-neighbors ferromagnetic interactions is implemented in a Field Programmable Gate Array (FPGA) board.Extensive Monte Carlo simulations were carried out using an efficient hardware representation of individual spins and a combined global-local LFSR random number generator. Consistent results regarding the descriptive properties of magnetic systems, like energy, magnetization and susceptibility are obtained while a speed-up factor of approximately 6 times is achieved in comparison to previous FPGA-based published works and almost $10^4$ times in comparison to a standard CPU simulation. A detailed description of the logic design used is given together with a careful analysis of the quality of the random number generator used. The obtained results confirm the potential of FPGAs for analyzing the statistical mechanics of magnetic systems.

  1. Rhythmic behavior in a two-population mean-field Ising model

    Science.gov (United States)

    Collet, Francesca; Formentin, Marco; Tovazzi, Daniele

    2016-10-01

    Many real systems composed of a large number of interacting components, as, for instance, neural networks, may exhibit collective periodic behavior even though single components have no natural tendency to behave periodically. Macroscopic oscillations are indeed one of the most common self-organized behavior observed in living systems. In the present paper we study some dynamical features of a two-population generalization of the mean-field Ising model with the scope of investigating simple mechanisms capable to generate rhythms in large groups of interacting individuals. We show that the system may undergo a transition from a disordered phase, where the magnetization of each population fluctuates closely around zero, to a phase in which they both display a macroscopic regular rhythm. In particular, there exists a region in the parameter space where having two groups of spins with inter- and intrapopulation interactions of different strengths suffices for the emergence of a robust periodic behavior.

  2. OPE Coefficients of the 3D Ising model with a trapping potential

    CERN Document Server

    Costagliola, Gianluca

    2015-01-01

    Recently the OPE coefficients of the 3D Ising model universality class have been calculated by studying the two-point functions perturbed from the critical point with a relevant field. We show that this method can be applied also when the perturbation is performed with a relevant field coupled to a non uniform potential acting as a trap. This setting is described by the trap size scaling ansatz, that can be combined with the general framework of the conformal perturbation in order to write down the correlators $$, $$ and $$, from which the OPE coefficients can be estimated. We find $C^{\\sigma}_{\\sigma\\epsilon}= 1.051(3)$ , in agreement with the results already known in the literature, and $C^{\\epsilon}_{\\epsilon\\epsilon}= 1.32 (15)$ , confirming and improving the previous estimate obtained in the uniform perturbation case.

  3. The scaling window of the 5D Ising model with free boundary conditions

    Science.gov (United States)

    Lundow, P. H.; Markström, K.

    2016-10-01

    The five-dimensional Ising model with free boundary conditions has recently received a renewed interest in a debate concerning the finite-size scaling of the susceptibility near the critical temperature. We provide evidence in favour of the conventional scaling picture, where the susceptibility scales as L2 inside a critical scaling window of width 1 /L2. Our results are based on Monte Carlo data gathered on system sizes up to L = 79 (ca. three billion spins) for a wide range of temperatures near the critical point. We analyse the magnetisation distribution, the susceptibility and also the scaling and distribution of the size of the Fortuin-Kasteleyn cluster containing the origin. The probability of this cluster reaching the boundary determines the correlation length, and its behaviour agrees with the mean field critical exponent δ = 3, that the scaling window has width 1 /L2.

  4. Form factor expansions in the 2D Ising model and Painleve VI

    Energy Technology Data Exchange (ETDEWEB)

    Mangazeev, Vladimir V., E-mail: Vladimir.Mangazeev@anu.edu.a [Department of Theoretical Physics, Research School of Physics and Engineering, Australian National University, Canberra, ACT 0200 (Australia); Guttmann, Anthony J., E-mail: tonyg@ms.unimelb.edu.a [ARC Centre of Excellence for Mathematics and Statistics of Complex Systems, Department of Mathematics and Statistics, The University of Melbourne, Victoria 3010 (Australia)

    2010-10-21

    We derive a Toda-type recurrence relation, in both high- and low-temperature regimes, for the {lambda}-extended diagonal correlation functions C(N,N;{lambda}) of the two-dimensional Ising model, using an earlier connection between diagonal form factor expansions and tau-functions within Painleve VI (PVI) theory, originally discovered by Jimbo and Miwa. This greatly simplifies the calculation of the diagonal correlation functions, particularly their {lambda}-extended counterparts. We also conjecture a closed form expression for the simplest off-diagonal case C{sup {+-}}(0,1;{lambda}) where a connection to PVI theory is not known. Combined with the results for diagonal correlations these give all the initial conditions required for the {lambda}-extended version of quadratic difference equations for the correlation functions discovered by McCoy, Perk and Wu. The results obtained here should provide a further potential algorithmic improvement in the {lambda}-extended case, and facilitate other developments.

  5. Applicability of n-vicinity method for calculation of free energy of Ising model

    Science.gov (United States)

    Kryzhanovsky, Boris; Litinskii, Leonid

    2017-02-01

    Here we apply the n-vicinity method of approximate calculation of the partition function to an Ising Model with the nearest neighbor interaction on D-dimensional hypercube lattice. We solve the equation of state for an arbitrary dimension D and analyze the behavior of the free energy. As expected, for large dimensions (D ≥ 3) the system demonstrates a phase transition of the second kind. In this case, we obtain a simple analytical expression for the critical value of the inverse temperature. When 3 ≤ D ≤ 7 this expression is in a very good agreement with the results of computer simulations. In the case of small dimensions (D = 1 , 2), there is a noticeable discrepancy with the known exact results.

  6. Correlation functions of the one-dimensional random field Ising model at zero temperature

    CERN Document Server

    Farhi, E; Farhi, Edward; Gutmann, Sam

    1993-01-01

    We consider the one-dimensional random field Ising model, where the spin-spin coupling, $J$, is ferromagnetic and the external field is chosen to be $+h$ with probability $p$ and $-h$ with probability $1-p$. At zero temperature, we calculate an exact expression for the correlation length of the quenched average of the correlation function $\\langle s_0 s_n \\rangle - \\langle s_0 \\rangle \\langle s_n \\rangle$ in the case that $2J/h$ is not an integer. The result is a discontinuous function of $2J/h$. When $p = {1 \\over 2}$, we also place a bound on the correlation length of the quenched average of the correlation function $\\langle s_0 s_n \\rangle$.

  7. Behavior of Early Warnings near the Critical Temperature in the Two-Dimensional Ising Model.

    Directory of Open Access Journals (Sweden)

    Irving O Morales

    Full Text Available Among the properties that are common to complex systems, the presence of critical thresholds in the dynamics of the system is one of the most important. Recently, there has been interest in the universalities that occur in the behavior of systems near critical points. These universal properties make it possible to estimate how far a system is from a critical threshold. Several early-warning signals have been reported in time series representing systems near catastrophic shifts. The proper understanding of these early-warnings may allow the prediction and perhaps control of these dramatic shifts in a wide variety of systems. In this paper we analyze this universal behavior for a system that is a paradigm of phase transitions, the Ising model. We study the behavior of the early-warning signals and the way the temporal correlations of the system increase when the system is near the critical point.

  8. A boundary field induced first-order transition in the 2D Ising model: numerical study

    Energy Technology Data Exchange (ETDEWEB)

    Bittner, Elmar; Janke, Wolfhard [Institut fuer Theoretische Physik and Centre for Theoretical Sciences (NTZ), Universitaet Leipzig, Postfach 100 920, D-04009 Leipzig (Germany)], E-mail: elmar.bittner@itp.uni-leipzig.de, E-mail: Wolfhard.janke@itp.uni-leipzig.de

    2008-10-03

    In a recent paper, Clusel and Fortin (2006 J. Phys. A: Math. Gen. 39 995) presented an analytical study of a first-order transition induced by an inhomogeneous boundary magnetic field in the two-dimensional Ising model. They identified the transition that separates the regime where the interface is localized near the boundary from that where it propagates inside the bulk. Inspired by these results, we measured the interface tension by using multimagnetic simulations combined with parallel tempering to determine the phase transition and the location of the interface. Our results are in very good agreement with the theoretical predictions. Furthermore, we studied the spin-spin correlation function for which no analytical results are available.

  9. Critical Casimir force scaling functions of the two-dimensional Ising model for various boundary conditions

    CERN Document Server

    Hobrecht, Hendrik

    2016-01-01

    We present a systematic method to calculate the scaling functions for the critical Casimir force and the according potential of the two-dimensional Ising model with various boundary conditions. Therefore we start with the dimer representation of the corresponding partition function $Z$ on an $L\\times M$ square lattice, wrapped around a torus with aspect ratio $\\rho=L/M$. By assuming periodic boundary conditions and translational invariance in at least one direction, we systematically reduce the problem to a $2\\times2$ transfer matrix representation. For the torus we first reproduce the results by Kaufman and then give a detailed calculation of the scaling functions. Afterwards we present the calculation for the cylinder with open boundary conditions. All scaling functions are given in form of combinations of infinite products and integrals. Our results reproduce the known scaling functions in the limit of thin films $\\rho\\to 0$. Additionally, for the cylinder at criticality our result confirms the predictions...

  10. Scaling of geometric phase versus band structure in cluster-Ising models

    Science.gov (United States)

    Nie, Wei; Mei, Feng; Amico, Luigi; Kwek, Leong Chuan

    2017-08-01

    We study the phase diagram of a class of models in which a generalized cluster interaction can be quenched by an Ising exchange interaction and external magnetic field. The various phases are studied through winding numbers. They may be ordinary phases with local order parameters or exotic ones, known as symmetry protected topologically ordered phases. Quantum phase transitions with dynamical critical exponents z =1 or z =2 are found. In particular, the criticality is analyzed through finite-size scaling of the geometric phase accumulated when the spins of the lattice perform an adiabatic precession. With this study, we quantify the scaling behavior of the geometric phase in relation to the topology and low-energy properties of the band structure of the system.

  11. On the two-dimensional dynamical Ising model in the phase coexistence region

    Science.gov (United States)

    Martinelli, F.

    1994-09-01

    We consider a Glauber dynamics reversible with respect to the two-dimensional Ising model in a finite square of side L, in the absence of an external field and at large inverse temperature β. We first consider the gap in the spectrum of the generator of the dynamics in two different cases: with plus and open boundary conditions. We prove that, when the symmetry under global spin flip is broken by the boundary conditions, the gap is much larger than the case in which the symmetry is present. For this latter we compute exactly the asymptotics of -(1/β L) log(gap) as L→∞ and show that it coincides with the surface tension along one of the coordinate axes. As a consequence we are able to study quite precisely the large deviations in time of the magnetization and to obtain an upper bound on the spin-spin time correlation in the infinite-volume plus phase. Our results establish a connection between the dynamical large deviations and those of the equilibrium Gibbs measure studied by Shlosman in the framework of the rigorous description of the Wulff shape for the Ising model. Finally we show that, in the case of open boundary conditions, it is possible to rescale the time with L in such a way that, as L→∞, the finite-dimensional distributions of the time-rescaled magnetization converge to those of a symmetric continuous-time Markov chain on the two-state space {- m *(β), m *(β)}, m *(β) being the spontaneous magnetization. Our methods rely upon a novel combination of techniques for bounding from below the gap of symmetric Markov chains on complicated graphs, developed by Jerrum and Sinclair in their Markov chain approach to hard computational problems, and the idea of introducing "block Glauber dynamics" instead of the standard single-site dynamics, in order to put in evidence more effectively the effect of the boundary conditions in the approach to equilibrium.

  12. The Ising model: from elliptic curves to modular forms and Calabi-Yau equations

    Energy Technology Data Exchange (ETDEWEB)

    Bostan, A [INRIA Paris-Rocquencourt, Domaine de Voluceau, B.P. 105 78153 Le Chesnay Cedex (France); Boukraa, S [LPTHIRM and Departement d' Aeronautique, Universite de Blida, Blida (Algeria); Hassani, S; Zenine, N [Centre de Recherche Nucleaire d' Alger, 2 Bd. Frantz Fanon, BP 399, 16000 Alger (Algeria); Van Hoeij, M [Florida State University, Department of Mathematics, 1017 Academic Way, Tallahassee, FL 32306-4510 (United States); Maillard, J-M [LPTMC, UMR 7600 CNRS, Universite de Paris, Tour 23, 5eme etage, Case 121, 4 Place Jussieu, 75252 Paris Cedex 05 (France); Weil, J-A, E-mail: alin.bostan@inria.fr, E-mail: boukraa@mail.univ-blida.dz, E-mail: hoeij@mail.math.fsu.edu, E-mail: maillard@lptmc.jussieu.fr, E-mail: jacques-arthur.weil@unilim.fr, E-mail: njzenine@yahoo.com [XLIM, Universite de Limoges, 123 Avenue Albert Thomas, 87060 Limoges Cedex (France)

    2011-01-28

    We show that almost all the linear differential operators factors obtained in the analysis of the n-particle contributions of the susceptibility of the Ising model for n {<=} 6 are linear differential operators associated with elliptic curves. Beyond the simplest differential operators factors which are homomorphic to symmetric powers of the second order operator associated with the complete elliptic integral E, the second and third order differential operators Z{sub 2}, F{sub 2}, F{sub 3}, L-tilde {sub 3} can actually be interpreted as modular forms of the elliptic curve of the Ising model. A last order-4 globally nilpotent linear differential operator is not reducible to this elliptic curve, modular form scheme. This operator is shown to actually correspond to a natural generalization of this elliptic curve, modular form scheme, with the emergence of a Calabi-Yau equation, corresponding to a selected {sub 4}F{sub 3} hypergeometric function. This hypergeometric function can also be seen as a Hadamard product of the complete elliptic integral K, with a remarkably simple algebraic pull-back (square root extension), the corresponding Calabi-Yau fourth order differential operator having a symplectic differential Galois group SP(4,C). The mirror maps and higher order Schwarzian ODEs, associated with this Calabi-Yau ODE, present all the nice physical and mathematical ingredients we had with elliptic curves and modular forms, in particular an exact (isogenies) representation of the generators of the renormalization group, extending the modular group SL(2,Z) to a GL(2,Z) symmetry group.

  13. Magnetic phase diagrams of classical triangular and kagome antiferromagnets

    Energy Technology Data Exchange (ETDEWEB)

    Gvozdikova, M V [Department of Physics, Kharkov National University, 61077 Kharkov (Ukraine); Melchy, P-E; Zhitomirsky, M E, E-mail: mike.zhitomirsky@cea.fr [Service de Physique Statistique, Magnetisme et Supraconductivite, UMR-E9001 CEA-INAC/UJF, 17 rue des Martyrs, 38054 Grenoble (France)

    2011-04-27

    We investigate the effect of geometrical frustration on the H-T phase diagrams of the classical Heisenberg antiferromagnets on triangular and kagome lattices. The phase diagrams for the two models are obtained from large-scale Monte Carlo simulations. For the kagome antiferromagnet, thermal fluctuations are unable to lift degeneracy completely and stabilize translationally disordered multipolar phases. We find a substantial difference in the temperature scales of the order by disorder effect related to different degeneracy of the low- and the high-field classical ground states in the kagome antiferromagnet. In the low-field regime, the Kosterlitz-Thouless transition into a spin-nematic phase is produced by unbinding of half-quantum vortices.

  14. Design of a Kagome lattice from soft anisotropic particles.

    Science.gov (United States)

    Fejer, Szilard N; Wales, David J

    2015-09-07

    We present a simple model of triblock Janus particles based on discoidal building blocks, which can form energetically stabilized Kagome structures. We find 'magic number' global minima in small clusters whenever particle numbers are compatible with a perfect Kagome structure, without constraining the accessible three-dimensional configuration space. The preference for planar structures with two bonds per patch among all other possible minima on the landscape is enhanced when sedimentation forces are included. For the building blocks in question, structures containing three bonds per patch become progressively higher in energy compared to Kagome structures as sedimentation forces increase. Rearrangements between competing structures, as well as ring formation mechanisms are characterised and found to be highly cooperative.

  15. Space Group Symmetry Fractionalization in a Chiral Kagome Heisenberg Antiferromagnet.

    Science.gov (United States)

    Zaletel, Michael P; Zhu, Zhenyue; Lu, Yuan-Ming; Vishwanath, Ashvin; White, Steven R

    2016-05-13

    The anyonic excitations of a spin liquid can feature fractional quantum numbers under space group symmetries. Detecting these fractional quantum numbers, which are analogs of the fractional charge of Laughlin quasiparticles, may prove easier than the direct observation of anyonic braiding and statistics. Motivated by the recent numerical discovery of spin-liquid phases in the kagome Heisenberg antiferromagnet, we theoretically predict the pattern of space group symmetry fractionalization in the kagome lattice SO(3)-symmetric chiral spin liquid. We provide a method to detect these fractional quantum numbers in finite-size numerics which is simple to implement in the density matrix renormalization group. Applying these developments to the chiral spin liquid phase of a kagome Heisenberg model, we find perfect agreement between our theoretical prediction and numerical observations.

  16. Magnetic phase diagrams of classical triangular and kagome antiferromagnets.

    Science.gov (United States)

    Gvozdikova, M V; Melchy, P-E; Zhitomirsky, M E

    2011-04-27

    We investigate the effect of geometrical frustration on the H-T phase diagrams of the classical Heisenberg antiferromagnets on triangular and kagome lattices. The phase diagrams for the two models are obtained from large-scale Monte Carlo simulations. For the kagome antiferromagnet, thermal fluctuations are unable to lift degeneracy completely and stabilize translationally disordered multipolar phases. We find a substantial difference in the temperature scales of the order by disorder effect related to different degeneracy of the low- and the high-field classical ground states in the kagome antiferromagnet. In the low-field regime, the Kosterlitz-Thouless transition into a spin-nematic phase is produced by unbinding of half-quantum vortices.

  17. Thermal entanglement of a spin-1/2 Ising-Heisenberg model on a symmetrical diamond chain.

    Science.gov (United States)

    Ananikian, N S; Ananikyan, L N; Chakhmakhchyan, L A; Rojas, Onofre

    2012-06-27

    The entanglement quantum properties of a spin-1/2 Ising-Heisenberg model on a symmetrical diamond chain were analyzed. Due to the separable nature of the Ising-type exchange interactions between neighboring Heisenberg dimers, calculation of the entanglement can be performed exactly for each individual dimer. Pairwise thermal entanglement was studied in terms of the isotropic Ising-Heisenberg model and analytical expressions for the concurrence (as a measure of bipartite entanglement) were obtained. The effects of external magnetic field H and next-nearest neighbor interaction J(m) between nodal Ising sites were considered. The ground state structure and entanglement properties of the system were studied in a wide range of coupling constant values. Various regimes with different values of ground state entanglement were revealed, depending on the relation between competing interaction strengths. Finally, some novel effects, such as the two-peak behavior of concurrence versus temperature and coexistence of phases with different values of magnetic entanglement, were observed.

  18. Corner wetting in the two-dimensional Ising model: Monte Carlo results

    Science.gov (United States)

    Albano, E. V.; DeVirgiliis, A.; Müller, M.; Binder, K.

    2003-01-01

    Square L × L (L = 24-128) Ising lattices with nearest neighbour ferromagnetic exchange are considered using free boundary conditions at which boundary magnetic fields ± h are applied, i.e., at the two boundary rows ending at the lower left corner a field +h acts, while at the two boundary rows ending at the upper right corner a field -h acts. For temperatures T less than the critical temperature Tc of the bulk, this boundary condition leads to the formation of two domains with opposite orientations of the magnetization direction, separated by an interface which for T larger than the filling transition temperature Tf (h) runs from the upper left corner to the lower right corner, while for T interface is localized either close to the lower left corner or close to the upper right corner. Numerous theoretical predictions for the critical behaviour of this 'corner wetting' or 'wedge filling' transition are tested by Monte Carlo simulations. In particular, it is shown that for T = Tf (h) the magnetization profile m(z) in the z-direction normal to the interface is simply linear and the interfacial width scales as w propto L, while for T > Tf (h) it scales as w proptosurd L. The distribution P (ell) of the interface position ell (measured along the z-direction from the corners) decays exponentially for T Tf (h). Furthermore, the Monte Carlo data are compatible with langleellrangle propto (Tf (h) - T)-1 and a finite size scaling of the total magnetization according to M(L, T) = tilde M {(1 - T/Tf (h))nubot L} with nubot = 1. Unlike the findings for critical wetting in the thin film geometry of the Ising model, the Monte Carlo results for corner wetting are in very good agreement with the theoretical predictions.

  19. Is the full susceptibility of the square-lattice Ising model a differentially algebraic function?

    Science.gov (United States)

    Guttmann, A. J.; Jensen, I.; Maillard, J.-M.; Pantone, J.

    2016-12-01

    We study the class of non-holonomic power series with integer coefficients that reduce, modulo primes, or powers of primes, to algebraic functions. In particular we try to determine whether the susceptibility of the square-lattice Ising model belongs to this class, and more broadly whether the susceptibility is a solution of a differentially algebraic equation. Initial results on Tutte's nonlinear ordinary differential equation (ODE) and other simple quadratic nonlinear ODEs suggest that a large set of differentially algebraic power series solutions with integer coefficients might reduce to algebraic functions modulo primes, or powers of primes. Since diagonals of rational functions are well-known to reduce, modulo primes, or powers of primes, to algebraic functions, a large subset of differentially algebraic power series with integer coefficients may be viewed as a natural ‘nonlinear’ generalisation of diagonals of rational functions. Here we give several examples of series with integer coefficients and non-zero radius of convergence that reduce to algebraic functions modulo (almost) every prime (or power of a prime). These examples satisfy differentially algebraic equations with the encoding polynomial occasionally possessing quite high degree (and thus difficult to identify even with long series). These examples shed important light on the very nature of such differentially algebraic series. Additionally, we have extended both the high- and low-temperature Ising square-lattice susceptibility series to 5043 coefficients. We find that even this long series is insufficient to determine whether it reduces to algebraic functions modulo 3, 5, etc. This negative result is in contrast to the comparatively easy confirmation that the corresponding series reduce to algebraic functions modulo powers of 2. Finally we show that even with 5043 terms we are unable to identify an underlying differentially algebraic equation for the susceptibility, ruling out a number of

  20. Long-range Ising model for credit portfolios with heterogeneous credit exposures

    Science.gov (United States)

    Kato, Kensuke

    2016-11-01

    We propose the finite-size long-range Ising model as a model for heterogeneous credit portfolios held by a financial institution in the view of econophysics. The model expresses the heterogeneity of the default probability and the default correlation by dividing a credit portfolio into multiple sectors characterized by credit rating and industry. The model also expresses the heterogeneity of the credit exposure, which is difficult to evaluate analytically, by applying the replica exchange Monte Carlo method to numerically calculate the loss distribution. To analyze the characteristics of the loss distribution for credit portfolios with heterogeneous credit exposures, we apply this model to various credit portfolios and evaluate credit risk. As a result, we show that the tail of the loss distribution calculated by this model has characteristics that are different from the tail of the loss distribution of the standard models used in credit risk modeling. We also show that there is a possibility of different evaluations of credit risk according to the pattern of heterogeneity.

  1. Stable kagome lattices from group IV elements

    Science.gov (United States)

    Leenaerts, O.; Schoeters, B.; Partoens, B.

    2015-03-01

    A thorough investigation of three-dimensional kagome lattices of group IV elements is performed with first-principles calculations. The investigated kagome lattices of silicon and germanium are found to be of similar stability as the recently proposed carbon kagome lattice. Carbon and silicon kagome lattices are both direct-gap semiconductors but they have qualitatively different electronic band structures. While direct optical transitions between the valence and conduction bands are allowed in the carbon case, no such transitions can be observed for silicon. The kagome lattice of germanium exhibits semimetallic behavior but can be transformed into a semiconductor after compression.

  2. Comparative study of an Eden model for the irreversible growth of spins and the equilibrium Ising model

    Energy Technology Data Exchange (ETDEWEB)

    Candia, Julian; Albano, Ezequiel V.

    2001-06-01

    The magnetic Eden model (MEM) [N. Vandewalle and M. Ausloos, Phys. Rev. E >50, R635 (1994)] with ferromagnetic interactions between nearest-neighbor spins is studied in (d+1)-dimensional rectangular geometries for d=1,2. In the MEM, magnetic clusters are grown by adding spins at the boundaries of the clusters. The orientation of the added spins depends on both the energetic interaction with already deposited spins and the temperature, through a Boltzmann factor. A numerical Monte Carlo investigation of the MEM has been performed and the results of the simulations have been analyzed using finite-size scaling arguments. As in the case of the Ising model, the MEM in d=1 is noncritical (only exhibits an ordered phase at T=0). In d=2 the MEM exhibits an order-disorder transition of second order at a finite temperature. Such transition has been characterized in detail and the relevant critical exponents have been determined. These exponents are in agreement (within error bars) with those of the Ising model in two dimensions. Further similarities between both models have been found by evaluating the probability distribution of the order parameter, the magnetization, and the susceptibility. Results obtained by means of extensive computer simulations allow us to put forward a conjecture that establishes a nontrivial correspondence between the MEM for the irreversible growth of spins and the equilibrium Ising model. This conjecture is certainly a theoretical challenge and its confirmation will contribute to the development of a framework for the study of irreversible growth processes.

  3. Linking market interaction intensity of 3D Ising type financial model with market volatility

    Science.gov (United States)

    Fang, Wen; Ke, Jinchuan; Wang, Jun; Feng, Ling

    2016-11-01

    Microscopic interaction models in physics have been used to investigate the complex phenomena of economic systems. The simple interactions involved can lead to complex behaviors and help the understanding of mechanisms in the financial market at a systemic level. This article aims to develop a financial time series model through 3D (three-dimensional) Ising dynamic system which is widely used as an interacting spins model to explain the ferromagnetism in physics. Through Monte Carlo simulations of the financial model and numerical analysis for both the simulation return time series and historical return data of Hushen 300 (HS300) index in Chinese stock market, we show that despite its simplicity, this model displays stylized facts similar to that seen in real financial market. We demonstrate a possible underlying link between volatility fluctuations of real stock market and the change in interaction strengths of market participants in the financial model. In particular, our stochastic interaction strength in our model demonstrates that the real market may be consistently operating near the critical point of the system.

  4. Ising Critical Behavior of Inhomogeneous Curie-Weiss Models and Annealed Random Graphs

    Science.gov (United States)

    Dommers, Sander; Giardinà, Cristian; Giberti, Claudio; van der Hofstad, Remco; Prioriello, Maria Luisa

    2016-11-01

    We study the critical behavior for inhomogeneous versions of the Curie-Weiss model, where the coupling constant {J_{ij}(β)} for the edge {ij} on the complete graph is given by {J_{ij}(β)=β w_iw_j/( {sum_{kin[N]}w_k})}. We call the product form of these couplings the rank-1 inhomogeneous Curie-Weiss model. This model also arises [with inverse temperature {β} replaced by {sinh(β)} ] from the annealed Ising model on the generalized random graph. We assume that the vertex weights {(w_i)_{iin[N]}} are regular, in the sense that their empirical distribution converges and the second moment converges as well. We identify the critical temperatures and exponents for these models, as well as a non-classical limit theorem for the total spin at the critical point. These depend sensitively on the number of finite moments of the weight distribution. When the fourth moment of the weight distribution converges, then the critical behavior is the same as on the (homogeneous) Curie-Weiss model, so that the inhomogeneity is weak. When the fourth moment of the weights converges to infinity, and the weights satisfy an asymptotic power law with exponent {τ} with {τin(3,5)}, then the critical exponents depend sensitively on {τ}. In addition, at criticality, the total spin {S_N} satisfies that {S_N/N^{(τ-2)/(τ-1)}} converges in law to some limiting random variable whose distribution we explicitly characterize.

  5. Multicanonical analysis of the plaquette-only gonihedric Ising model and its dual

    Science.gov (United States)

    Mueller, Marco; Johnston, Desmond A.; Janke, Wolfhard

    2014-11-01

    The three-dimensional purely plaquette gonihedric Ising model and its dual are investigated to resolve inconsistencies in the literature for the values of the inverse transition temperature of the very strong temperature-driven first-order phase transition that is apparent in the system. Multicanonical simulations of this model allow us to measure system configurations that are suppressed by more than 60 orders of magnitude compared to probable states. With the resulting high-precision data, we find excellent agreement with our recently proposed nonstandard finite-size scaling laws for models with a macroscopic degeneracy of the low-temperature phase by challenging the prefactors numerically. We find an overall consistent inverse transition temperature of β∞=0.551334(8) from the simulations of the original model both with periodic and fixed boundary conditions, and the dual model with periodic boundary conditions. For the original model with periodic boundary conditions, we obtain the first reliable estimate of the interface tension σ=0.12037(18), using the statistics of suppressed configurations.

  6. Multicanonical analysis of the plaquette-only gonihedric Ising model and its dual

    Directory of Open Access Journals (Sweden)

    Marco Mueller

    2014-11-01

    Full Text Available The three-dimensional purely plaquette gonihedric Ising model and its dual are investigated to resolve inconsistencies in the literature for the values of the inverse transition temperature of the very strong temperature-driven first-order phase transition that is apparent in the system. Multicanonical simulations of this model allow us to measure system configurations that are suppressed by more than 60 orders of magnitude compared to probable states. With the resulting high-precision data, we find excellent agreement with our recently proposed nonstandard finite-size scaling laws for models with a macroscopic degeneracy of the low-temperature phase by challenging the prefactors numerically. We find an overall consistent inverse transition temperature of β∞=0.551334(8 from the simulations of the original model both with periodic and fixed boundary conditions, and the dual model with periodic boundary conditions. For the original model with periodic boundary conditions, we obtain the first reliable estimate of the interface tension σ=0.12037(18, using the statistics of suppressed configurations.

  7. Multicanonical analysis of the plaquette-only gonihedric Ising model and its dual

    Energy Technology Data Exchange (ETDEWEB)

    Mueller, Marco, E-mail: Marco.Mueller@itp.uni-leipzig.de [Institut für Theoretische Physik, Universität Leipzig, Postfach 100 920, D-04009 Leipzig (Germany); Johnston, Desmond A., E-mail: D.A.Johnston@hw.ac.uk [Department of Mathematics and the Maxwell Institute for Mathematical Sciences, Heriot-Watt University, Riccarton, Edinburgh, EH14 4AS, Scotland (United Kingdom); Janke, Wolfhard, E-mail: Wolfhard.Janke@itp.uni-leipzig.de [Institut für Theoretische Physik, Universität Leipzig, Postfach 100 920, D-04009 Leipzig (Germany)

    2014-11-15

    The three-dimensional purely plaquette gonihedric Ising model and its dual are investigated to resolve inconsistencies in the literature for the values of the inverse transition temperature of the very strong temperature-driven first-order phase transition that is apparent in the system. Multicanonical simulations of this model allow us to measure system configurations that are suppressed by more than 60 orders of magnitude compared to probable states. With the resulting high-precision data, we find excellent agreement with our recently proposed nonstandard finite-size scaling laws for models with a macroscopic degeneracy of the low-temperature phase by challenging the prefactors numerically. We find an overall consistent inverse transition temperature of β{sup ∞}=0.551334(8) from the simulations of the original model both with periodic and fixed boundary conditions, and the dual model with periodic boundary conditions. For the original model with periodic boundary conditions, we obtain the first reliable estimate of the interface tension σ=0.12037(18), using the statistics of suppressed configurations.

  8. A study of the bilayer Bethe lattice for spin-32 Ising model

    Energy Technology Data Exchange (ETDEWEB)

    Albayrak, Erhan [Department of Physics, Erciyes University, 38039 Kayseri (Turkey)]. E-mail: albayrak@erciyes.edu.tr; Yilmaz, Saban [Department of Physics, Erciyes University, 38039 Kayseri (Turkey); Akkaya, Seyma [Department of Physics, Erciyes University, 38039 Kayseri (Turkey)

    2007-03-15

    The spin-32 Ising model on the bilayer Bethe lattice is studied in terms of the exact recursion relations with the intralayer bilinear interactions J{sub 11} and J{sub 22} of the two layers with ferromagnetic coupling and interlayer bilinear interaction J{sub 12} between the layers with ferromagnetic or antiferromagnetic coupling. We first have obtained the ground state configurations of the model on the (J{sub 22}/vertical barJ{sub 11}vertical bar,J{sub 12}/qvertical barJ{sub 11}vertical bar) planes for J{sub 11}<0 and J{sub 11}>0. Then the thermal behaviors of the order-parameters, the total and staggered magnetizations of the two layers and also the spin-spin correlation function between the nearest-neighbor spins of the adjacent layers, are studied to obtain the phase diagrams of the model on the (kT/J{sub 11},J{sub 12}/J{sub 11}) plane for given values of J{sub 22}/J{sub 11} and the coordination number q. As a result, a few types of the critical temperatures of the model are obtained.

  9. A new force-extension formula for stretched macromolecules and polymers based on the Ising model

    Science.gov (United States)

    Chan, Yue; Haverkamp, Richard G.

    2016-12-01

    In this paper, we derive a new force-extension formula for stretched macromolecules and homogeneous polymer matrices. The Ising model arising from paramagnetism is employed, where the magnetic force is replaced by the external force, and the resistance energy is addressed in this model instead of the usual persistent length arising from the freely jointed chain and worm-like chain models. While the force-extension formula reveals the distinctive stretching features for stretched polymers, the resistance energy is found to increase almost linearly with the external force for our two polysaccharides stretching examples with and without ring conformational changes. In particular, a jump in the resistance energy which is caused by a conformational transition is investigated, and the gap between the jump determines the energy barrier between two conformational configurations. Our theoretical model matches well with experimental results undergoing no and single conformational transitions, and a Monte Carlo simulation has also been performed to ensure the correctness of the resistance energy. This technique might also be employed to determine the binding energy from other causes during molecular stretching and provide vital information for further theoretical investigations.

  10. Pair correlations and structure factor of the J1-J2 square lattice Ising model in an external field

    Science.gov (United States)

    Guerrero, Alejandra I.; Stariolo, Daniel A.

    2017-01-01

    We compute the structure factor of the J1-J2 Ising model in an external field on the square lattice within the Cluster Variation Method. We use a four point plaquette approximation, which is the minimal one able to capture phases with broken orientational order in real space, like the recently reported Ising-nematic phase in the model. The analysis of different local maxima in the structure factor allows us to track the different phases and phase transitions against temperature and external field. Although the nematic susceptibility is not directly related to the structure factor, we show that because of the close relationship between the nematic order parameter and the structure factor, the latter shows unambiguous signatures of the presence of a nematic phase, in agreement with results from direct minimization of a variational free energy. The disorder variety of the model is identified and the possibility that the CVM four point approximation be exact on the disorder variety is discussed.

  11. Real-space renormalization group for the transverse-field Ising model in two and three dimensions.

    Science.gov (United States)

    Miyazaki, Ryoji; Nishimori, Hidetoshi; Ortiz, Gerardo

    2011-05-01

    The two- and three-dimensional transverse-field Ising models with ferromagnetic exchange interactions are analyzed by means of the real-space renormalization-group method. The basic strategy is a generalization of a method developed for the one-dimensional case, which exploits the exact invariance of the model under renormalization and is known to give the exact values of the critical point and critical exponent ν. The resulting values of the critical exponent ν in two and three dimensions are in good agreement with those for the classical Ising model in three and four dimensions. To the best of our knowledge, this is the first example in which a real-space renormalization group on (2+1)- and (3+1)-dimensional Bravais lattices yields accurate estimates of the critical exponents.

  12. Spontaneous formation of kagome network and Dirac half-semimetal on a triangular lattice

    Science.gov (United States)

    Akagi, Yutaka; Motome, Yukitoshi

    2015-04-01

    In spin-charge coupled systems, geometrical frustration of underlying lattice structures can give rise to nontrivial magnetic orders and electronic states. Here we explore such a possibility in the Kondo lattice model with classical localized spins on a triangular lattice by using a variational calculation and simulated annealing. We find that the system exhibits a four-sublattice collinear ferrimagnetic phase at 5/8 filling for a large Hund's-rule coupling. In this state, the system spontaneously differentiates into the up-spin kagome network and the isolated down-spin sites, which we call the kagome network formation. In the kagome network state, the system becomes Dirac half-semimetallic: The electronic structure shows a massless Dirac node at the Fermi level, and the Dirac electrons are almost fully spin polarized due to the large Hund's-rule coupling. We also study the effect of off-site Coulomb repulsion in the kagome network phase where the system is effectively regarded as a 1/3-filling spinless fermion system on the kagome lattice. We find that, at the level of the mean-field approximation, a √{3 }×√{3 } -type charge order occurs in the kagome network state, implying the possibility of fractional charge excitations in this triangular lattice system. Moreover, we demonstrate that the kagome network formation with fully polarized Dirac electrons are controllable by an external magnetic field.

  13. Numerical evidence for a chiral spin liquid in the XXZ antiferromagnetic Heisenberg model on the kagome lattice at m =2/3 magnetization

    Science.gov (United States)

    Kumar, Krishna; Changlani, Hitesh J.; Clark, Bryan K.; Fradkin, Eduardo

    2016-10-01

    We perform an exact-diagonalization study of the spin-1/2 XXZ Heisenberg antiferromagnet on the kagome lattice at finite magnetization m =2/3 with an emphasis on the X Y point (Jz=0 ) and in the presence of a small chiral term. Recent analytic work by Kumar et al. [K. Kumar, K. Sun, and E. Fradkin, Phys. Rev. B 90, 174409 (2014), 10.1103/PhysRevB.90.174409] on the same model, using a newly developed flux attachment transformation, predicts a plateau at this value of the magnetization described by a chiral spin liquid (CSL) with a spin Hall conductance of σx y=1/2 . Such a state is topological in nature, has a ground-state degeneracy, and exhibits fractional excitations. We analyze the degeneracy structure in the low-energy manifold, identify the candidate topological states, and use them to compute the modular matrices and Chern numbers, all of which strongly agree with expected theoretical behavior for the σx y=1/2 CSL. In the limit of zero chirality, we find on most (not all) clusters that the topological invariants are still those of a CSL.

  14. Stability conditions for fermionic Ising spin-glass models in the presence of a transverse field

    Science.gov (United States)

    Magalhães, S. G.; Zimmer, F. M.; Morais, C. V.

    2009-06-01

    The stability of a spin-glass (SG) phase is analyzed in detail for a fermionic Ising SG (FISG) model in the presence of a magnetic transverse field Γ. The fermionic path integral formalism, replica method and static approach have been used to obtain the thermodynamic potential within one step replica symmetry breaking ansatz. The replica symmetry (RS) results show that the SG phase is always unstable against the replicon. Moreover, the two other eigenvalues λ± of the Hessian matrix (related to the diagonal elements of the replica matrix) can indicate an additional instability to the SG phase, which enhances when Γ is increased. Therefore, this result suggests that the study of the replicon cannot be enough to guarantee the RS stability in the present quantum FISG model, especially near the quantum critical point. In particular, the FISG model allows changing the occupation number of sites, so one can get a first order transition when the chemical potential exceeds a certain value. In this region, the replicon and the λ± indicate instability problems for the SG solution close to all ranges of a first order boundary.

  15. Break of universality for an Ising model with aperiodic Rudin-Shapiro interactions

    Science.gov (United States)

    Andrade, R. F. S.; Pinho, S. T. R.

    2003-08-01

    We analyze the ferromagnetic Ising model on non-Euclidean scale invariant lattices with aperiodic interactions ( J A , J B , J C , J D ) defined by Rudin-Shapiro substitution rules with Migdal-Kadanoff renormalization (MKR) and transfer matrix (TM) techniques. The analysis of the invariant sets of the zero-field MKR transformation indicates that the critical behavior, completely distinct from the one of the uniform model, is described by a new off-diagonal fixed point. This contrasts with other aperiodic models where the new critical behavior is described by a period-two cycle. With the new fixed point, values for the thermal critical exponents, α and ν, as well as the period of log-periodic oscillations, are obtained. Exact recursive maps for all thermodynamical functions are derived within the TM approach. The explicit dependence of the thermodynamical functions with respect to temperature is evaluated by the numerical iteration of the set of maps until a previously chosen convergence is achieved. They also indicate that, depending on the actual choice for the aperiodic coupling constants, the magnetic exponents (β and γ) assume different values. However the Rushbrook relation is always satisfied.

  16. Critical Finite Size Scaling Relation of the Order-Parameter Probability Distribution for the Three-Dimensional Ising Model on the Creutz Cellular Automaton

    Institute of Scientific and Technical Information of China (English)

    B. Kutlu; M. Civi

    2006-01-01

    @@ We study the order parameter probability distribution at the critical point for the three-dimensional spin-1/2 and spin-1 Ising models on the simple cubic lattice under periodic boundary conditions.

  17. Magnetic properties of doped kagomé antiferromagnet

    Science.gov (United States)

    Koretsune, Takashi; Ogata, Masao

    In order to clarify the carrier doping effect in the frustrated system, we study the t-J model on the kagomé lattice using high-temperature expansion method. As in the triangular lattice [T. Koretsune, M. Ogata, Phys. Rev. Lett. 89 (2002) 116401], the sign of hopping integral t is important in the kagomé lattice. When tOgata, J. Phys. Soc. Japan 72 (2003) 2437]. On the contrary, in the case of t>0, it is found that uniform spin susceptibility is strongly suppressed with hole doping. The peak of spin susceptibility, which is expected to be around T=J/20 in the Heisenberg model, goes to high temperature region. Furthermore, short-range magnetic correlation is enhanced with hole doping. This is interesting since nearest-neighbor spin correlation without hole doping itself is strongly enhanced by quantum fluctuation. These behavior are qualitatively similar to those of the triangular lattice. However, the difference from non-frustrated lattices as square lattice is more prominent in the kagomé lattice, which is related to the fact that frustration in the kagomé lattice is strong enough to destabilize the magnetic order in the Heisenberg model even at T=0.

  18. Radii of the E8 Gosset Circles as the Mass Excitations in the Ising Model

    CERN Document Server

    Koca, Mehmet

    2012-01-01

    The Zamolodchikov's conjecture implying the exceptional Lie group E8 seems to be validated by an experiment on the quantum phase transitions of the 1D Ising model carried out by the Coldea et. al. The E8 model which follows from the affine Toda field theory predicts 8 bound states with the mass relations in the increasing order m1, m2= tau m1, m3, m4, m5, m6=tau m3, m7= tau m4, m8= tau m5, where tau= (1+\\sqrt(5))/2 represents the golden ratio. Above relations follow from the fact that the Coxeter group W(H4) is a maximal subgroup of the Coxeter-Weyl group W(E8). These masses turn out to be proportional to the radii of the Gosset's circles on the Coxeter plane obtained by an orthogonal projection of the root system of E8 . We also note that the masses m1, m3, m4 and m5 correspond to the radii of the circles obtained by projecting the vertices of the 600-cell, a 4D polytope of the non-crystallographic Coxeter group W(H4). A special non-orthogonal projection of the simple roots on the Coxeter plane leads to exac...

  19. Coupled Ising models and interdependent discrete choices under social influence in homogeneous populations

    CERN Document Server

    del Río, Ana Fernández

    2011-01-01

    The use of statistical physics to study problems of social sciences is motivated and its current state of the art briefly reviewed, in particular for the case of discrete choice making. The coupling of two binary choices is studied in some detail, using an Ising model for each of the decision variables (the opinion or choice moments or spins, socioeconomic equivalents to the magnetic moments or spins). Toy models for two different types of coupling are studied analytically and numerically in the mean field (infinite range) approximation. This is equivalent to considering a social influence effect proportional to the fraction of adopters or average magnetisation. In the nonlocal case, the two spin variables are coupled through a Weiss mean field type term. In a socioeconomic context, this can be useful when studying individuals of two different groups, making the same decision under social influence of their own group, when their outcome is affected by the fraction of adopters of the other group. In the local ...

  20. Variational perturbation and extended Plefka approaches to dynamics on random networks: the case of the kinetic Ising model

    CERN Document Server

    Bachschmid-Romano, Ludovica; Opper, Manfred; Roudi, Yasser

    2016-01-01

    We describe and analyze some novel approaches for studying the dynamics of Ising spin glass models. We first briefly consider the variational approach based on minimizing the Kullback-Leibler divergence between independent trajectories and the real ones and note that this approach only coincides with the mean field equations from the saddle point approximation to the generating functional when the dynamics is defined through a logistic link function, which is the case for the kinetic Ising model with parallel update. We then spend the rest of the paper developing two ways of going beyond the saddle point approximation to the generating functional. In the first one, we develop a variational perturbative approximation to the generating functional by expanding the action around a quadratic function of the local fields and conjugate local fields whose parameters are optimized. We derive analytical expressions for the optimal parameters and show that when the optimization is suitably restricted, we recover the mea...

  1. Cluster Monte Carlo dynamics for the Ising model on fractal structures in dimensions between one and two

    Science.gov (United States)

    Monceau, P.; Hsiao, P.-Y.

    2003-02-01

    We study the cluster size distributions generated by the Wolff algorithm in the framework of the Ising model on Sierpinski fractals with Hausdorff dimension Df between 1 and 2. We show that these distributions exhibit a scaling property involving the magnetic exponent yh associated with one of the eigen-direction of the renormalization flows. We suggest that a single cluster tends to invade the whole lattice as Df tends towards the lower critical dimension of the Ising model, namely 1. The autocorrelation times associated with the Wolff and Swendsen-Wang algorithms enable us to calculate dynamical exponents; the cluster algorithms are shown to be more efficient in reducing the critical slowing down when Df is lowered.

  2. On an Algebraic Property of the Disordered Phase of the Ising Model with Competing Interactions on a Cayley Tree

    Science.gov (United States)

    Mukhamedov, Farrukh; Barhoumi, Abdessatar; Souissi, Abdessatar

    2016-12-01

    It is known that the disordered phase of the classical Ising model on the Caley tree is extreme in some region of the temperature. If one considers the Ising model with competing interactions on the same tree, then about the extremity of the disordered phase there is no any information. In the present paper, we first aiming to analyze the correspondence between Gibbs measures and QMC's on trees. Namely, we establish that states associated with translation invariant Gibbs measures of the model can be seen as diagonal quantum Markov chains on some quasi local algebra. Then as an application of the established correspondence, we study some algebraic property of the disordered phase of the Ising model with competing interactions on the Cayley tree of order two. More exactly, we prove that a state corresponding to the disordered phase is not quasi-equivalent to other states associated with translation invariant Gibbs measures. This result shows how the translation invariant states relate to each other, which is even a new phenomena in the classical setting. To establish the main result we basically employ methods of quantum Markov chains.

  3. Corner wetting in the two-dimensional Ising model: Monte Carlo results

    Energy Technology Data Exchange (ETDEWEB)

    Albano, E V [INIFTA, Universidad Nacional de La Plata, CC 16 Suc. 4, 1900 La Plata (Argentina); Virgiliis, A De [INIFTA, Universidad Nacional de La Plata, CC 16 Suc. 4, 1900 La Plata (Argentina); Mueller, M [Institut fuer Physik, Johannes Gutenberg Universitaet, Staudinger Weg 7, D-55099 Mainz (Germany); Binder, K [Institut fuer Physik, Johannes Gutenberg Universitaet, Staudinger Weg 7, D-55099 Mainz (Germany)

    2003-01-29

    Square LxL (L=24-128) Ising lattices with nearest neighbour ferromagnetic exchange are considered using free boundary conditions at which boundary magnetic fields are applied, i.e., at the two boundary rows ending at the lower left corner a field +h acts, while at the two boundary rows ending at the upper right corner a field -h acts. For temperatures T less than the critical temperature T{sub c} of the bulk, this boundary condition leads to the formation of two domains with opposite orientations of the magnetization direction, separated by an interface which for T larger than the filling transition temperature T{sub f} (h) runs from the upper left corner to the lower right corner, while for TT{sub f} (h) it scales as w {proportional_to}{radical} L. The distribution P (l) of the interface position l (measured along the z-direction from the corners) decays exponentially for TT{sub f} (h). Furthermore, the Monte Carlo data are compatible with (l) {proportional_to} (T{sub f} (h) - T){sup -1} and a finite size scaling of the total magnetization according to M(L, T) M-tilde ((1 - T/T{sub f} (h)){sup {nu}}{sub perp} L) with {nu}{sub perp} = 1. Unlike the findings for critical wetting in the thin film geometry of the Ising model, the Monte Carlo results for corner wetting are in very good agreement with the theoretical predictions.

  4. Surface Tension, Surface Stiffness, and Surface Width of the 3-dimensional Ising Model on a Cubic Lattice

    CERN Document Server

    Hasenbusch, M.; Hasenbusch, Martin; Pinn, Klaus

    1992-01-01

    We compute properties of the interface of the 3-dimensional Ising model for a wide range of temperatures and for interface extensions up to 64 by 64. The interface tension sigma is obtained by integrating the surface energy density over the inverse temperature beta. The surface stiffness coefficient kappa is determined. We also study universal quantities like xi^2 sigma and xi^2 kappa. The behavior of the interfacial width on lattices up to 512 times 512 times 27 is also investigated.

  5. Exact field-driven interface dynamics in the two-dimensional stochastic Ising model with helicoidal boundary conditions

    OpenAIRE

    de Mendonça, J. Ricardo G.

    2012-01-01

    We investigate the interface dynamics of the two-dimensional stochastic Ising model in an external field under helicoidal boundary conditions. At sufficiently low temperatures and fields, the dynamics of the interface is described by an exactly solvable high-spin asymmetric quantum Hamiltonian that is the infinitesimal generator of the zero range process. Generally, the critical dynamics of the interface fluctuations is in the Kardar-Parisi-Zhang universality class of critical behavior. We re...

  6. Properties of Three Pseudo-Spins in Ferroelectric or Ferro-Antiferroelectric Materials Described by a Transverse Ising Model

    Institute of Scientific and Technical Information of China (English)

    JIANG Wei; Veng-Cheong Lo

    2005-01-01

    Ferroelectric phase diagrams and the temperature dependence of polarization, dielectric properties of the three pseudo-spin in ferroelectric or ferro-antiferroelectric system described by a transverse Ising models are investigated on the basis of the effective-field theory with the differential operator technique. The effects of the transverse field and the coupling strength between the nearest-neighboring pseudo-spin on the physical properties are discussed in detail.

  7. Constructing and proving the ground state of a generalized Ising model by the cluster tree optimization algorithm

    CERN Document Server

    Huang, Wenxuan; Dacek, Stephen; Rong, Ziqin; Ding, Zhiwei; Ceder, Gerbrand

    2016-01-01

    Generalized Ising models, also known as cluster expansions, are an important tool in many areas of condensed-matter physics and materials science, as they are often used in the study of lattice thermodynamics, solid-solid phase transitions, magnetic and thermal properties of solids, and fluid mechanics. However, the problem of finding the global ground state of generalized Ising model has remained unresolved, with only a limited number of results for simple systems known. We propose a method to efficiently find the periodic ground state of a generalized Ising model of arbitrary complexity by a new algorithm which we term cluster tree optimization. Importantly, we are able to show that even in the case of an aperiodic ground state, our algorithm produces a sequence of states with energy converging to the true ground state energy, with a provable bound on error. Compared to the current state-of-the-art polytope method, this algorithm eliminates the necessity of introducing an exponential number of variables to ...

  8. Quantum correlated cluster mean-field theory applied to the transverse Ising model.

    Science.gov (United States)

    Zimmer, F M; Schmidt, M; Maziero, Jonas

    2016-06-01

    Mean-field theory (MFT) is one of the main available tools for analytical calculations entailed in investigations regarding many-body systems. Recently, there has been a surge of interest in ameliorating this kind of method, mainly with the aim of incorporating geometric and correlation properties of these systems. The correlated cluster MFT (CCMFT) is an improvement that succeeded quite well in doing that for classical spin systems. Nevertheless, even the CCMFT presents some deficiencies when applied to quantum systems. In this article, we address this issue by proposing the quantum CCMFT (QCCMFT), which, in contrast to its former approach, uses general quantum states in its self-consistent mean-field equations. We apply the introduced QCCMFT to the transverse Ising model in honeycomb, square, and simple cubic lattices and obtain fairly good results both for the Curie temperature of thermal phase transition and for the critical field of quantum phase transition. Actually, our results match those obtained via exact solutions, series expansions or Monte Carlo simulations.

  9. Effect of Electron Itineracy on Magnetism of S = 1/2 Ferromagnetic Ising Model

    Institute of Scientific and Technical Information of China (English)

    WANG Huai-Yu; WU Jian-Hua; XUN Kun

    2003-01-01

    The effect of electron itineracy on the magnetism of S=1/2 ferromagnetic Ising model is investigated by introducing a hopping term. The electron Green's function method is used to deal with this Hamiltonian. Here emphasis is made on that the magnetization is caused by the difference between the filling of spin-up and spin-down electrons.This concept is in accordance with that of band structure theory. In the zero band width limit, our results are the same as obtained by spin Green's function method. However, our method achieves more detailed physical information. The spontaneous magnetization, Curie temperature, total energy, and specific heat are calculated and investigated in detail by the densities of states. Hopping term depresses the Curie temperature but remains the order-disorder transformation still to be second order transition. Above the transition point, the energy band is the same as that of tight binding system because exchange interaction has no effect anymore. While under the transition point, the energy band splits into two subbands due to exchange interaction.

  10. Microscopic approach to critical phenomena at interfaces: An application to complete wetting in the Ising model

    Science.gov (United States)

    Orlandi, A.; Parola, A.; Reatto, L.

    2004-11-01

    We study how the formalism of the hierarchical reference theory (HRT) can be extended to inhomogeneous systems. HRT is a liquid-state theory which implements the basic ideas of the Wilson momentum-shell renormalization group (RG) to microscopic Hamiltonians. In the case of homogeneous systems, HRT provides accurate results even in the critical region, where it reproduces scaling and nonclassical critical exponents. We applied the HRT to study wetting critical phenomena in a planar geometry. Our formalism avoids the explicit definition of effective surface Hamiltonians but leads, close to the wetting transition, to the same renormalization group equation already studied by RG techiques. However, HRT also provides information on the nonuniversal quantities because it does not require any preliminary coarse graining procedure. A simple approximation to the infinite HRT set of equations is discussed. The HRT evolution equation for the surface free energy is numerically integrated in a semi-infinite three-dimensional Ising model and the complete wetting phase transition is analyzed. A renormalization of the adsorption critical amplitude and of the wetting parameter is observed. Our results are compared to available Monte Carlo simulations.

  11. Hysteresis in DNA compaction by Dps is described by an Ising model.

    Science.gov (United States)

    Vtyurina, Natalia N; Dulin, David; Docter, Margreet W; Meyer, Anne S; Dekker, Nynke H; Abbondanzieri, Elio A

    2016-05-03

    In all organisms, DNA molecules are tightly compacted into a dynamic 3D nucleoprotein complex. In bacteria, this compaction is governed by the family of nucleoid-associated proteins (NAPs). Under conditions of stress and starvation, an NAP called Dps (DNA-binding protein from starved cells) becomes highly up-regulated and can massively reorganize the bacterial chromosome. Although static structures of Dps-DNA complexes have been documented, little is known about the dynamics of their assembly. Here, we use fluorescence microscopy and magnetic-tweezers measurements to resolve the process of DNA compaction by Dps. Real-time in vitro studies demonstrated a highly cooperative process of Dps binding characterized by an abrupt collapse of the DNA extension, even under applied tension. Surprisingly, we also discovered a reproducible hysteresis in the process of compaction and decompaction of the Dps-DNA complex. This hysteresis is extremely stable over hour-long timescales despite the rapid binding and dissociation rates of Dps. A modified Ising model is successfully applied to fit these kinetic features. We find that long-lived hysteresis arises naturally as a consequence of protein cooperativity in large complexes and provides a useful mechanism for cells to adopt unique epigenetic states.

  12. High-order Fuchsian equations for the square lattice Ising model: {chi}{sup (6)}

    Energy Technology Data Exchange (ETDEWEB)

    Boukraa, S [LPTHIRM and Departement d' Aeronautique, Universite de Blida (Algeria); Hassani, S; Zenine, N [Centre de Recherche Nucleaire d' Alger, 2 Bd. Frantz Fanon, BP 399, 16000 Alger (Algeria); Jensen, I [ARC Centre of Excellence for Mathematics and Statistics of Complex Systems, Department of Mathematics and Statistics, University of Melbourne, Victoria 3010 (Australia); Maillard, J-M [LPTMC, Universite de Paris 6, Tour 24, 4eme etage, case 121, 4 Place Jussieu, 75252 Paris Cedex 05 (France)], E-mail: boukraa@mail.univ-blida.dz, E-mail: I.Jensen@ms.unimelb.edu.au, E-mail: maillard@lptmc.jussieu.fr, E-mail: njzenine@yahoo.com

    2010-03-19

    This paper deals with {chi}-tilde{sup (6)}, the six-particle contribution to the magnetic susceptibility of the square lattice Ising model. We have generated, modulo a prime, series coefficients for {chi}-tilde{sup (6)}. The length of the series is sufficient to produce the corresponding Fuchsian linear differential equation (modulo a prime). We obtain the Fuchsian linear differential equation that annihilates the 'depleted' series {phi}{sup (6)}={chi}-tilde{sup (6)} - 2/3 {chi}-tilde{sup (4)} + 2/45 {chi}-tilde{sup (2)}. The factorization of the corresponding differential operator is performed using a method of factorization modulo a prime, introduced in a previous paper. The 'depleted' differential operator is shown to have a structure similar to the corresponding operator for {chi}-tilde{sup (5)}. It splits into factors of smaller orders, with the left-most factor of order 6 being equivalent to the symmetric fifth power of the linear differential operator corresponding to the elliptic integral E. The right-most factor has a direct sum structure, and using series calculated modulo several primes, all the factors in the direct sum have been reconstructed in exact arithmetics.

  13. High order Fuchsian equations for the square lattice Ising model: {chi}-tilde{sup (5)}

    Energy Technology Data Exchange (ETDEWEB)

    Bostan, A [INRIA Paris-Rocquencourt, Domaine de Voluceau, B.P. 105 78153 Le Chesnay, Cedex (France); Boukraa, S [LPTHIRM and Departement d' Aeronautique, Universite de Blida (Algeria); Guttmann, A J; Jensen, I [ARC Centre of Excellence for Mathematics and Statistics of Complex Systems, Department of Mathematics and Statistics, University of Melbourne, Victoria 3010 (Australia); Hassani, S; Zenine, N [Centre de Recherche Nucleaire d' Alger, 2 Bd. Frantz Fanon, BP 399, 16000 Alger (Algeria); Maillard, J-M [LPTMC, UMR 7600 CNRS, Universite de Paris, Tour 24, 4eme etage, case 121, 4 Place Jussieu, 75252 Paris Cedex 05 (France)], E-mail: alin.bostan@inria.fr, E-mail: boukraa@mail.univ-blida.dz, E-mail: tonyg@ms.unimelb.edu.au, E-mail: I.Jensen@ms.unimelb.edu.au, E-mail: maillard@lptmc.jussieu.fr, E-mail: maillard@lptl.jussieu.fr, E-mail: njzenine@yahoo.com

    2009-07-10

    We consider the Fuchsian linear differential equation obtained (modulo a prime) for {chi}-tilde{sup (5)}, the five-particle contribution to the susceptibility of the square lattice Ising model. We show that one can understand the factorization of the corresponding linear differential operator from calculations using just a single prime. A particular linear combination of {chi}-tilde{sup (1)} and {chi}-tilde{sup (3)} can be removed from {chi}-tilde{sup (5)} and the resulting series is annihilated by a high order globally nilpotent linear ODE. The corresponding (minimal order) linear differential operator, of order 29, splits into factors of small orders. A fifth-order linear differential operator occurs as the left-most factor of the 'depleted' differential operator and it is shown to be equivalent to the symmetric fourth power of L{sub E}, the linear differential operator corresponding to the elliptic integral E. This result generalizes what we have found for the lower order terms {chi}-tilde{sup (3)} and {chi}-tilde{sup (4)}. We conjecture that a linear differential operator equivalent to a symmetric (n - 1) th power of L{sub E} occurs as a left-most factor in the minimal order linear differential operators for all {chi}-tilde{sup (n)}'s.

  14. Square lattice Ising model {chi}-tilde{sup (5)} ODE in exact arithmetic

    Energy Technology Data Exchange (ETDEWEB)

    Nickel, B [Department of Physics, University of Guelph, Guelph, Ontario N1G 2W1 (Canada); Jensen, I; Guttmann, A J [ARC Centre of Excellence for Mathematics and Statistics of Complex Systems, Department of Mathematics and Statistics, The University of Melbourne, Victoria 3010 (Australia); Boukraa, S [LPTHIRM and Departement d' Aeronautique, Universite de Blida, Blida (Algeria); Hassani, S; Zenine, N [Centre de Recherche Nucleaire d' Alger, 2 Bd. Frantz Fanon, BP 399, 16000 Alger (Algeria); Maillard, J-M, E-mail: bgn@physics.uoguelph.c, E-mail: I.Jensen@ms.unimelb.edu.a, E-mail: boukraa@mail.univ-blida.d, E-mail: tonyg@ms.unimelb.edu.a, E-mail: maillard@lptmc.jussieu.f, E-mail: njzenine@yahoo.co [LPTMC, UMR 7600 CNRS, Universite de Paris, Tour 24, 4eme etage, case 121, 4 Place Jussieu, 75252 Paris Cedex 05 (France)

    2010-05-14

    We obtain in exact arithmetic the order 24 linear differential operator L{sub 24} and the right-hand side E{sup (5)} of the inhomogeneous equation L{sub 24}({Phi}{sup (5)}) = E{sup (5)}, where {Phi}{sup (5)}={chi}-tilde{sup (5)}-{chi}-tilde{sup (3)}/2+{chi}-tilde{sup (1)}/120 is a linear combination of n-particle contributions to the susceptibility of the square lattice Ising model. In Bostan et al (2009 J. Phys. A: Math. Theor. 42 275209), the operator L{sub 24} (modulo a prime) was shown to factorize into L{sub 12}{sup (left){center_dot}}L{sub 12}{sup (right)}; here we prove that no further factorization of the order 12 operator L{sub 12}{sup (left)} is possible. We use the exact ODE to obtain the behaviour of {chi}-tilde{sup (5)} at the ferromagnetic critical point and to obtain a limited number of analytic continuations of {chi}-tilde{sup (5)} beyond the principal disc defined by its high temperature series. Contrary to a speculation in Boukraa et al (2008 J. Phys. A: Math. Theor. 41 455202), we find that {chi}-tilde{sup (5)} is singular at w = 1/2 on an infinite number of branches.

  15. Local and cluster critical dynamics of the 3d random-site Ising model

    Science.gov (United States)

    Ivaneyko, D.; Ilnytskyi, J.; Berche, B.; Holovatch, Yu.

    2006-10-01

    We present the results of Monte Carlo simulations for the critical dynamics of the three-dimensional site-diluted quenched Ising model. Three different dynamics are considered, these correspond to the local update Metropolis scheme as well as to the Swendsen-Wang and Wolff cluster algorithms. The lattice sizes of L=10-96 are analysed by a finite-size-scaling technique. The site dilution concentration p=0.85 was chosen to minimize the correction-to-scaling effects. We calculate numerical values of the dynamical critical exponents for the integrated and exponential autocorrelation times for energy and magnetization. As expected, cluster algorithms are characterized by lower values of dynamical critical exponent than the local one: also in the case of dilution critical slowing down is more pronounced for the Metropolis algorithm. However, the striking feature of our estimates is that they suggest that dilution leads to decrease of the dynamical critical exponent for the cluster algorithms. This phenomenon is quite opposite to the local dynamics, where dilution enhances critical slowing down.

  16. Random-field Ising model on isometric lattices: Ground states and non-Porod scattering

    Science.gov (United States)

    Bupathy, Arunkumar; Banerjee, Varsha; Puri, Sanjay

    2016-01-01

    We use a computationally efficient graph cut method to obtain ground state morphologies of the random-field Ising model (RFIM) on (i) simple cubic (SC), (ii) body-centered cubic (BCC), and (iii) face-centered cubic (FCC) lattices. We determine the critical disorder strength Δc at zero temperature with high accuracy. For the SC lattice, our estimate (Δc=2.278 ±0.002 ) is consistent with earlier reports. For the BCC and FCC lattices, Δc=3.316 ±0.002 and 5.160 ±0.002 , respectively, which are the most accurate estimates in the literature to date. The small-r behavior of the correlation function exhibits a cusp regime characterized by a cusp exponent α signifying fractal interfaces. In the paramagnetic phase, α =0.5 ±0.01 for all three lattices. In the ferromagnetic phase, the cusp exponent shows small variations due to the lattice structure. Consequently, the interfacial energy Ei(L ) for an interface of size L is significantly different for the three lattices. This has important implications for nonequilibrium properties.

  17. Influence of thermal fluctuations on the geometry of interfaces of the quenched Ising model.

    Science.gov (United States)

    Corberi, Federico; Lippiello, Eugenio; Zannetti, Marco

    2008-07-01

    We study the role of the quench temperature Tf in the phase-ordering kinetics of the Ising model with single spin flip in d=2,3 . Equilibrium interfaces are flat at Tf=0 , whereas at Tf>0 they are curved and rough (above the roughening temperature in d=3 ). We show, by means of scaling arguments and numerical simulations, that this geometrical difference is important for the phase-ordering kinetics as well. In particular, while the growth exponent z=2 of the size of domains L(t) approximately t 1/z is unaffected by Tf, other exponents related to the interface geometry take different values at Tf=0 or Tf>0 . For Tf>0 a crossover phenomenon is observed from an early stage where interfaces are still flat and the system behaves as at Tf=0 , to the asymptotic regime with curved interfaces characteristic of Tf>0 . Furthermore, it is shown that the roughening length, although subdominant with respect to L(t) , produces appreciable correction to scaling up to very long times in d=2 .

  18. Test of quantum thermalization in the two-dimensional transverse-field Ising model

    Science.gov (United States)

    Blaß, Benjamin; Rieger, Heiko

    2016-12-01

    We study the quantum relaxation of the two-dimensional transverse-field Ising model after global quenches with a real-time variational Monte Carlo method and address the question whether this non-integrable, two-dimensional system thermalizes or not. We consider both interaction quenches in the paramagnetic phase and field quenches in the ferromagnetic phase and compare the time-averaged probability distributions of non-conserved quantities like magnetization and correlation functions to the thermal distributions according to the canonical Gibbs ensemble obtained with quantum Monte Carlo simulations at temperatures defined by the excess energy in the system. We find that the occurrence of thermalization crucially depends on the quench parameters: While after the interaction quenches in the paramagnetic phase thermalization can be observed, our results for the field quenches in the ferromagnetic phase show clear deviations from the thermal system. These deviations increase with the quench strength and become especially clear comparing the shape of the thermal and the time-averaged distributions, the latter ones indicating that the system does not completely lose the memory of its initial state even for strong quenches. We discuss our results with respect to a recently formulated theorem on generalized thermalization in quantum systems.

  19. Critical Casimir force scaling functions of the two-dimensional Ising model at finite aspect ratios

    Science.gov (United States)

    Hobrecht, Hendrik; Hucht, Alfred

    2017-02-01

    We present a systematic method to calculate the universal scaling functions for the critical Casimir force and the according potential of the two-dimensional Ising model with various boundary conditions. Therefore we start with the dimer representation of the corresponding partition function Z on an L× M square lattice, wrapped around a torus with aspect ratio ρ =L/M . By assuming periodic boundary conditions and translational invariance in at least one direction, we systematically reduce the problem to a 2× 2 transfer matrix representation. For the torus we first reproduce the results by Kaufman and then give a detailed calculation of the scaling functions. Afterwards we present the calculation for the cylinder with open boundary conditions. All scaling functions are given in form of combinations of infinite products and integrals. Our results reproduce the known scaling functions in the limit of thin films ρ \\to 0 . Additionally, for the cylinder at criticality our results confirm the predictions from conformal field theory.

  20. Study of spin crossover nanoparticles thermal hysteresis using FORC diagrams on an Ising-like model

    Energy Technology Data Exchange (ETDEWEB)

    Atitoaie, Alexandru; Tanasa, Radu, E-mail: radu.tanasa@uaic.ro; Stancu, Alexandru; Enachescu, Cristian, E-mail: cristian.enachescu@uaic.ro

    2014-11-15

    Recent developments in the synthesis and characterization of spin crossover (SCO) nanoparticles and their prospects of switching at molecular level turned these bistable compounds into possible candidates for replacing the materials used in recording media industry for development of solid state pressure and temperature sensors or for bringing contributions in engineering. Compared to bulk samples with the same chemical structure, SCO nanoparticles display different characteristics of the hysteretic and relaxation properties like the shift of the transition temperature towards lower values along with decrease of the hysteresis width with nanoparticles size. Using an Ising-like model with specific boundary conditions within a Monte Carlo procedure, we here reproduce most of the hysteretic properties of SCO nanoparticles by considering the interaction between spin crossover edge molecules and embedding surfactant molecules and we propose a complex analysis concerning the effect of the interactions and sizes during the thermal transition in systems of SCO nanoparticles by using the First Order Reversal Curves diagram method and by comparison with similar effects in mixed crystal systems. - Highlights: • The influence of size effects in spin crossover nanoparticles is analyzed. • The environment shifts the hysteresis loop towards lower temperatures. • First Order Reversal Curves technique is employed. • One determines the distributions of switching temperatures. • One disentangles between kinetics and non-kinetic parts of the hysteresis.

  1. Minority-spin dynamics in the nonhomogeneous Ising model: Diverging time scales and exponents

    Science.gov (United States)

    Mullick, Pratik; Sen, Parongama

    2016-05-01

    We investigate the dynamical behavior of the Ising model under a zero-temperature quench with the initial fraction of up spins 0 ≤x ≤1 . In one dimension, the known results for persistence probability are verified; it shows algebraic decay for both up and down spins asymptotically with different exponents. It is found that the conventional finite-size scaling is valid here. In two dimensions, however, the persistence probabilities are no longer algebraic; in particular for x ≤0.5 , persistence for the up (minority) spins shows the behavior Pmin(t ) ˜t-γexp[-(t/τ ) δ] with time t , while for the down (majority) spins, Pmaj(t ) approaches a finite value. We find that the timescale τ diverges as (xc-x ) -λ, where xc=0.5 and λ ≃2.31 . The exponent γ varies as θ2 d+c0(xc-x ) β where θ2 d≃0.215 is very close to the persistence exponent in two dimensions; β ≃1 . The results in two dimensions can be understood qualitatively by studying the exit probability, which for different system size is found to have the form E (x ) =f [(x/-xc xc) L1 /ν] , with ν ≈1.47 . This result suggests that τ ˜Lz ˜ , where z ˜=λ/ν =1.57 ±0.11 is an exponent not explored earlier.

  2. Exploring the renormalization of quantum discord and Bell non-locality in the one-dimensional transverse Ising model

    Science.gov (United States)

    Liu, Cheng-cheng; Shi, Jia-dong; Ding, Zhi-yong; Ye, Liu

    2016-08-01

    In this paper, the effect of external magnet field g on the relationship among the quantum discord, Bell non-locality and quantum phase transition by employing quantum renormalization-group (QRG) method in the one-dimensional transverse Ising model is investigated. In our model, external magnet field g can influence the phase diagrams. The results have shown that both the two quantum correlation measures can develop two saturated values, which are associated with two distinct phases: long-ranged ordered Ising phase and the paramagnetic phase with the number of QRG iterations increasing. Additionally, quantum non-locality always existent in the long-ranged ordered Ising phase no matter whatever the value of g is and what times QRG steps are carried out and we conclude that the quantum non-locality always exists not only suitable for the two sites of block, but for nearest-neighbor blocks in the long-ranged ordered Ising phase. However, the block-block correlation in the paramagnetic phase is not strong enough to violate the Bell-CHSH inequality as the size of system becomes large. Furthermore, when the system violates the CHSH inequality, i.e., satisfies quantum non-locality, it needs to be entangled. On the other way, if the system obeys the CHSH inequality, it may be entangled or not. To gain further insight, the non-analytic and scaling behavior of QD and Bell non-locality have also been analyzed in detail and this phenomenon indicates that the behavior of the correlation can perfectly help one to observe the quantum critical properties of the model.

  3. Random-field Ising model: Insight from zero-temperature simulations

    Directory of Open Access Journals (Sweden)

    P.E. Theodorakis

    2014-12-01

    Full Text Available We enlighten some critical aspects of the three-dimensional (d=3 random-field Ising model (RFIM from simulations performed at zero temperature. We consider two different, in terms of the field distribution, versions of model, namely a Gaussian RFIM and an equal-weight trimodal RFIM. By implementing a computational approach that maps the ground-state of the system to the maximum-flow optimization problem of a network, we employ the most up-to-date version of the push-relabel algorithm and simulate large ensembles of disorder realizations of both models for a broad range of random-field values and systems sizes V=LxLxL, where L denotes linear lattice size and Lmax=156. Using as finite-size measures the sample-to-sample fluctuations of various quantities of physical and technical origin, and the primitive operations of the push-relabel algorithm, we propose, for both types of distributions, estimates of the critical field hmax and the critical exponent ν of the correlation length, the latter clearly suggesting that both models share the same universality class. Additional simulations of the Gaussian RFIM at the best-known value of the critical field provide the magnetic exponent ratio β/ν with high accuracy and clear out the controversial issue of the critical exponent α of the specific heat. Finally, we discuss the infinite-limit size extrapolation of energy- and order-parameter-based noise to signal ratios related to the self-averaging properties of the model, as well as the critical slowing down aspects of the algorithm.

  4. From network reliability to the Ising model: A parallel scheme for estimating the joint density of states

    Science.gov (United States)

    Ren, Yihui; Eubank, Stephen; Nath, Madhurima

    2016-10-01

    Network reliability is the probability that a dynamical system composed of discrete elements interacting on a network will be found in a configuration that satisfies a particular property. We introduce a reliability property, Ising feasibility, for which the network reliability is the Ising model's partition function. As shown by Moore and Shannon, the network reliability can be separated into two factors: structural, solely determined by the network topology, and dynamical, determined by the underlying dynamics. In this case, the structural factor is known as the joint density of states. Using methods developed to approximate the structural factor for other reliability properties, we simulate the joint density of states, yielding an approximation for the partition function. Based on a detailed examination of why naïve Monte Carlo sampling gives a poor approximation, we introduce a parallel scheme for estimating the joint density of states using a Markov-chain Monte Carlo method with a spin-exchange random walk. This parallel scheme makes simulating the Ising model in the presence of an external field practical on small computer clusters for networks with arbitrary topology with ˜106 energy levels and more than 10308 microstates.

  5. Degenerate Ising model for atomistic simulation of crystal-melt interfaces

    Energy Technology Data Exchange (ETDEWEB)

    Schebarchov, D., E-mail: Dmitri.Schebarchov@gmail.com [University Chemical Laboratories, Lensfield Road, Cambridge CB2 1EW (United Kingdom); Schulze, T. P., E-mail: schulze@math.utk.edu [Department of Mathematics, University of Tennessee, Knoxville, Tennessee 37996-1300 (United States); Hendy, S. C. [The MacDiarmid Institute for Advanced Materials and Nanotechnology, School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington 6140 (New Zealand); Department of Physics, University of Auckland, Auckland 1010 (New Zealand)

    2014-02-21

    One of the simplest microscopic models for a thermally driven first-order phase transition is an Ising-type lattice system with nearest-neighbour interactions, an external field, and a degeneracy parameter. The underlying lattice and the interaction coupling constant control the anisotropic energy of the phase boundary, the field strength represents the bulk latent heat, and the degeneracy quantifies the difference in communal entropy between the two phases. We simulate the (stochastic) evolution of this minimal model by applying rejection-free canonical and microcanonical Monte Carlo algorithms, and we obtain caloric curves and heat capacity plots for square (2D) and face-centred cubic (3D) lattices with periodic boundary conditions. Since the model admits precise adjustment of bulk latent heat and communal entropy, neither of which affect the interface properties, we are able to tune the crystal nucleation barriers at a fixed degree of undercooling and verify a dimension-dependent scaling expected from classical nucleation theory. We also analyse the equilibrium crystal-melt coexistence in the microcanonical ensemble, where we detect negative heat capacities and find that this phenomenon is more pronounced when the interface is the dominant contributor to the total entropy. The negative branch of the heat capacity appears smooth only when the equilibrium interface-area-to-volume ratio is not constant but varies smoothly with the excitation energy. Finally, we simulate microcanonical crystal nucleation and subsequent relaxation to an equilibrium Wulff shape, demonstrating the model's utility in tracking crystal-melt interfaces at the atomistic level.

  6. Degenerate Ising model for atomistic simulation of crystal-melt interfaces

    Science.gov (United States)

    Schebarchov, D.; Schulze, T. P.; Hendy, S. C.

    2014-02-01

    One of the simplest microscopic models for a thermally driven first-order phase transition is an Ising-type lattice system with nearest-neighbour interactions, an external field, and a degeneracy parameter. The underlying lattice and the interaction coupling constant control the anisotropic energy of the phase boundary, the field strength represents the bulk latent heat, and the degeneracy quantifies the difference in communal entropy between the two phases. We simulate the (stochastic) evolution of this minimal model by applying rejection-free canonical and microcanonical Monte Carlo algorithms, and we obtain caloric curves and heat capacity plots for square (2D) and face-centred cubic (3D) lattices with periodic boundary conditions. Since the model admits precise adjustment of bulk latent heat and communal entropy, neither of which affect the interface properties, we are able to tune the crystal nucleation barriers at a fixed degree of undercooling and verify a dimension-dependent scaling expected from classical nucleation theory. We also analyse the equilibrium crystal-melt coexistence in the microcanonical ensemble, where we detect negative heat capacities and find that this phenomenon is more pronounced when the interface is the dominant contributor to the total entropy. The negative branch of the heat capacity appears smooth only when the equilibrium interface-area-to-volume ratio is not constant but varies smoothly with the excitation energy. Finally, we simulate microcanonical crystal nucleation and subsequent relaxation to an equilibrium Wulff shape, demonstrating the model's utility in tracking crystal-melt interfaces at the atomistic level.

  7. The interface free energy: Comparison of accurate Monte Carlo results for the 3D Ising model with effective interface models

    CERN Document Server

    Caselle, Michele; Panero, Marco

    2007-01-01

    We provide accurate Monte Carlo results for the free energy of interfaces with periodic boundary conditions in the 3D Ising model. We study a large range of inverse temperatures, allowing to control corrections to scaling. In addition to square interfaces, we study rectangular interfaces for a large range of aspect ratios u=L_1/L_2. Our numerical results are compared with predictions of effective interface models. This comparison verifies clearly the effective Nambu-Goto model up to two-loop order. Our data also allow us to obtain the estimates T_c sigma^-1/2=1.235(2), m_0++ sigma^-1/2=3.037(16) and R_+=f_+ sigma_0^2 =0.387(2), which are more precise than previous ones.

  8. Tunable two-dimensional arrays of single Rydberg atoms for realizing quantum Ising models.

    Science.gov (United States)

    Labuhn, Henning; Barredo, Daniel; Ravets, Sylvain; de Léséleuc, Sylvain; Macrì, Tommaso; Lahaye, Thierry; Browaeys, Antoine

    2016-06-30

    Spin models are the prime example of simplified many-body Hamiltonians used to model complex, strongly correlated real-world materials. However, despite the simplified character of such models, their dynamics often cannot be simulated exactly on classical computers when the number of particles exceeds a few tens. For this reason, quantum simulation of spin Hamiltonians using the tools of atomic and molecular physics has become a very active field over the past years, using ultracold atoms or molecules in optical lattices, or trapped ions. All of these approaches have their own strengths and limitations. Here we report an alternative platform for the study of spin systems, using individual atoms trapped in tunable two-dimensional arrays of optical microtraps with arbitrary geometries, where filling fractions range from 60 to 100 per cent. When excited to high-energy Rydberg D states, the atoms undergo strong interactions whose anisotropic character opens the way to simulating exotic matter. We illustrate the versatility of our system by studying the dynamics of a quantum Ising-like spin-1/2 system in a transverse field with up to 30 spins, for a variety of geometries in one and two dimensions, and for a wide range of interaction strengths. For geometries where the anisotropy is expected to have small effects on the dynamics, we find excellent agreement with ab initio simulations of the spin-1/2 system, while for strongly anisotropic situations the multilevel structure of the D states has a measurable influence. Our findings establish arrays of single Rydberg atoms as a versatile platform for the study of quantum magnetism.

  9. CRYSTAL-FIELD AND TRANSVERSE-FIELD EFFECTS OF THE SPIN-ONE ISING MODEL

    Institute of Scientific and Technical Information of China (English)

    宋为基; 杨传章

    1993-01-01

    A mean-field approximation (MFA) is used to treat the crystal-field and transverse-field effects of the spin-1 Ising modle in the presence of longitudinal field. In spite of its simplicity, this scheme still gives the satisfied results.

  10. Staircase of crystal phases of hard-core bosons on the kagome lattice

    Science.gov (United States)

    Huerga, Daniel; Capponi, Sylvain; Dukelsky, Jorge; Ortiz, Gerardo

    2016-10-01

    We study the quantum phase diagram of a system of hard-core bosons on the kagome lattice with nearest-neighbor repulsive interactions, for arbitrary densities, by means of the hierarchical mean-field theory and exact diagonalization techniques. This system is isomorphic to the spin S =1 /2 XXZ model in presence of an external magnetic field, a paradigmatic example of frustrated quantum magnetism. In the nonfrustrated regime, we find two crystal phases at densities 1/3 and 2/3 that melt into a superfluid phase when increasing the hopping amplitude, in semiquantitative agreement with quantum Monte Carlo computations. In the frustrated regime and away from half-filling, we find a series of plateaux with densities commensurate with powers of 1/3. The broader density plateaux (at densities 1/3 and 2/3) are remnants of the classical degeneracy in the Ising limit. For densities near half-filling, this staircase of crystal phases melts into a superfluid, which displays finite chiral currents when computed with clusters having an odd number of sites. Both the staircase of crystal phases and the superfluid phase prevail in the noninteracting limit, suggesting that the lowest dispersionless single-particle band may be at the root of this phenomenon.

  11. Effective potential of the three-dimensional Ising model: The pseudo-ɛ expansion study

    Science.gov (United States)

    Sokolov, A. I.; Kudlis, A.; Nikitina, M. A.

    2017-08-01

    The ratios R2k of renormalized coupling constants g2k that enter the effective potential and small-field equation of state acquire the universal values at criticality. They are calculated for the three-dimensional scalar λϕ4 field theory (3D Ising model) within the pseudo-ɛ expansion approach. Pseudo-ɛ expansions for the critical values of g6, g8, g10, R6 =g6 / g42 , R8 =g8 / g43 and R10 =g10 / g44 originating from the five-loop renormalization group (RG) series are derived. Pseudo-ɛ expansions for the sextic coupling have rapidly diminishing coefficients, so addressing Padé approximants yields proper numerical results. Use of Padé-Borel-Leroy and conformal mapping resummation techniques further improves the accuracy leading to the values R6* = 1.6488 and R6* = 1.6490 which are in a brilliant agreement with the result of advanced lattice calculations. For the octic coupling the numerical structure of the pseudo-ɛ expansions is less favorable. Nevertheless, the conform-Borel resummation gives R8* = 0.868, the number being close to the lattice estimate R8* = 0.871 and compatible with the result of 3D RG analysis R8* = 0.857. Pseudo-ɛ expansions for R10* and g10* are also found to have much smaller coefficients than those of the original RG series. They remain, however, fast growing and big enough to prevent obtaining fair numerical estimates.

  12. Adaptive multi-GPU Exchange Monte Carlo for the 3D Random Field Ising Model

    Science.gov (United States)

    Navarro, Cristóbal A.; Huang, Wei; Deng, Youjin

    2016-08-01

    This work presents an adaptive multi-GPU Exchange Monte Carlo approach for the simulation of the 3D Random Field Ising Model (RFIM). The design is based on a two-level parallelization. The first level, spin-level parallelism, maps the parallel computation as optimal 3D thread-blocks that simulate blocks of spins in shared memory with minimal halo surface, assuming a constant block volume. The second level, replica-level parallelism, uses multi-GPU computation to handle the simulation of an ensemble of replicas. CUDA's concurrent kernel execution feature is used in order to fill the occupancy of each GPU with many replicas, providing a performance boost that is more notorious at the smallest values of L. In addition to the two-level parallel design, the work proposes an adaptive multi-GPU approach that dynamically builds a proper temperature set free of exchange bottlenecks. The strategy is based on mid-point insertions at the temperature gaps where the exchange rate is most compromised. The extra work generated by the insertions is balanced across the GPUs independently of where the mid-point insertions were performed. Performance results show that spin-level performance is approximately two orders of magnitude faster than a single-core CPU version and one order of magnitude faster than a parallel multi-core CPU version running on 16-cores. Multi-GPU performance is highly convenient under a weak scaling setting, reaching up to 99 % efficiency as long as the number of GPUs and L increase together. The combination of the adaptive approach with the parallel multi-GPU design has extended our possibilities of simulation to sizes of L = 32 , 64 for a workstation with two GPUs. Sizes beyond L = 64 can eventually be studied using larger multi-GPU systems.

  13. Magnetization process in the exactly solved spin-1/2 Ising-Heisenberg model on decorated Bethe lattices

    Directory of Open Access Journals (Sweden)

    J. Strečka

    2012-12-01

    Full Text Available The spin-1/2 Ising-Heisenberg model on diamond-like decorated Bethe lattices is exactly solved in the presence of the longitudinal magnetic field by combining the decoration-iteration mapping transformation with the method of exact recursion relations. In particular, the ground state and low-temperature magnetization process of the ferrimagnetic version of the considered model is investigated in detail. Three different magnetization scenarios with up to two consecutive fractional magnetization plateaus were found, whereas the intermediate magnetization plateau may either correspond to the classical ferrimagnetic spin arrangement and/or the field-induced quantum ferrimagnetic spin ordering without any classical counterpart.

  14. Generic Ising trees

    DEFF Research Database (Denmark)

    Durhuus, Bergfinnur Jøgvan; Napolitano, George Maria

    2012-01-01

    The Ising model on a class of infinite random trees is defined as a thermodynamiclimit of finite systems. A detailed description of the corresponding distribution of infinite spin configurations is given. As an application, we study the magnetization properties of such systems and prove that they......The Ising model on a class of infinite random trees is defined as a thermodynamiclimit of finite systems. A detailed description of the corresponding distribution of infinite spin configurations is given. As an application, we study the magnetization properties of such systems and prove...... that they exhibit no spontaneous magnetization. Furthermore, the values of the Hausdorff and spectral dimensions of the underlying trees are calculated and found to be, respectively,¯dh =2 and¯ds = 4/3....

  15. Study of Damage Propagation at the Interface Localization-Delocalization Transition of the Confined Ising Model

    OpenAIRE

    Puzzo, M. Leticia Rubio; Albano,Ezequiel V.

    2007-01-01

    The propagation of damage in a confined magnetic Ising film, with short range competing magnetic fields ($h$) acting at opposite walls, is studied by means of Monte Carlo simulations. Due to the presence of the fields, the film undergoes a wetting transition at a well defined critical temperature $T_w(h)$. In fact, the competing fields causes the occurrence of an interface between magnetic domains of different orientation. For $T T_w(h)$) such interface is bounded (unbounded) ...

  16. Nature of chiral spin liquids on the kagome lattice

    Science.gov (United States)

    Wietek, Alexander; Sterdyniak, Antoine; Läuchli, Andreas M.

    2015-09-01

    We investigate the stability and the nature of the chiral spin liquids which were recently uncovered in extended Heisenberg models on the kagome lattice. Using a Gutzwiller projected wave function approach, i.e., a parton construction, we obtain large overlaps with ground states of these extended Heisenberg models. We further suggest that the appearance of the chiral spin liquid in the time-reversal invariant case is linked to a classical transition line between two magnetically ordered phases.

  17. Complexity of Ising Polynomials

    CERN Document Server

    Kotek, Tomer

    2011-01-01

    This paper deals with the partition function of the Ising model from statistical mechanics, which is used to study phase transitions in physical systems. A special case of interest is that of the Ising model with constant energies and external field. One may consider such an Ising system as a simple graph together with vertex and edge weight values. When these weights are considered indeterminates, the partition function for the constant case is a trivariate polynomial Z(G;x,y,z). This polynomial was studied with respect to its approximability by L. A. Goldberg, M. Jerrum and M. Patersonin 2003. Z(G;x,y,z) generalizes a bivariate polynomial Z(G;t,y), which was studied in by D. Andr\\'{e}n and K. Markstr\\"{o}m in 2009. We consider the complexity of Z(G;t,y) and Z(G;x,y,z) in comparison to that of the Tutte polynomial, which is well-known to be closely related to the Potts model in the absence of an external field. We show that Z(G;\\x,\\y,\\z) is #P-hard to evaluate at all points in $mathbb{Q}^3$, except those in ...

  18. Thermodynamical Properties of Spin-3/2 Ising Model in a Longitudinal Random Field with Crystal Field

    Institute of Scientific and Technical Information of China (English)

    LIANGYa-Qiu; WEIGuo-Zhu; ZHANGHong; SONGGuo-Li

    2004-01-01

    A theoretical study of a spin-3/2 Ising model in a longitudinal random field with crystal field is studied by using of the effective-field theory with correlations. The phase diagrams and the behavior of the tricritical point are investigated numerically for the honeycomb lattice when the random field is bimodal. In particular, the specific heat and the internal energy are examined in detail for the system with a crystal-field constant in the critical region where the ground-state configuration may change from the spin-3/2 state to the spin-1/2 state. We find many interesting phenomena in the system.

  19. Depinning transition of a driven interface in the random-field Ising model around the upper critical dimension.

    Science.gov (United States)

    Roters, L; Lübeck, S; Usadel, K D

    2002-12-01

    We investigate the depinning transition for driven interfaces in the random-field Ising model for various dimensions. We consider the order parameter as a function of the control parameter (driving field) and examine the effect of thermal fluctuations. Although thermal fluctuations drive the system away from criticality, the order parameter obeys a certain scaling law for sufficiently low temperatures and the corresponding exponents are determined. Our results suggest that the so-called upper critical dimension of the depinning transition is five and that the systems belongs to the universality class of the quenched Edward-Wilkinson equation.

  20. Phase Diagram and Tricritical Behavior of a Spin-2 Transverse Ising Model in aRandom Field

    Institute of Scientific and Technical Information of China (English)

    LIANGYa-Qiu; WEIGuo-Zhu; SONGLi-Li; SONGGuo-Li; ZANGShu-Liang

    2004-01-01

    The phase diagrams of a spin-2 transverse Ising model with a random field on honeycomb, square, and simple-cubic lattices, respectively, are investigated within the framework of an effective-field theory with correlations.We find the behavior of the tricritical point and the reentrant phenomenon for the system with any coordination number z, when the applied random field is bimodal. The behavior of the tricritical point is also examined as a function of applied transverse field. The reentrant phenomenon comes from the competition between the transverse field and the random field.

  1. On the Location of the 1-particle Branch of the Spectrum of the Disordered Stochastic Ising Model

    OpenAIRE

    2003-01-01

    We analyse the lower non trivial part of the spectrum of the generator of the Glauber dynamics, which we consider a positive operator, for a d-dimensional nearest neighbour Ising model with a bounded random potential. We prove conjecture 1 in a paper by Albeverio et al.(referred as [AMSZ]) that is, for sufficently large values of the temperature, the first band of the spectrum of the generator of the process coincides with a closed non random segment of the real line.

  2. Assisted finite-rate adiabatic passage across a quantum critical point: exact solution for the quantum Ising model.

    Science.gov (United States)

    del Campo, Adolfo; Rams, Marek M; Zurek, Wojciech H

    2012-09-14

    The dynamics of a quantum phase transition is inextricably woven with the formation of excitations, as a result of critical slowing down in the neighborhood of the critical point. We design a transitionless quantum driving through a quantum critical point, allowing one to access the ground state of the broken-symmetry phase by a finite-rate quench of the control parameter. The method is illustrated in the one-dimensional quantum Ising model in a transverse field. Driving through the critical point is assisted by an auxiliary Hamiltonian, for which the interplay between the range of the interaction and the modes where excitations are suppressed is elucidated.

  3. Finite-size scaling of the magnetization probability density for the critical Ising model in slab geometry

    Science.gov (United States)

    Lopes Cardozo, David; Holdsworth, Peter C. W.

    2016-04-01

    The magnetization probability density in d  =  2 and 3 dimensional Ising models in slab geometry of volume L\\paralleld-1× {{L}\\bot} is computed through Monte-Carlo simulation at the critical temperature and zero magnetic field. The finite-size scaling of this distribution and its dependence on the system aspect-ratio ρ =\\frac{{{L}\\bot}}{{{L}\\parallel}} and boundary conditions are discussed. In the limiting case ρ \\to 0 of a macroscopically large slab ({{L}\\parallel}\\gg {{L}\\bot} ) the distribution is found to scale as a Gaussian function for all tested system sizes and boundary conditions.

  4. Thermodynamical Properties of Spin-3/2 Ising Model in a Longitudinal Random Field with Crystal Field

    Institute of Scientific and Technical Information of China (English)

    LIANG Ya-Qiu; WEI Guo-Zhu; ZHANG Hong; SONG Guo-Li

    2004-01-01

    A theoretical study of a spin-3/2 Ising model in a longitudinal random field with crystal field is studiedby using of the effective-field theory with correlations. The phase diagrams and the behavior of the tricritical point areinvestigated numerically for the honeycomb lattice when the randorm field is bimodal. In particular, the specific heatand the internal energy are examined in detail for the system with a crystal-field constant in the critical region wherethe ground-state configuration may change from the spin-3/2 state to the spin-1/2 state. We find many interestingphenomena in the system.

  5. Critical endpoint behavior in an asymmetric Ising model: application of Wang-Landau sampling to calculate the density of states.

    Science.gov (United States)

    Tsai, Shan-Ho; Wang, Fugao; Landau, D P

    2007-06-01

    Using the Wang-Landau sampling method with a two-dimensional random walk we determine the density of states for an asymmetric Ising model with two- and three-body interactions on a triangular lattice, in the presence of an external field. With an accurate density of states we were able to map out the phase diagram accurately and perform quantitative finite-size analyses at, and away from, the critical endpoint. We observe a clear divergence of the curvature of the spectator phase boundary and of the magnetization coexistence diameter derivative at the critical endpoint, and the exponents for both divergences agree well with previous theoretical predictions.

  6. Ising and Bloch domain walls in a two-dimensional parametrically driven Ginzburg-Landau equation model with nonlinearity management

    DEFF Research Database (Denmark)

    Gaididei, Yu. B.; Christiansen, Peter Leth

    2008-01-01

    We study a parametrically driven Ginzburg-Landau equation model with nonlinear management. The system is made of laterally coupled long active waveguides placed along a circumference. Stationary solutions of three kinds are found: periodic Ising states and two types of Bloch states, staggered...... and unstaggered. The stability of these states is investigated analytically and numerically. The nonlinear dynamics of the Bloch states are described by a complex Ginzburg-Landau equation with linear and nonlinear parametric driving. The switching between the staggered and unstaggered Bloch states under...

  7. Critical endpoint behavior in an asymmetric Ising model: Application of Wang-Landau sampling to calculate the density of states

    Science.gov (United States)

    Tsai, Shan-Ho; Wang, Fugao; Landau, D. P.

    2007-06-01

    Using the Wang-Landau sampling method with a two-dimensional random walk we determine the density of states for an asymmetric Ising model with two- and three-body interactions on a triangular lattice, in the presence of an external field. With an accurate density of states we were able to map out the phase diagram accurately and perform quantitative finite-size analyses at, and away from, the critical endpoint. We observe a clear divergence of the curvature of the spectator phase boundary and of the magnetization coexistence diameter derivative at the critical endpoint, and the exponents for both divergences agree well with previous theoretical predictions.

  8. Interface-roughening phase diagram of the three-dimensional Ising model for all interaction anisotropies from hard-spin mean-field theory.

    Science.gov (United States)

    Cağlar, Tolga; Berker, A Nihat

    2011-11-01

    The roughening phase diagram of the d=3 Ising model with uniaxially anisotropic interactions is calculated for the entire range of anisotropy, from decoupled planes to the isotropic model to the solid-on-solid model, using hard-spin mean-field theory. The phase diagram contains the line of ordering phase transitions and, at lower temperatures, the line of roughening phase transitions, where the interface between ordered domains roughens. Upon increasing the anisotropy, roughening transition temperatures settle after the isotropic case, whereas the ordering transition temperature increases to infinity. The calculation is repeated for the d=2 Ising model for the full range of anisotropy, yielding no roughening transition.

  9. From Holonomy of the Ising Model Form Factors to n-Fold Integrals and the Theory of Elliptic Curves

    Directory of Open Access Journals (Sweden)

    Salah Boukraa

    2007-10-01

    Full Text Available We recall the form factors $f^(j_{N,N}$ corresponding to the $lambda$-extension $C(N,N; lambda$ of the two-point diagonal correlation function of the Ising model on the square lattice and their associated linear differential equations which exhibit both a "Russian-doll" nesting, and a decomposition of the linear differential operators as a direct sum of operators (equivalent to symmetric powers of the differential operator of the complete elliptic integral $E$. The scaling limit of these differential operators breaks the direct sum structure but not the "Russian doll" structure, the "scaled" linear differential operators being no longer Fuchsian. We then introduce some multiple integrals of the Ising class expected to have the same singularities as the singularities of the $n$-particle contributions $chi^{(n}$ to the susceptibility of the square lattice Ising model. We find the Fuchsian linear differential equations satisfied by these multiple integrals for $n = 1, 2, 3, 4$ and, only modulo a prime, for $n = 5$ and 6, thus providing a large set of (possible new singularities of the $chi^{(n}$. We get the location of these singularities by solving the Landau conditions. We discuss the mathematical, as well as physical, interpretation of these new singularities. Among the singularities found, we underline the fact that the quadratic polynomial condition $1 + 3w + 4w^2 = 0$, that occurs in the linear differential equation of $chi^{(3}$, actually corresponds to the occurrence of complex multiplication for elliptic curves. The interpretation of complex multiplication for elliptic curves as complex fixed points of generators of the exact renormalization group is sketched. The other singularities occurring in our multiple integrals are not related to complex multiplication situations, suggesting a geometric interpretation in terms of more general (motivic mathematical structures beyond the theory of elliptic curves. The scaling limit of the (lattice

  10. Large pseudocounts and L2-norm penalties are necessary for the mean-field inference of Ising and Potts models

    Science.gov (United States)

    Barton, J. P.; Cocco, S.; De Leonardis, E.; Monasson, R.

    2014-07-01

    The mean-field (MF) approximation offers a simple, fast way to infer direct interactions between elements in a network of correlated variables, a common, computationally challenging problem with practical applications in fields ranging from physics and biology to the social sciences. However, MF methods achieve their best performance with strong regularization, well beyond Bayesian expectations, an empirical fact that is poorly understood. In this work, we study the influence of pseudocount and L2-norm regularization schemes on the quality of inferred Ising or Potts interaction networks from correlation data within the MF approximation. We argue, based on the analysis of small systems, that the optimal value of the regularization strength remains finite even if the sampling noise tends to zero, in order to correct for systematic biases introduced by the MF approximation. Our claim is corroborated by extensive numerical studies of diverse model systems and by the analytical study of the m-component spin model for large but finite m. Additionally, we find that pseudocount regularization is robust against sampling noise and often outperforms L2-norm regularization, particularly when the underlying network of interactions is strongly heterogeneous. Much better performances are generally obtained for the Ising model than for the Potts model, for which only couplings incoming onto medium-frequency symbols are reliably inferred.

  11. Ising model with conserved magnetization on the human connectome: Implications on the relation structure-function in wakefulness and anesthesia

    Science.gov (United States)

    Stramaglia, S.; Pellicoro, M.; Angelini, L.; Amico, E.; Aerts, H.; Cortés, J. M.; Laureys, S.; Marinazzo, D.

    2017-04-01

    Dynamical models implemented on the large scale architecture of the human brain may shed light on how a function arises from the underlying structure. This is the case notably for simple abstract models, such as the Ising model. We compare the spin correlations of the Ising model and the empirical functional brain correlations, both at the single link level and at the modular level, and show that their match increases at the modular level in anesthesia, in line with recent results and theories. Moreover, we show that at the peak of the specific heat (the critical state), the spin correlations are minimally shaped by the underlying structural network, explaining how the best match between the structure and function is obtained at the onset of criticality, as previously observed. These findings confirm that brain dynamics under anesthesia shows a departure from criticality and could open the way to novel perspectives when the conserved magnetization is interpreted in terms of a homeostatic principle imposed to neural activity.

  12. Large pseudocounts and L2-norm penalties are necessary for the mean-field inference of Ising and Potts models.

    Science.gov (United States)

    Barton, J P; Cocco, S; De Leonardis, E; Monasson, R

    2014-07-01

    The mean-field (MF) approximation offers a simple, fast way to infer direct interactions between elements in a network of correlated variables, a common, computationally challenging problem with practical applications in fields ranging from physics and biology to the social sciences. However, MF methods achieve their best performance with strong regularization, well beyond Bayesian expectations, an empirical fact that is poorly understood. In this work, we study the influence of pseudocount and L(2)-norm regularization schemes on the quality of inferred Ising or Potts interaction networks from correlation data within the MF approximation. We argue, based on the analysis of small systems, that the optimal value of the regularization strength remains finite even if the sampling noise tends to zero, in order to correct for systematic biases introduced by the MF approximation. Our claim is corroborated by extensive numerical studies of diverse model systems and by the analytical study of the m-component spin model for large but finite m. Additionally, we find that pseudocount regularization is robust against sampling noise and often outperforms L(2)-norm regularization, particularly when the underlying network of interactions is strongly heterogeneous. Much better performances are generally obtained for the Ising model than for the Potts model, for which only couplings incoming onto medium-frequency symbols are reliably inferred.

  13. Damage spreading at the corner-filling transition in the two-dimensional Ising model

    Science.gov (United States)

    Rubio Puzzo, M. Leticia; Albano, Ezequiel V.

    2007-01-01

    The propagation of damage on the square Ising lattice with a corner geometry is studied by means of Monte Carlo simulations. By imposing free boundary conditions at which competing boundary magnetic fields ± h are applied, the system undergoes a filling transition at a temperature Tf(h) lower than the Onsager critical temperature TC. The competing fields cause the formation of two magnetic domains with opposite orientation of the magnetization, separated by an interface that for T larger than Tf(h) (but Tinterface is localized either close to the corner where the magnetic field is positive or close to the opposite one, with the same probability. It is found that, just at T = Tf(h), the damage initially propagates along the interface of the competing domains, according to a power law given by D(t) \\propto t^{\\eta } . The value obtained for the dynamic exponent (η* = 0.89(1)) is in agreement with that corresponding to the wetting transition in the slit geometry (Abraham model) given by ηWT = 0.91(1). However, for later times the propagation crosses to a new regime such as η** = 0.40(2), which is due to the propagation of the damage into the bulk of the magnetic domains. This result can be understood as being due to the constraints imposed on the propagation of damage by the corner geometry of the system that cause healing at the corners where the interface is attached. The critical points for the damage-spreading transition (TD(h)) are evaluated by extrapolation to the thermodynamic limit by using a finite-size scaling approach. Considering error bars, an overlap between the filling and the damage-spreading transitions is found, such that Tf(h) = TD(h). The probability distribution of the damage average position P(l0D) and that of the interface between magnetic domains of different orientation P(l0) are evaluated and compared. It is found that, within the nonwet phase, the average position of the damage lies slightly shifted from the interface towards the side

  14. Experimental mathematics on the magnetic susceptibility of the square lattice Ising model

    Energy Technology Data Exchange (ETDEWEB)

    Boukraa, S [LPTHIRM and Departement d' Aeronautique, Universite de Blida (Algeria); Guttmann, A J; Jensen, I [ARC Centre of Excellence for Mathematics and Statistics of Complex Systems, Department of Mathematics and Statistics, University of Melbourne, Victoria 3010 (Australia); Hassani, S; Zenine, N [Centre de Recherche Nucleaire d' Alger, 2 Bd. Frantz Fanon, BP 399, 16000 Alger (Algeria); Maillard, J-M [LPTMC, Universite de Paris, Tour 24, 4eme etage, case 121, 4 Place Jussieu, 75252 Paris Cedex 05 (France); Nickel, B [Department of Physics, University of Guelph, Guelph, Ontario N1G 2W1 (Canada)], E-mail: boukraa@mail.univ-blida.dz, E-mail: tonyg@ms.unimelb.edu.au, E-mail: I.Jensen@ms.unimelb.edu.au, E-mail: maillard@lptmc.jussieu.fr, E-mail: maillard@lptl.jussieu.fr, E-mail: njzenine@yahoo.com

    2008-11-14

    We calculate very long low- and high-temperature series for the susceptibility {chi} of the square lattice Ising model as well as very long series for the five-particle contribution {chi}{sup (5)} and six-particle contribution {chi}{sup (6)}. These calculations have been made possible by the use of highly optimized polynomial time modular algorithms and a total of more than 150 000 CPU hours on computer clusters. The series for {chi} (low- and high-temperature regimes), {chi}{sup (5)} and {chi}{sup (6)} are now extended to 2000 terms. In addition, for {chi}{sup (5)}, 10 000 terms of the series are calculated modulo a single prime, and have been used to find the linear ODE satisfied by {chi}{sup (5)} modulo a prime. A diff-Pade analysis of the 2000 terms series for {chi}{sup (5)} and {chi}{sup (6)} confirms to a very high degree of confidence previous conjectures about the location and strength of the singularities of the n-particle components of the susceptibility, up to a small set of 'additional' singularities. The exponents at all the singularities of the Fuchsian linear ODE of {chi}{sup (5)} and the (as yet unknown) ODE of {chi}{sup (6)} are given: they are all rational numbers. We find the presence of singularities at w = 1/2 for the linear ODE of {chi}{sup (5)}, and w{sup 2} = 1/8 for the ODE of {chi}{sup (6)}, which are not singularities of the 'physical' {chi}{sup (5)} and {chi}{sup (6)}, that is to say the series solutions of the ODE's which are analytic at w = 0. Furthermore, analysis of the long series for {chi}{sup (5)} (and {chi}{sup (6)}) combined with the corresponding long series for the full susceptibility {chi} yields previously conjectured singularities in some {chi}{sup (n)}, n {>=} 7. The exponents at all these singularities are also seen to be rational numbers. We also present a mechanism of resummation of the logarithmic singularities of the {chi}{sup (n)} leading to the known power-law critical behaviour occurring in

  15. Finite-size scaling relations for a four-dimensional Ising model on Creutz cellular automatons

    Science.gov (United States)

    Merdan, Z.; Güzelsoy, E.

    2011-06-01

    The four-dimensional Ising model is simulated on Creutz cellular automatons using finite lattices with linear dimensions 4 ≤ L ≤ 8. The temperature variations and finite-size scaling plots of the specific heat and the Binder parameter verify the theoretically predicted expression near the infinite lattice critical temperature for 7, 14, and 21 independent simulations. Approximate values for the critical temperature of the infinite lattice of Tc(∞) = 6.6965(35), 6.6961(30), 6.6960(12), 6.6800(3), 6.6801(2), 6.6802(1) and 6.6925(22) (without the logarithmic factor), 6.6921(22) (without the logarithmic factor), 6.6909(2) (without the logarithmic factor), 6.6822(13) (with the logarithmic factor), 6.6819(11) (with the logarithmic factor), and 6.6808(8) (with the logarithmic factor) are obtained from the intersection points of the specific heat curves, the Binder parameter curves, and straight line fits of specific heat maxima for 7, 14, and 21 independent simulations, respectively. As the number of independent simulations increases, the results, 6.6802(1) and 6.6808(8), are in very good agreement with the results of a series expansion of Tc(∞), 6.6817(15) and 6.6802(2), the dynamic Monte Carlo value Tc(∞) = 6.6803(1), the cluster Monte Carlo value Tc(∞) = 6.680(1), and the Monte Carlo value using the Metropolis-Wolff cluster algorithm Tc(∞) = 6.6802632 ± 5 . 10-5. The average values calculated for the critical exponent of the specific heat are α =- 0.0402(15), - 0.0393(12), - 0.0391(11) with 7, 14, and 21 independent simulations, respectively. As the number of independent simulations increases, the result, α =- 0.0391(11), agrees with the series expansions result, α =- 0.12 ± 0.03 and the Monte Carlo result using the Metropolis-Wolff cluster algorithm, α ≥ 0 ± 0.04. However, α =- 0.0391(11) is inconsistent with the renormalization group prediction of α = 0.

  16. Quasi-additive estimates on the Hamiltonian for the one-dimensional long range Ising model

    Science.gov (United States)

    Littin, Jorge; Picco, Pierre

    2017-07-01

    In this work, we study the problem of getting quasi-additive bounds for the Hamiltonian of the long range Ising model, when the two-body interaction term decays proportionally to 1/d2 -α , α ∈(0,1 ) . We revisit the paper by Cassandro et al. [J. Math. Phys. 46, 053305 (2005)] where they extend to the case α ∈[0 ,ln3/ln2 -1 ) the result of the existence of a phase transition by using a Peierls argument given by Fröhlich and Spencer [Commun. Math. Phys. 84, 87-101 (1982)] for α =0 . The main arguments of Cassandro et al. [J. Math. Phys. 46, 053305 (2005)] are based in a quasi-additive decomposition of the Hamiltonian in terms of hierarchical structures called triangles and contours, which are related to the original definition of contours introduced by Fröhlich and Spencer [Commun. Math. Phys. 84, 87-101 (1982)]. In this work, we study the existence of a quasi-additive decomposition of the Hamiltonian in terms of the contours defined in the work of Cassandro et al. [J. Math. Phys. 46, 053305 (2005)]. The most relevant result obtained is Theorem 4.3 where we show that there is a quasi-additive decomposition for the Hamiltonian in terms of contours when α ∈[0,1 ) but not in terms of triangles. The fact that it cannot be a quasi-additive bound in terms of triangles lead to a very interesting maximization problem whose maximizer is related to a discrete Cantor set. As a consequence of the quasi-additive bounds, we prove that we can generalise the [Cassandro et al., J. Math. Phys. 46, 053305 (2005)] result, that is, a Peierls argument, to the whole interval α ∈[0,1 ) . We also state here the result of Cassandro et al. [Commun. Math. Phys. 327, 951-991 (2014)] about cluster expansions which implies that Theorem 2.4 that concerns interfaces and Theorem 2.5 that concerns n point truncated correlation functions in Cassandro et al. [Commun. Math. Phys. 327, 951-991 (2014)] are valid for all α ∈[0,1 ) instead of only α ∈[0 ,ln3/ln2 -1 ) .

  17. Simulation of the Ising model, memory for Bell states and generation of four-atom entangled states in cavity QED

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    A scheme is proposed to simulate the Ising model and preserve the maximum entangled states (Bell states) in cavity quantum electrodynamics (QED) driven by a classical field with large detuning. In the strong driving and large-detuning regime, the effective Hamiltonian of the system is the same as the standard Ising model, and the scheme can also make the initial four Bell states of two atoms at the maximum entanglement all the time. So it is a simple memory for the maximal entangled states. The system is insensitive to the cavity decay and the thermal field and more immune to decoherence. These advantages can warrant the experimental feasibility of the current scheme. Furthermore, the genuine four-atom entanglement may be acquired via two Bell states through one-step implementation on four two-level atoms in the strong-driven model, and when two Greenberger-Horne-Zeilinger (GHZ) states are prepared in our scheme, the entangled cluster state may be acquired easily. The success probability for the scheme is 1.

  18. Temperature effects on the dynamics of the 1-D transverse Ising model with four-spin interactions

    Science.gov (United States)

    Florencio, J.; de Alcantara Bonfim, O. F.

    2004-12-01

    The dynamics of one-dimensional quantum spin systems has been a long standing theoretical and experimental problem. Among them, the transverse Ising model with multi-spin interactions, regarded as one of the simplest with non-trivial dynamics, has attracted considerable interest in recent years. We investigate the temperature effects on the dynamics of the transverse Ising model with four-spin interactions. The model is relevant to the physics of poly(vinylidene fluoride-trifluoroethylene)[P(VDF-TrFE)] copolymers. We determine the time-dependent correlation function and spectral density for all temperatures for cases where the transverse field B is less, equal or greater than the four-spin coupling J. Our calculations were done with rings of up to 11 spins. However the results presented are also valid in the thermodynamic limit. We find that the time-dependent correlation function in general has oscillatory behavior when the transverse field is stronger than the coupling energy. On the other hand, when the field is weaker the real part of the time-dependent correlation function decreases monotonically at high enough temperatures. The temperature effects are best seen from the spectral density: at zero temperature the system can only absorb energy and, as the temperature is raised, the correlation functions keep memory of the zero-temperature quantum phases. Such feature persists up to the infinite temperature limit.

  19. Presence or absence of order by disorder in a highly frustrated region of the spin-1/2 Ising-Heisenberg model on triangulated Husimi lattices.

    Science.gov (United States)

    Strečka, Jozef; Ekiz, Cesur

    2015-05-01

    The geometrically frustrated spin-1/2 Ising-Heisenberg model on triangulated Husimi lattices is exactly solved by combining the generalized star-triangle transformation with the method of exact recursion relations. The ground-state and finite-temperature phase diagrams are rigorously calculated along with both sublattice magnetizations of the Ising and Heisenberg spins. It is evidenced that the Ising-Heisenberg model on triangulated Husimi lattices with two or three interconnected triangles-in-triangles units displays in a highly frustrated region a quantum disorder irrespective of temperature, whereas the same model on triangulated Husimi lattices with a greater connectivity of triangles-in-triangles units exhibits at low enough temperatures an outstanding quantum order due to the order-by-disorder mechanism. The quantum reduction of both sublattice magnetizations in the peculiar quantum ordered state gradually diminishes upon increasing the coordination number of the underlying Husimi lattice.

  20. Phase transitions of geometrically frustrated mixed spin-1/2 and spin-1 Ising-Heisenberg model on diamond-like decorated planar lattices

    Directory of Open Access Journals (Sweden)

    L. Gálisová

    2011-03-01

    Full Text Available Phase transitions of the mixed spin-1/2 and spin-1 Ising-Heisenberg model on several decorated planar lattices consisting of interconnected diamonds are investigated within the framework of the generalized decoration-iteration transformation. The main attention is paid to the systematic study of the finite-temperature phase diagrams in dependence on the lattice topology. The critical behaviour of the hybrid quantum-classical Ising-Heisenberg model is compared with the relevant behaviour of its semi-classical Ising analogue. It is shown that both models on diamond-like decorated planar lattices exhibit a striking critical behaviour including reentrant phase transitions. The higher the lattice coordination number is, the more pronounced reentrance may be detected.

  1. Ising spins on thin graphs

    CERN Document Server

    Baillie, C F; Kownacki, J P

    1994-01-01

    The Ising model on ``thin'' graphs (standard Feynman diagrams) displays several interesting properties. For ferromagnetic couplings there is a mean field phase transition at the corresponding Bethe lattice transition point. For antiferromagnetic couplings the replica trick gives some evidence for a spin glass phase. In this paper we investigate both the ferromagnetic and antiferromagnetic models with the aid of simulations. We confirm the Bethe lattice values of the critical points for the ferromagnetic model on \\phi^3 and \\phi^4 graphs and examine the putative spin glass phase in the antiferromagnetic model by looking at the overlap between replicas in a quenched ensemble of graphs. We also compare the Ising results with those for higher state Potts models and Ising models on ``fat'' graphs, such as those used in 2D gravity simulations.

  2. Behaviors of Phase Diagrams of an Ising Model on a Cayley Tree-Like Lattice: Rectangular Chandelier

    Science.gov (United States)

    Akin, Hasan; Uǧuz, Selman; Temir, Seyit

    2010-09-01

    In this work, we study an Ising model on a new lattice type which we called Rectangular Chandelier, with competing nearest-neighbor interactions J1, prolonged ternary interactions Jt and one-level next-nearest-neighbor quinary interactions Jl1(5). We obtain the phase diagrams of the Ising model related to Hamiltonian system give above on a Rectangular Chandelier. The phase diagrams are presented in the Hamiltonian 3-parameter space. To perform this study, an iterative scheme similar to that appearing in real space renormalization group frameworks is established. At vanishing temperature, the phase diagram is fully determined for all values and signs of J1, Jt and Jl1(5). At finite temperatures several interesting features are exhibited for typical values of -Jt/J1. For some values of -Jt/J1 and Jl1(5)/J1/J1, we determine the existince of multicritical Lifshitz points that are at non zero temperature, while it was stuck at zero temperature T for all systems with competing interactions, studied on the Cayley tree in the previous works.

  3. Dynamic phase transitions and dynamic phase diagrams of the Ising model on the Shastry-Sutherland lattice

    Energy Technology Data Exchange (ETDEWEB)

    Deviren, Şeyma Akkaya, E-mail: sadeviren@nevsehir.edu.tr [Department of Science Education, Education Faculty, Nevsehir Hacı Bektaş Veli University, 50300 Nevşehir (Turkey); Deviren, Bayram [Department of Physics, Nevsehir Hacı Bektaş Veli University, 50300 Nevsehir (Turkey)

    2016-03-15

    The dynamic phase transitions and dynamic phase diagrams are studied, within a mean-field approach, in the kinetic Ising model on the Shastry-Sutherland lattice under the presence of a time varying (sinusoidal) magnetic field by using the Glauber-type stochastic dynamics. The time-dependence behavior of order parameters and the behavior of average order parameters in a period, which is also called the dynamic order parameters, as a function of temperature, are investigated. Temperature dependence of the dynamic magnetizations, hysteresis loop areas and correlations are investigated in order to characterize the nature (first- or second-order) of the dynamic phase transitions as well as to obtain the dynamic phase transition temperatures. We present the dynamic phase diagrams in the magnetic field amplitude and temperature plane. The phase diagrams exhibit a dynamic tricritical point and reentrant phenomena. The phase diagrams also contain paramagnetic (P), Néel (N), Collinear (C) phases, two coexistence or mixed regions, (N+C) and (N+P), which strongly depend on interaction parameters. - Highlights: • Dynamic magnetization properties of spin-1/2 Ising model on SSL are investigated. • Dynamic magnetization, hysteresis loop area, and correlation have been calculated. • The dynamic phase diagrams are constructed in (T/|J|, h/|J|) plane. • The phase diagrams exhibit a dynamic tricritical point and reentrant phenomena.

  4. Pseudolikelihood decimation algorithm improving the inference of the interaction network in a general class of Ising models.

    Science.gov (United States)

    Decelle, Aurélien; Ricci-Tersenghi, Federico

    2014-02-21

    In this Letter we propose a new method to infer the topology of the interaction network in pairwise models with Ising variables. By using the pseudolikelihood method (PLM) at high temperature, it is generally possible to distinguish between zero and nonzero couplings because a clear gap separate the two groups. However at lower temperatures the PLM is much less effective and the result depends on subjective choices, such as the value of the ℓ1 regularizer and that of the threshold to separate nonzero couplings from null ones. We introduce a decimation procedure based on the PLM that recursively sets to zero the less significant couplings, until the variation of the pseudolikelihood signals that relevant couplings are being removed. The new method is fully automated and does not require any subjective choice by the user. Numerical tests have been performed on a wide class of Ising models, having different topologies (from random graphs to finite dimensional lattices) and different couplings (both diluted ferromagnets in a field and spin glasses). These numerical results show that the new algorithm performs better than standard PLM.

  5. Observation of flat band for terahertz coupled plasmon in metallic kagom\\'e lattice

    CERN Document Server

    Nakata, Yosuke; Nakanishi, Toshihiro; Kitano, Masao

    2012-01-01

    We study the dispersion relation of a metamaterial composed of metallic discs and bars arranged to have kagom\\'{e} symmetry and find that a plasmonic flat band is formed by the topological nature of the kagom\\'{e} lattice. To confirm the flat band formation, we fabricate the metamaterial and make transmission measurements in the terahertz regime. Two bands formed by transmission minima that depend on the polarization of the incident terahertz beams are observed. One of the bands corresponds to the flat band as confirmed by the fact that the resonant frequency is almost independent of the incident angle.

  6. Series Expansions for Frustrated Quantum Ising Magnets

    Science.gov (United States)

    Gelfand, M. P.; Priour, D. J.; Sondhi, S. L.

    2000-03-01

    We have computed the phase diagram of a frustrated Ising ladder in a transverse field via the Wolff Monte Carlo Cluster algorithm and by Pad'e Analysis of a series for the excitation spectrum about the large transverse field limit. A comparison of the two methods suggests that analysis of the perturbation series is a viable method for obtaining the phase diagrams of such systems even in cases, such as this one , where there is no phase transition down to arbitrarily small values of the transverse field. We will also discuss the application of the series technique to two dimensional systems of greater experimental interest, such as on the Kagome lattice which is also believed to realize a cooperative paramagnet at small transverse fields.

  7. Quantum spin liquid in a breathing kagome lattice

    Science.gov (United States)

    Schaffer, Robert; Huh, Yejin; Hwang, Kyusung; Kim, Yong Baek

    2017-02-01

    Motivated by recent experiments on the vanadium oxyfluoride material DQVOF, we examine possible spin liquid phases on a breathing kagome lattice of S =1 /2 spins. By performing a projective symmetry group analysis, we determine the possible phases for both fermionic and bosonic Z2 spin liquids on this lattice, and establish the correspondence between the two. The nature of the ground state of the Heisenberg model on the isotropic kagome lattice is a hotly debated topic, with both Z2 and U(1) spin liquids argued to be plausible ground states. Using variational Monte Carlo techniques, we show that a gapped Z2 spin liquid emerges as the clear ground state in the presence of this breathing anisotropy. Our results suggest that the breathing anisotropy helps to stabilize this spin liquid ground state, which may aid us in understanding the results of experiments and help to direct future numerical studies on these systems.

  8. Anomalous Hall Effect in a Kagome Ferromagnet

    Science.gov (United States)

    Ye, Linda; Wicker, Christina; Suzuki, Takehito; Checkelsky, Joseph; Joseph Checkelsky Team

    The ferromagnetic kagome lattice is theoretically known to possess topological band structures. We have synthesized large single crystals of a kagome ferromagnet Fe3Sn2 which orders ferromagnetically well above room temperature. We have studied the electrical and magnetic properties of these crystals over a broad temperature and magnetic field range. Both the scaling relation of anomalous Hall effect and anisotropic magnetic susceptibility show that the ferromagnetism of Fe3Sn2 is unconventional. We discuss these results in the context of magnetism in kagome systems and relevance to the predicted topological properties in this class of compounds. This research is supported by DMR-1231319.

  9. Equilibrium and Non-equilibrium Ising Models by Means of PCA

    Science.gov (United States)

    Lancia, Carlo; Scoppola, Benedetto

    2013-11-01

    We propose a unified approach to reversible and irreversible pca dynamics, and we show that in the case of 1D and 2D nearest neighbor Ising systems with periodic boundary conditions we are able to compute the stationary measure of the dynamics also when the latter is irreversible. We also show how, according to (P. Dai Pra et al. in J. Stat. Phys. 149(4):722-737, 2012), the stationary measure is very close to the Gibbs for a suitable choice of the parameters of the pca dynamics, both in the reversible and in the irreversible cases. We discuss some numerical aspects regarding this topic, including a possible parallel implementation.

  10. Suzuki-Trotter decomposition and renormalization of a transverse-field Ising model in two dimensions

    Science.gov (United States)

    Dudziński, M.; Sznajd, J.

    1997-06-01

    The combined Suzuki-Trotter decomposition and Niemeijer-van Leuween real-space renormalization-group techniques are used to study the critical properties of a two-dimensional Ising system with a transverse field. The inverse critical temperature as a function of the external field and the temperature dependence of the transverse component of the magnetization are found. It is also shown that any real-space renormalization-group procedure based on the simple generalization of the Niemeijer-van Leeuwen majority rule for one of the components of the total-cell spin does not preserve the symmetry of the quantum spin space.

  11. Finding and proving the exact ground state of a generalized Ising model by convex optimization and MAX-SAT

    CERN Document Server

    Huang, Wenxuan; Dacek, Stephen; Rong, Ziqin; Urban, Alexander; Cao, Shan; Luo, Chuan; Ceder, Gerbrand

    2016-01-01

    Lattice models, also known as generalized Ising models or cluster expansions, are widely used in many areas of science and are routinely applied to alloy thermodynamics, solid-solid phase transitions, magnetic and thermal properties of solids, and fluid mechanics, among others. However, the problem of finding the true global ground state of a lattice model, which is essential for all of the aforementioned applications, has remained unresolved, with only a limited number of results for highly simplified systems known. In this article, we present the first general algorithm to find the exact ground states of complex lattice models and to prove their global optimality, resolving this fundamental problem in condensed matter and materials theory. We transform the infinite-discrete-optimization problem into a pair of combinatorial optimization (MAX-SAT) and non-smooth convex optimization (MAX-MIN) problems, which provide upper and lower bounds on the ground state energy respectively. By systematically converging th...

  12. Damage spreading at the corner-filling transition in the two-dimensional Ising model

    Energy Technology Data Exchange (ETDEWEB)

    Rubio Puzzo, M Leticia; Albano, Ezequiel V [Instituto de Investigaciones Fisicoquimicas Teoricas y Aplicadas (INIFTA), Facultad de Ciencias Exactas, UNLP, CONICET, Casilla de Correo 16, Sucursal 4 (1900) La Plata (Argentina)

    2007-01-17

    The propagation of damage on the square Ising lattice with a corner geometry is studied by means of Monte Carlo simulations. By imposing free boundary conditions at which competing boundary magnetic fields {+-} h are applied, the system undergoes a filling transition at a temperature T{sub f}(h) lower than the Onsager critical temperature T{sub C}. The competing fields cause the formation of two magnetic domains with opposite orientation of the magnetization, separated by an interface that for T larger than T{sub f}(h) (but Tmodel) given by {eta}{sup WT} = 0.91(1). However, for later times the propagation crosses to a new regime such as {eta}** = 0.40(2), which is due to the propagation of the damage into the bulk of the magnetic domains. This result can be understood as being due to the constraints imposed on the propagation of damage by the corner geometry of the system that cause healing at the corners where the interface is attached. The critical points for the damage-spreading transition (T{sub D}(h)) are evaluated by extrapolation to the thermodynamic limit by using a finite-size scaling approach. Considering error bars, an overlap between the filling and the damage-spreading transitions is found, such that T{sub f}(h) = T{sub D}(h). The probability distribution of the damage average position P(l{sub 0}{sup D}) and

  13. An effective correlated mean-field theory applied in the spin-1/2 Ising ferromagnetic model

    Energy Technology Data Exchange (ETDEWEB)

    Roberto Viana, J.; Salmon, Octávio R. [Universidade Federal do Amazonas – UFAM, Manaus 69077-000, AM (Brazil); Ricardo de Sousa, J. [Universidade Federal do Amazonas – UFAM, Manaus 69077-000, AM (Brazil); National Institute of Science and Technology for Complex Systems, Universidade Federal do Amazonas, 3000, Japiim, 69077-000 Manaus, AM (Brazil); Neto, Minos A.; Padilha, Igor T. [Universidade Federal do Amazonas – UFAM, Manaus 69077-000, AM (Brazil)

    2014-11-15

    We developed a new treatment for mean-field theory applied in spins systems, denominated effective correlated mean-field (ECMF). We apply this theory to study the spin-1/2 Ising ferromagnetic model with nearest-neighbor interactions on a square lattice. We use clusters of finite sizes and study the criticality of the ferromagnetic system, where we obtain a convergence of critical temperature for the value k{sub B}T{sub c}/J≃2.27905±0.00141. Also the behavior of magnetic and thermodynamic properties, using the condition of minimum energy of the physical system is obtained. - Highlights: • We developed spin models to study real magnetic systems. • We study the thermodynamic and magnetic properties of the ferromagnetism. • We enhanced a mean-field theory applied in spins models.

  14. A generalized Ising model for studying alloy evolution under irradiation and its use in kinetic Monte Carlo simulations

    Science.gov (United States)

    Huang, Chen-Hsi; Marian, Jaime

    2016-10-01

    We derive an Ising Hamiltonian for kinetic simulations involving interstitial and vacancy defects in binary alloys. Our model, which we term ‘ABVI’, incorporates solute transport by both interstitial defects and vacancies into a mathematically-consistent framework, and thus represents a generalization to the widely-used ABV model for alloy evolution simulations. The Hamiltonian captures the three possible interstitial configurations in a binary alloy: A-A, A-B, and B-B, which makes it particularly useful for irradiation damage simulations. All the constants of the Hamiltonian are expressed in terms of bond energies that can be computed using first-principles calculations. We implement our ABVI model in kinetic Monte Carlo simulations and perform a verification exercise by comparing our results to published irradiation damage simulations in simple binary systems with Frenkel pair defect production and several microstructural scenarios, with matching agreement found.

  15. Finding and proving the exact ground state of a generalized Ising model by convex optimization and MAX-SAT

    Science.gov (United States)

    Huang, Wenxuan; Kitchaev, Daniil A.; Dacek, Stephen T.; Rong, Ziqin; Urban, Alexander; Cao, Shan; Luo, Chuan; Ceder, Gerbrand

    2016-10-01

    Lattice models, also known as generalized Ising models or cluster expansions, are widely used in many areas of science and are routinely applied to the study of alloy thermodynamics, solid-solid phase transitions, magnetic and thermal properties of solids, fluid mechanics, and others. However, the problem of finding and proving the global ground state of a lattice model, which is essential for all of the aforementioned applications, has remained unresolved for relatively complex practical systems, with only a limited number of results for highly simplified systems known. In this paper, we present a practical and general algorithm that provides a provable periodically constrained ground state of a complex lattice model up to a given unit cell size and in many cases is able to prove global optimality over all other choices of unit cell. We transform the infinite-discrete-optimization problem into a pair of combinatorial optimization (MAX-SAT) and nonsmooth convex optimization (MAX-MIN) problems, which provide upper and lower bounds on the ground state energy, respectively. By systematically converging these bounds to each other, we may find and prove the exact ground state of realistic Hamiltonians whose exact solutions are difficult, if not impossible, to obtain via traditional methods. Considering that currently such practical Hamiltonians are solved using simulated annealing and genetic algorithms that are often unable to find the true global energy minimum and inherently cannot prove the optimality of their result, our paper opens the door to resolving longstanding uncertainties in lattice models of physical phenomena. An implementation of the algorithm is available at https://github.com/dkitch/maxsat-ising.

  16. Two-dimensional Kagome photonic bandgap waveguide

    DEFF Research Database (Denmark)

    Nielsen, Jens Bo; Søndergaard, Thomas; Libori, Stig E. Barkou;

    2000-01-01

    The transverse-magnetic photonic-bandgap-guidance properties are investigated for a planar two-dimensional (2-D) Kagome waveguide configuration using a full-vectorial plane-wave-expansion method. Single-moded well-localized low-index guided modes are found. The localization of the optical modes...... is investigated with respect to the width of the 2-D Kagome waveguide, and the number of modes existing for specific frequencies and waveguide widths is mapped out....

  17. Topological phase transition in a gravity description of the transverse-field Ising model in one dimension

    CERN Document Server

    Kim, Ki-Seok

    2016-01-01

    We develop a gravity reformulation for a topological phase transition of the Kitaev superconductor model in one dimension. Applying the Wilson's renormalization group procedure repeatedly, we find an effective theory with a renormalized coupling function, where the repetition index of the renormalization group transformation is identified with an extra dimension. Solving the renormalization group equation, we obtain an effective interaction vertex as a function of the extra dimension. The topological quantum phase transition is encoded into the gravity description as follows: First, the inter-site correlation (hopping and pairing) strength of spinless fermions given by a ferromagnetic coupling constant in the transverse-field Ising model is renormalized to vanish in a topologically trivial p-wave superconducting state, adiabatically connected to a trivial insulating behavior. Second, the inter-site correlation strength does not evolve at a quantum critical point, giving rise to a conformal field theory that d...

  18. Monte-Carlo Simulations of Spin-Crossover Phenomena Based on a Vibronic Ising-like Model with Realistic Parameters

    CERN Document Server

    Ye, Hong-zhou; Jiang, Hong

    2014-01-01

    Materials with spin-crossover (SCO) properties hold great potentials in information storage and therefore have received a lot of concerns in the recent decades. The hysteresis phenomena accompanying SCO is attributed to the intermolecular cooperativity whose underlying mechanism may have a vibronic origin. In this work, a new vibronic Ising-like model in which the elastic coupling between SCO centers is included by considering harmonic stretching and bending (SAB) interactions is proposed and solved by Monte Carlo simulations. The key parameters in the new model, $k_1$ and $k_2$, corresponding to the elastic constant of the stretching and bending mode, respectively, can be directly related to the macroscopic bulk and shear modulus of the material in study, which can be readily estimated either based on experimental measurements or first-principles calculations. The convergence issue in the MC simulations of the thermal hysteresis has been carefully checked, and it was found that the stable hysteresis loop can...

  19. LETTER TO THE EDITOR: Coarsening in the 1D Ising model evolving with Swendsen - Wang dynamics: an unusual scaling

    Science.gov (United States)

    Derrida, Bernard; Hakim, Vincent

    1996-12-01

    We consider a simple model of domain growth: the zero-temperature 1D Ising model evolving according to the Swendsen - Wang dynamics. We find that in the long-time limit, the pair correlation function scales with a characteristic length increasing as the square of the average domain size. In that limit, a few large domains occupy almost all the space with many small domains between them. In contrast to the usual picture of coarsening, the average domain size here is not a characteristic length of the growth problem. Instead, one finds a power-law distribution for the sizes of large domains with a cut-off at a length which grows as the square of the average size of the domains.

  20. Study of BaxSr1-xTiO3 thin films using transverse-field Ising model

    Institute of Scientific and Technical Information of China (English)

    Tao Yong-Mei; Jiang Qing

    2004-01-01

    In this paper, the effects of doping on the thermodynamic properties of BaxSr1-xTiO3 (BST) thin film are investigated, based on the transverse-field Ising model (TIM) within the framework of mean field theory. We apply the double-peak distribution model of related parameters to mimic doping. The lattice expansion arising from doping with large Ba2+ was also taken into account. We concentrate on the doping concentration dependence of peak temperature (Tm), spontaneous polarization and dielectric susceptibility. It is found that the doping concentration has great influence on the dielectric properties and phase transition properties of BST thin films. We also discuss the quantum effect arising from doping.

  1. Criticality governed by the stable renormalization fixed point of the Ising model in the hierarchical small-world network.

    Science.gov (United States)

    Nogawa, Tomoaki; Hasegawa, Takehisa; Nemoto, Koji

    2012-09-01

    We study the Ising model in a hierarchical small-world network by renormalization group analysis and find a phase transition between an ordered phase and a critical phase, which is driven by the coupling strength of the shortcut edges. Unlike ordinary phase transitions, which are related to unstable renormalization fixed points (FPs), the singularity in the ordered phase of the present model is governed by the FP that coincides with the stable FP of the ordered phase. The weak stability of the FP yields peculiar criticalities, including logarithmic behavior. On the other hand, the critical phase is related to a nontrivial FP, which depends on the coupling strength and is continuously connected to the ordered FP at the transition point. We show that this continuity indicates the existence of a finite correlation-length-like quantity inside the critical phase, which diverges upon approaching the transition point.

  2. The effect of uniaxial crystal-field anisotropy on magnetic properties of the superexchange antiferromagnetic Ising model

    Directory of Open Access Journals (Sweden)

    L.Canová

    2006-01-01

    Full Text Available The generalized Fisher super-exchange antiferromagnetic model with uniaxial crystal-field anisotropy is exactly investigated using an extended mapping technique. An exact relation between partition function of the studied system and that of the standard zero-field spin-1/2 Ising model on the corresponding lattice is obtained applying the decoration-iteration transformation. Consequently, exact results for all physical quantities are derived for arbitrary spin values S of decorating atoms. Particular attention is paid to the investigation of the effect of crystal-field anisotropy and external longitudinal magnetic field on magnetic properties of the system under investigation. The most interesting numerical results for ground-state and finite-temperature phase diagrams, thermal dependences of the sublattice magnetization and other thermodynamic quantities are discussed.

  3. DMRG studies of the frustrated kagome antiferromagnets and the application to volborthite

    Science.gov (United States)

    Gong, Shou-Shu; Sheng, D. N.; Yang, Kun

    Motivated by the recent magnetization measurements on the high-quality single crystals of the kagome antiferromagnet volborthite, we study the ground state and magnetization properties of two kagome models proposed from the electronic structure simulations, which treat the volborthite as either the coupled trimers or the coupled frustrated chains on the kagome lattice. We study the models using density-matrix renormalization group on the cylinder geometry with the system width up to 4 legs. We find a quantum phase diagram of the models with changing couplings, and identify the magnetic properties of each phase. In the antiferromagnetic phases, we also study the magnetization curve and the different phases in the magnetic field. Finally, we compare the magetization properties of the models with the experimental observations of volborthite. NSF DMR-1157490, DMR-1408560, and the State of Florida.

  4. Magnetic Properties of Transverse Ising Model under a Time Oscillating Longitudinal Field

    Institute of Scientific and Technical Information of China (English)

    SHI Xiao-Ling; WANG Li; WEI Guo-Zhu

    2011-01-01

    A transverse Ising spin system, in the presence of time-dependent longitudinal field, is studied by the effective-field theory (EFT). The effective-field equations of motion of the average magnetization are given for the simple cubic lattice (Z = 6) and the honeycomb lattice (Z = 3). The Liapunov exponent λ is calculated for discussing the stability of the magnetization and it is used to determine the phase boundary. The dynamic phase transition diagrams in ho/ZJ - Γ/ZJ plane and in ho/ZJ - T/ZJ plane have been drawn, and there is no dynamical tricritical point on the dynamic phase transition boundary. The effect of the thermal fluctuations upon the dynamic phase boundary has been discussed.

  5. Size reduction of the transfer matrix of two-dimensional Ising and Potts models

    Directory of Open Access Journals (Sweden)

    M. Ghaemi

    2003-12-01

    Full Text Available  A new algebraic method is developed to reduce the size of the transfer matrix of Ising and three-state Potts ferromagnets on strips of width r sites of square and triangular lattices. This size reduction has been set up in such a way that the maximum eigenvalues of both the reduced and the original transfer matrices became exactly the same. In this method we write the original transfer matrix in a special blocked form in such a way that the sums of row elements of a block of the original transfer matrix be the same. The reduced matrix is obtained by replacing each block of the original transfer matrix with the sum of the elements of one of its rows. Our method results in significant matrix size reduction which is a crucial factor in determining the maximum eigenvalue.

  6. Destruction of first-order phase transition in a random-field Ising model

    Energy Technology Data Exchange (ETDEWEB)

    Crokidakis, Nuno; Nobre, Fernando D [Centro Brasileiro de Pesquisas Fisicas, Rua Xavier Sigaud 150, 22290-180, Rio de Janeiro-RJ (Brazil)], E-mail: nuno@if.uff.br, E-mail: fdnobre@cbpf.br

    2008-04-09

    The phase transitions that occur in an infinite-range-interaction Ising ferromagnet in the presence of a double Gaussian random magnetic field are analyzed. Such random fields are defined as a superposition of two Gaussian distributions, presenting the same width {sigma}. It is argued that this distribution is more appropriate for a theoretical description of real systems than other simpler cases, i.e. the bimodal ({sigma} = 0) and single Gaussian distributions. It is shown that a low-temperature first-order phase transition may be destroyed for increasing values of {sigma}, similarly to what happens in the compound Fe{sub x}Mg{sub 1-x}Cl{sub 2}, whose finite-temperature first-order phase transition is presumably destroyed by an increase in the field randomness.

  7. The democracy ochlocracy dictatorship transition in the Sznajd model and in the Ising model

    Science.gov (United States)

    Schneider, Johannes J.; Hirtreiter, Christian

    2005-08-01

    Since its introduction in 2000, the Sznajd model has been assumed to simulate a democratic community with two parties. The main flaw in this model is that a Sznajd system freezes in the long term in a non-democratic state, which can be either a dictatorship or a stalemate configuration. Here we show that the Sznajd model has better to be considered as a transition model, transferring a democratic system already at the beginning of a simulation via an ochlocratic scenario, i.e., a regime in which several mobs rule, to a dictatorship, thus reproducing the corresponding Aristotelian theory.

  8. Partition function for the two-dimensional square lattice Ising model in a non-zero magnetic field-A heuristic analysis

    OpenAIRE

    2008-01-01

    The exact partition function of the two-dimensional nearest neighbour Ising model pertaining to square lattices is derived for N sites in the case of a non-vanishing magnetic field.When the magnetic field is zero,the partition functions estimated from the present analysis are identical with those arising from Onsager's exact solution.

  9. Phase Diagrams, Criticality, and Local Properties of Spin Glasses and Random-Field Ising Models from Renormalization - Calculations.

    Science.gov (United States)

    Hartford, Edward John

    This position-space renormalization-group study focuses on two systems with quenched disorder: the Ising spin glass and the asymmetric random-field Ising model. We have employed the Migdal-Kadanoff approach to determine local recursion relations and have retained the full correlated probability distribution of interactions and fields at each iteration in a series of histograms. We find an equilibrium spin-glass phase in three dimensions, but not in two. The spin glass is characterized by a distribution of effective interactions that broadens under iteration, signaling both the long-range order of the phase and the importance of competing interactions on all length scales. We have introduced a method to calculate the distribution of local properties by differentiating the free energy with respect to a particular magnetic field or interaction. Within the spin-glass phase, the nearest neighbor correlation ranges from negative one to one, showing the strong correlations and the local variation within the phase. The spin-glass-to-paramagnet phase transition is second order, with a smooth specific heat indicated by a negative critical exponent alpha. The multicritical point separating the spin-glass, paramagnetic, and ferromagnetic phases lies along the Nishimori line and also has a nondivergent specific heat. When the system undergoes quenched dilution, the resulting critical and multicritical behaviors are identical to those of the undiluted system. Even the addition of an infinitesimal magnetic field destroys the long-range spin-glass order; however, the characteristic broadening of the distribution continues for several iterations for small fields and low temperatures, suggesting the persistence of sizable spin-glass domains. Our study of the asymmetric random-field Ising model is motivated by recent experiments on phase transitions in porous media and mean-field treatments, which suggest that new critical behavior could occur when the distribution of fields is

  10. Magnetic properties and interface delocalization in the three-dimensional Ising model with defect-plane amorphization

    Science.gov (United States)

    Benyoussef, A.; El Amraoui, Y.; El Kenz, A.; Kaneyoshi, T.

    1994-02-01

    Magnetic properties and interface delocalization of the spin-1/2 Ising model on a cubic lattice with an amorphized defect plane that divides the system into two semi-infinite ones are investigated by the use of the effective-field theory. The global phase diagrams, which represent the connection between amorphized defect-plane order and wetting transitions (from partial to complete wetting), are given in the case of two equivalent semi-infinite systems (the same coupling) and in the case of different semi-infinite systems. The influence of the amorphization in these global phase diagrams is also studied. Moreover, magnetic properties which illustrate some interesting behavior for the amorphized systems are investigated.

  11. Monte Carlo Simulation of 3-dimensional Ising Model%三维Ising模型的蒙特卡罗模拟

    Institute of Scientific and Technical Information of China (English)

    黄纯青; 邓绍军

    2009-01-01

    采用蒙特卡罗(Monte Cado)重点抽样法对三维Ising模型进行计算机模拟,测量无外磁场时三维Ising模型中自旋键链的能量、磁化强度、比热及磁化率的统计平均值与标准误差(不确定度).结果表明,三维Ising模型在无外磁场时存在自发磁化现象,铁磁→非铁磁相变临界点在J/(kBTc=0.222 0,或居里温度Tc=4.500 0处.并研究存在外磁场时上述物理量随温度与外磁场的变化规律,给出物理解释.%A 3-dimensional Ising model is simulated with Monte Carlo importance sampling method. Statistical values of energy, strength of magnetization, specific heat and rate of magnetization of spin links as well as their standard errors (uncertainties) are measured. 3-dimensional Ising model shows spontaneous magnetization with no exterior magnetic field. Critical point of phase transformation is at J/( k_BT_c ) = 0.222 0 or T_c = 4.500 0. Phase transformation at high temperature disappears with exterior magnetic field. Relationship between physical quantities, temperature and exterior magnetic field is investigated and analyzed.

  12. Variational perturbation and extended Plefka approaches to dynamics on random networks: the case of the kinetic Ising model

    Science.gov (United States)

    Bachschmid-Romano, L.; Battistin, C.; Opper, M.; Roudi, Y.

    2016-10-01

    We describe and analyze some novel approaches for studying the dynamics of Ising spin glass models. We first briefly consider the variational approach based on minimizing the Kullback-Leibler divergence between independent trajectories and the real ones and note that this approach only coincides with the mean field equations from the saddle point approximation to the generating functional when the dynamics is defined through a logistic link function, which is the case for the kinetic Ising model with parallel update. We then spend the rest of the paper developing two ways of going beyond the saddle point approximation to the generating functional. In the first one, we develop a variational perturbative approximation to the generating functional by expanding the action around a quadratic function of the local fields and conjugate local fields whose parameters are optimized. We derive analytical expressions for the optimal parameters and show that when the optimization is suitably restricted, we recover the mean field equations that are exact for the fully asymmetric random couplings (Mézard and Sakellariou 2011 J. Stat. Mech. 2011 L07001). However, without this restriction the results are different. We also describe an extended Plefka expansion in which in addition to the magnetization, we also fix the correlation and response functions. Finally, we numerically study the performance of these approximations for Sherrington-Kirkpatrick type couplings for various coupling strengths and the degrees of coupling symmetry, for both temporally constant but random, as well as time varying external fields. We show that the dynamical equations derived from the extended Plefka expansion outperform the others in all regimes, although it is computationally more demanding. The unconstrained variational approach does not perform well in the small coupling regime, while it approaches dynamical TAP equations of (Roudi and Hertz 2011 J. Stat. Mech. 2011 P03031) for strong couplings.

  13. CUDA programs for GPU computing of Swendsen-Wang multi-cluster spin flip algorithm: 2D and 3D Ising, Potts, and XY models

    CERN Document Server

    Komura, Yukihiro

    2014-01-01

    We present sample CUDA programs for the GPU computing of the Swendsen-Wang multi-cluster spin flip algorithm. We deal with the classical spin models; the Ising model, the $q$-state Potts model, and the classical XY model. As for the lattice, both the 2D (square) lattice and the 3D (simple cubic) lattice are treated. We already reported the idea of the GPU implementation for 2D models [Comput. Phys. Commun. 183 (2012) 1155-1161]. We here explain the details of sample programs, and discuss the performance of the present GPU implementation for the 3D Ising and XY models. We also show the calculated results of the moment ratio for these models, and discuss phase transitions.

  14. Monte Carlo simulations of the HP model (the "Ising model" of protein folding)

    Science.gov (United States)

    Li, Ying Wai; Wüst, Thomas; Landau, David P.

    2011-09-01

    Using Wang-Landau sampling with suitable Monte Carlo trial moves (pull moves and bond-rebridging moves combined) we have determined the density of states and thermodynamic properties for a short sequence of the HP protein model. For free chains these proteins are known to first undergo a collapse "transition" to a globule state followed by a second "transition" into a native state. When placed in the proximity of an attractive surface, there is a competition between surface adsorption and folding that leads to an intriguing sequence of "transitions". These transitions depend upon the relative interaction strengths and are largely inaccessible to "standard" Monte Carlo methods.

  15. Short-time critical dynamics of damage spreading in the two-dimensional Ising model

    Science.gov (United States)

    Rubio Puzzo, M. Leticia; Albano, Ezequiel V.

    2010-05-01

    The short-time critical dynamics of propagation of damage in the Ising ferromagnet in two dimensions is studied by means of Monte Carlo simulations. Starting with equilibrium configurations at T=∞ and magnetization M=0 , an initial damage is created by flipping a small amount of spins in one of the two replicas studied. In this way, the initial damage is proportional to the initial magnetization M0 in one of the configurations upon quenching the system at TC , the Onsager critical temperature of the ferromagnetic-paramagnetic transition. It is found that, at short times, the damage increases with an exponent θD=1.915(3) , which is much larger than the exponent θ=0.197 characteristic of the initial increase of the magnetization M(t) . Also, an epidemic study was performed. It is found that the average distance from the origin of the epidemic (⟨R2(t)⟩) grows with an exponent z∗≈η≈1.9 , which is the same, within error bars, as the exponent θD . However, the survival probability of the epidemics reaches a plateau so that δ=0 . On the other hand, by quenching the system to lower temperatures one observes the critical spreading of the damage at TD≃0.51TC , where all the measured observables exhibit power laws with exponents θD=1.026(3) , δ=0.133(1) , and z∗=1.74(3) .

  16. Study of the dynamical approach to the interface localization delocalization transition of the confined Ising model

    Science.gov (United States)

    Albano, Ezequiel V.; DeVirgiliis, Andres; Müller, Marcus; Binder, Kurt

    2004-06-01

    Confined magnetic Ising films in a L × D geometry (L \\ll D ), with short-range competing magnetic fields (h) acting at opposite walls along the D-direction, exhibit a slightly rounded localization-delocalization transition of the interface between domains of different orientations that runs parallel to the walls. This transition is the precursor of a wetting transition that occurs in the limit of infinite film thickness (L \\to \\infty ) at the critical curve Tw(h). For TTw(h)) such an interface is bounded (unbounded) to the walls, while right at Tw(h) the interface is freely fluctuating around the centre of the film. Starting from disordered configurations, corresponding to T=\\infty , we quench to the wetting critical temperature and study the dynamics of the approach to the stationary regime by means of extensive Monte Carlo simulations. It is found that for all layers parallel to the wall (rows), the row magnetizations exhibit a peak at a time \\tau _{\\max } \\propto L^{2} and subsequently relax to the stationary, equilibrium behaviour. The characteristic time for such a relaxation scales as \\tau_{\\mathrm {R}} \\propto L^{4} , as expected from theoretical arguments, that are discussed in detail.

  17. Many-body localization in Ising models with random long-range interactions

    Science.gov (United States)

    Li, Haoyuan; Wang, Jia; Liu, Xia-Ji; Hu, Hui

    2016-12-01

    We theoretically investigate the many-body localization phase transition in a one-dimensional Ising spin chain with random long-range spin-spin interactions, Vi j∝|i-j |-α , where the exponent of the interaction range α can be tuned from zero to infinitely large. By using exact diagonalization, we calculate the half-chain entanglement entropy and the energy spectral statistics and use them to characterize the phase transition towards the many-body localization phase at infinite temperature and at sufficiently large disorder strength. We perform finite-size scaling to extract the critical disorder strength and the critical exponent of the divergent localization length. With increasing α , the critical exponent experiences a sharp increase at about αc≃1.2 and then gradually decreases to a value found earlier in a disordered short-ranged interacting spin chain. For α localized and the increase in the disorder strength may drive a transition between two many-body localized phases. In contrast, for α >αc , the transition is from a thermalized phase to the many-body localization phase. Our predictions could be experimentally tested with an ion-trap quantum emulator with programmable random long-range interactions, or with randomly distributed Rydberg atoms or polar molecules in lattices.

  18. Temperature driven quenches in the Ising model: appearance of negative Rényi mutual information

    Science.gov (United States)

    Kormos, Márton; Zimborás, Zoltán

    2017-06-01

    We study the dynamics of the transverse field Ising chain after a local quench in which two independently thermalised chains are joined together and are left to evolve unitarily. In the emerging non-equilibrium steady state the Rényi mutual information with different indices are calculated between two adjacent segments of the chain, and are found to scale logarithmically in the subsystem size. Surprisingly, for Rényi indices α>2 we find cases where the prefactor of the logarithmic dependence is negative. The fact that the naively defined Rényi mutual information might be negative has been pointed out before, however, we provide the first example for this scenario in a realistic many-body setup. Our numerical and analytical results indicate that in this setup it can be negative for any index α>2 while it is always positive for α2 the calculated prefactors show some universal features: for example, the same prefactor is also shown to govern the logarithmic time dependence of the Rényi mutual information before the system relaxes locally to the steady state. In particular, it can decrease in the non-equilibrium evolution after the quench.

  19. Floquet topological phase transitions and chiral edge states in a kagome lattice

    Energy Technology Data Exchange (ETDEWEB)

    He, Chaocheng; Zhang, Zhiyong, E-mail: zyzhang@nju.edu.cn

    2014-09-05

    The Floquet topological phases and chiral edge states in a kagome lattice under a circularly-polarized driving field are studied. In the off-resonant case, the system exhibits the similar character as the kagome lattice model with staggered magnetic fluxes, but the total band width is damped in oscillation. In the on-resonant case, the degeneracy splitting at the Γ point does not always result in a gap. The positions of the other two gaps are influenced by the flat band. With the field intensity increased, these two gaps undergo closing-then-reopening processes, accompanied with the changing of the winding numbers. - Highlights: • A kagome lattice under a circularly-polarized driving field is studied. • The band structures and chiral edge states are studied via exact Floquet method. • Various modifications of the Floquet band structure are found. • Floquet topological phase transitions appear in both off- and on-resonant cases.

  20. Magnetic properties and concurrence for fluid {sup 3}He on kagome lattice

    Energy Technology Data Exchange (ETDEWEB)

    Ananikian, N. S., E-mail: ananik@yerphi.am; Ananikian, L. N. [A.I. Alikhanyan National Science Laboratory (Armenia); Lazaryan, H. A. [Yerevan State University (Armenia)

    2012-10-15

    We present the results of magnetic properties and entanglement for kagome lattice using Heisenberg model with two- and three-site exchange interactions in strong magnetic field. Kagome lattice correspond to the third layer of fluid {sup 3}He absorbed on the surface of graphite. The magnetic properties and concurrence as a measure of pairwise thermal entanglement are studied by means of variational mean-field like treatment based on Gibbs-Bogoliubov inequality. The system exhibits different magnetic behaviors depending on the values of the exchange parameters (J{sub 2}, J{sub 3}). We have obtained the magnetization plateaus at low temperatures. The central theme of the paper is comparing the entanglement and magnetic behavior for kagome lattice. We have found that in the antiferromagnetic region behavior of the concurrence coincides with the magnetic susceptibility one.