Relevant bibliographies by topics / HEISENBERG MODEL; SPIN

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Academic literature on the topic 'HEISENBERG MODEL; SPIN'

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Published: 4 June 2021
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Journal articles on the topic "HEISENBERG MODEL; SPIN"

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FARACH, H. A., R. J. CRESWICK, and C. P. POOLE. "THE RESTRICTED SPIN MODEL." Modern Physics Letters B 04, no. 16 (September 10, 1990): 1029–41. http://dx.doi.org/10.1142/s0217984990001306.

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We present a novel anisotropic Heisenberg model in which the classical spin is restricted to a region of the unit sphere which depends on the value of the anisotropy parameter Δ. In the limit Δ→1, we recover the Ising model, and in the limit Δ→0, the isotopic Heisenberg model. Monte Carlo calculations are used to compare the critical temperature as a function of the anisotropy parameter for the restricted and unrestricted models, and finite-size scaling analysis leads to the conclusion that for all Δ>0 the model belongs to the Ising universality class. For small A the critical behavior is clearly seen in histograms of the transverse and longitudinal (z) components of the magnetization.
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SZETO, K. Y. "HIGH TEMPERATURE SERIES ANALYSIS OF SUSCEPTIBILITY DATA OF La2CuO4." Modern Physics Letters B 04, no. 04 (February 20, 1990): 283–87. http://dx.doi.org/10.1142/s0217984990000350.

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The zero-field magnetic susceptibility of La 2 CuO 4 is analyzed using high temperature series for five different magnetic Hamiltonians in two-dimensions: spin 1/2 Heisenberg model, spin 1/2 XY model, classical Heisenberg model, classical XY model, and the Ising model. The goodness of fit indicates that the quantum spin 1/2 Heisenberg model is best, with the classical XY model second.
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Afremov, Leonid L., and Aleksandr A. Petrov. "“Average Spin” Approximation in the Heisenberg Model." Applied Mechanics and Materials 752-753 (April 2015): 243–46. http://dx.doi.org/10.4028/www.scientific.net/amm.752-753.243.

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The “average spin” method was developed in terms of Heisenberg model. The average magnetic moment’s depending average of the temperature, the number of the nearest neighbors and spin of the atom has been calculated. It’s shown that the Curie temperature decreases with the spin of the atom.
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ITO, NOBUYASU, and MASUO SUZUKI. "COHERENT-ANOMALY METHOD FOR QUANTUM SPIN SYSTEMS." International Journal of Modern Physics B 02, no. 01 (February 1988): 1–11. http://dx.doi.org/10.1142/s0217979288000020.

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The coherent-anomaly method (CAM) is applied to the Heisenberg model to test the applicability of the CAM for quantum spin systems. The Weiss, Bethe and constant coupling approximations are tried for the Heisenberg model on the simple cubic lattice and estimate the critical exponents of the susceptibility and spontaneous magnetization using the CAM. The results show that the CAM is also powerful for quantum spin systems. The detailed results of the Bethe approximation of the spin-1/2 isotropic Heisenberg model are presented.
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Felcy, A. Ludvin, and M. M. Latha. "A spin rotator model for Heisenberg helimagnet." Physica A: Statistical Mechanics and its Applications 491 (February 2018): 1–12. http://dx.doi.org/10.1016/j.physa.2017.08.059.

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ANGELUCCI, ANTIMO. "ORDER PARAMETERS OF FRUSTRATED SPIN SYSTEMS." International Journal of Modern Physics B 05, no. 04 (February 20, 1991): 659–74. http://dx.doi.org/10.1142/s0217979291000365.

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We present a study of the ground states and of the low energy fluctuations of the frustrated Heisenberg spin chain, both classical and quantum. Analyzing this simple model we draw some general conclusions about the antiferro-helix “transition” of general classical Heisenberg models. We derive the low energy action describing the fluctuations about the helical phases and we infer the possible existence of nontrivial topological terms in the quantum counterparts.
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YANG, J., W. P. SU, and C. S. TING. "MODIFIED SCHWINGER BOSON THEORY OF QUANTUM HEISENBERG MODEL." Modern Physics Letters B 05, no. 24n25 (October 1991): 1695–701. http://dx.doi.org/10.1142/s0217984991002045.

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We proposed a modified Schwinger boson theory for quantum Heisenberg model which naturally satisfies the spin identity [Formula: see text], and in which the redundant degrees of freedom due to an average treatment of the constraints are discarded by introducing new boson operators. The results, either for free energy or for spin-spin correlation are exactly the same as those of Takahashi’s modified spin wave theory.7 This theory provides a unified approach to study the ferromagnet and antiferromagnet on equal footing. As such it would be a good starting point for discussing antiferromagnetism in the presence of holes, where ferromagnetic component plays an important role.
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Ng, K. K. "Bilayered Spin-S Heisenberg Model in Fractional Dimensions." International Journal of Modern Physics B 12, no. 18 (July 20, 1998): 1809–12. http://dx.doi.org/10.1142/s0217979298001034.

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The ground state and the phase transitions of the bilayered spin-S anti-ferromagnetic Heisenberg model were studied by Ng et al.1 by using the Schwinger boson mean field theory. In this paper, an analytic continuation of the self-consistent equations is carried out in order to study the extension of the model to fractional dimensions from 1 to 2. Decreasing the dimensionality from 2 has an effect similar to that of decreasing the spin S. The corresponding phase diagram and phase transition will also be discussed.
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BELINICHER, V. I., and L. V. POPOVICH. "QUARTET STATE OF THE TWO-DIMENSIONAL HEISENBERG MODEL WITH THE SPIN-½ ON A SQUARE LATTICE." International Journal of Modern Physics B 08, no. 16 (July 20, 1994): 2203–19. http://dx.doi.org/10.1142/s0217979294000890.

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The low-energy properties of the two-dimensional Heisenberg model with spin-½ on a square lattice are investigated on the basis of the local dimer order. The lattice is divided into square blocks consisting of the quartets of spins. The spin variables and the Heisenberg Hamiltonian are expressed in terms of the low-energy quartet variables. On the basis of the Dyson-Maleev representation, the spin-wave theory of the quartet state is developed. The spectrum of the lower magnon excitations consists of three degenerate modes with the energy gap Δ=0.17J. The ground state energy per spin E/N=−0.6J. Calculations of the basic corrections make the work complete.
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Prata, G. N., P. H. Penteado, F. C. Souza, and Valter L. Líbero. "Spin-density functional for exchange anisotropic Heisenberg model." Physica B: Condensed Matter 404, no. 19 (October 2009): 3151–54. http://dx.doi.org/10.1016/j.physb.2009.07.066.

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Dissertations / Theses on the topic "HEISENBERG MODEL; SPIN"

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Lozano, Dairon Andrés Jiménez. "Modelo de Heisenberg Antiferromagnético de spin-1/2 na rede triangular com interações competitivas." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-21092016-212043/.

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Nesta dissertação estudamos sistemas de spins em redes de baixa dimensionalidade e em temperatura nula, analisando suas transições de fases quânticas. Mais precisamente, estu- damos as propriedades do estado fundamental e as possíveis transições de fase do modelo de Heisenberg quântico antiferromagnético de spin-1/2, com interações entre os primeiros e segundos vizinhos, em diversas redes, e em particular na rede triangular, que é o foco de nosso estudo. Para a obtenção do estado fundamental aproximado, usamos um método variacional em que a rede é particionada num conjunto de plaquetas de sítios. O estado fundamental é escrito como um produto tensorial dos estados das plaquetas. Para a rede triangular, escolhemos um triângulo como uma plaqueta. Quatro fases foram encontra- das: a fase antiferromagnética de Néel, a colinear, a fase de Néel modificada e aquela que denominamos de ligação covalente ressonante. Obtivemos as energias e as magnetizações de subrede em função da razão entre as interações de primeiros e segundos vizinhos. En- tre as fases de Néel e a colinear, podemos observar a fase de ligação covalente ressonante caracterizada como um singleto quanto ao spin de cada plaqueta.
In this thesis we study spin systems in low-dimensional lattices at zero temperature, analyzing their quantum phase transitions. More precisely, we study the properties of the ground state and the possible phase transitions in the antiferromagnetic spin-1/2 quan- tum Heisenberg model with interaction between the first and second neighbors, in several lattices, and in particular in the triangular lattice, which is the focus of our study. To obtain the approximate ground state, we use a variational method in which the lattice is partitioned into a set of plates of sites. The ground state is written as a tensor product of the states of plates. For the triangular lattice, we choose a triangle as a plate. Four phases were found: the antiferromagnetic Néel phase, the collinear, the modified Néel phase and that we call resonating valence bond. We obtained the energy and the magnetization as a function of the ratio of the interactions between the first and second neighbor sites. Between the Néel and collinear phases, we can observe the spin resonating valence bond phase, characterized as a singlet with respect to the spin of each plate.
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Fong, Manson Cheuk-Man. "Heisenberg model with spin anisotropy on the Kagomé lattice /." View abstract or full-text, 2008. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202008%20ZFONG.

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Rowan, David Glenn. "Theoretical studies of disordered short-range spin models." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299226.

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Szàllàs, Attila. "Heisenberg antiferromagnetic model on 2D quasiperiodic tilings." Paris 11, 2008. http://www.theses.fr/2008PA112174.

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Le pavage de Penrose est une structure quasipériodique bidimensionnelle, utilisée dans la description des composés quasicristallins. Cette structure est parfaitement ordonnée, avec une symétrie de rotation cinq et elle est invariante sous un changement d'échelle par un facteur τ. Nous avons étudié les propriétés d'un modèle d'Heisenberg sur le pavage de Penrose construit à partir de losanges, en utilisant une méthode de développement en ondes de spin. Les énergies et fonctions d'ondes des magnons (quantum d'une onde des spins) ont été étudiées dans le cadre d'une théorie linéarisée. Les propriétés spatiales des modes propres ont été étudiées en détail. A basse énergie, nous trouvons que les états propres sont relativement étendus. Une analyse multifractale montre qu'ils sont de type “critique”, ayant une distribution d'exposants multifractaux. L'énergie de l’état fondamental de cette antiferromagnetique, et la distribution des aimantations locales dans cet état ont été calculés. Des projections dans l’espace perpendiculaire montrent la simplicité sous-jacente de ce état "complexe". Un simple modèle analytique, l’étoile de Heisenberg à deux niveaux, a été présenté pour expliquer de la distribution d'aimantation locales dans ce système antiferromagnétique. Dans une dernière partie, les effets de désordre de type “phason” sont considérés. Nous avons progressivement augmenté le désordre géometrique de la structure originale. Nous montrons, à l'aide d'un développement en ondes des spin ainsi que par QMC, que l'aimantation alternée diminue exponentiellement vers une valeur asymptote en fonction du désordre. La vitesse des ondes des spin augmente avec le désordre
The Penrose tiling is a perfectly ordered two dimensional structure with fivefold symmetry and scale invariance. We considered a Heisenberg antiferromagnet on the Penrose rhombus tiling, and showed it has an inhomogeneous Neel-ordered ground state. Spin wave energies and wavefunctions were studied in the linear spin wave approximation. Spatial properties of eigenmodes were characterized in several different ways. At low energies, eigenstates were found to be relatively extended, and appeared to show multifractal scaling. At higher energies, states were found to be more localized, and, depending on the energy, confined to sites of a specified coordination number. The ground state energy of this antiferromagnet, and local staggered magnetizations were calculated. Perpendicular space projections were shown, showing the underlying simplicity of this “complex" ground state. A simple analytical model, the two-tier Heisenberg star, was presented to explain the staggered magnetization distribution in this antiferromagnetic system. The effects of a novel type of disorder in a two dimensional quantum antiferromagnet is considered. The original bipartite structure is geometrically disordered in such a way that no frustration is introduced, and the system retains a Neel ordered ground state. We show, using a linear spin wave expansion and QMC, that the staggered moment decreases exponentially as a function of increasing disorder. The spatial distribution of staggered magnetizations becomes more homogeneous compared to the deterministic tiling, the effective spin wave velocity increases with disorder, and singularities in the magnon spectrum and wavefunctions are partly smoothed
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Oliveira, Ravenna Rodrigues. "Modelo de Heisenberg para cadeia de spins." reponame:Repositório Institucional da UFC, 2016. http://www.repositorio.ufc.br/handle/riufc/19729.

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OLIVEIRA, R. R. Modelo de Heisenberg para cadeia de spins. 2016. 58 f. Dissertação (Mestrado em Física) – Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2016.
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Everyday new technological inventions arrives in the world, improving the life of the society as one. For new devices to have improvements, science needs to be improved too. Within science, a subject that stands out is the magnetism properties of the materials, like ferromagnetic materials. Due to the studies about the magnetism properties of the materials become possible the criation of computer hard drive. In this dissertation, we use the Heisenberg model to better understand the spin waves, which commonly appear in magnetic materials. This model considers the exchange interation of spins, together with the Zeeman effect. In this dissertation we use the eisenberg model for spin waves applied to some networks. The study for a two layer network where one of them is displaced in relation to the other was done. The behavior for a network displaced to the left and a network equally dislocated to the right is the same. Due to the helical structure of an RNA molecule we study the Heisenberg model in a network around a cylinder. For this network, we found that case where the network is symmetrically displaced is degenerate, which can be broke by changing the network configuration, so there is no symmetry in the system.
Todo dia novas invenções tecnológicas surgem no mundo, melhorando a vida da sociedade como um todo. Para que os novos dispositivos estejam cada vez mais evoluindo, a ciência também precisa estar evoluindo. Dentro da ciência, um assunto que ganha destaque são as propriedades magnéticas dos materiais, tais quais materiais ferromagnéticos. A partir do estudo de materiais magnéticos foi possível a fabricação de dispositivos como o HD de computadores. Nos sistemas ferromagnéticos os spins vizinhos estão acoplados uns aos outros por meio da interação de troca, possuindo modos coletivos chamados de ondas de spin. Para entender as propriedades de ondas de spin utiliza-se o modelo de Heisenberg, que considera o termo de troca, juntamente com o efeito Zeeman. Nesta dissertação utilizamos o modelo de Heisenberg para ondas de spins para algumas redes. O estudo para uma rede de duas camadas onde uma é deslocada em relação à outra foi realizado, observando que o comportamento para uma rede deslocada para a esquerda e uma rede igualmente deslocada para a direita é o mesmo. Motivados pelo formato helicoidal da molécula de RNA, estudamos uma rede ao redor de um cilindro. O caso onde a rede é disposta simetricamente é encontrado degenerescência, que pode ser desfeita alterando a configuração da rede de modo que não haja mais simetria.
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Silva, Wanêssa Façanha da. "Ondas de spin em redes decoradas." reponame:Repositório Institucional da UFC, 2014. http://www.repositorio.ufc.br/handle/riufc/13700.

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SILVA, Wanêssa Façanha. Ondas de spin em redes decoradas. 2014. 62 f. Dissertação (Mestrado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2014.
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Low-dimensional systems have attracted much attention lately due to systems such as graphene and carbon nanotubes. Such systems have great potential for technological applications. In particular the creation of electronic devices due to their specific electronic properties. In this sense , the study of other systems in low dimension becomes urgent. More specifically , the study of magnetic properties of materials at low dimensionality also brings great new features in the behavior of ferromagnetic systems . The behavior of spin waves in such systems may be important to the study of spintronic and the development of new devices and magnetic memories . Thus in this work we aim to study the behavior of ferromagnetic spin waves in two-dimensional systems . For two-dimensional systems we consider here two-dimensional networks decorated . The decorations are introduced to generate networks with more than one basic atom in the unit cell of the system to study the richness of the spectrum of spin waves due to these changes . At first deal with a superimposition of square networks where the displacement of these networks depends on the control parameters alpha and beta . We also use the superposition of a square on a hexagonal network.
Sistema de baixa dimensionalidade têm atraído uma grande atenção ultimamente devido a sistemas como grafeno e nanotubos de carbono. Tais sistemas têm grandes possibilidades de aplicações tecnológicas, em particular na criação de dispositivos eletrônicos, devido às suas propriedades eletrônicas específicas. Nesse sentido, o estudos de outros sistemas em baixa dimensão se torna urgente. Mais especificamente, o estudo de propriedades magnéticas de materiais de materiais em baixa dimensionalidade também trás grandes novidades no comportamento de sistemas ferromagnéticos. O comportamento de ondas de spin em tais sistemas pode ser para o estudo da spintrônica e o desenvolvimento de novos aparelhos e memórias magnéticas. Dessa forma temos como objetivo nesse trabalho estudar o comportamento de ondas de spin em sistemas bidimensionais ferromagnéticos. Por sistemas bidimensionais consideramos aqui redes bidimensionais decoradas. As decorações são introduzidas para gerar redes com mais de um átomo na base da célula unitária da rede para estudarmos a riqueza do espectro das ondas de spin devido a essas modificações. A princípio tratamos com uma superposição de redes quadradas onde o deslocamento dessas redes depende dos parâmetros de controle α e β. Também usamos a superposição de um rede quadrada sobre um hexagonal.
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Souza, Fabiano Caetano de. "Método de diagonalização iterativa para o modelo de Heisenberg." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-13092010-103541/.

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Nesta tese desenvolvemos um método numérico para diagonalizar o Hamiltoniano de Heisenberg iterativamente. O método consiste basicamente em diagonalizar cadeias de spins, cada vez maiores, em que cada passo da diagonalização corresponde à adição de um novo spin à cadeia. A base de vetores para calcular o Hamiltoniano de uma cadeia de N spins, HN, é construída por meio do produto direto dos autovetores do Hamiltoniano Hn-1 da rede diagonalizada no passo anterior, pelos autoestados correspondentes ao N-ésimo spin adicionado. Além de usar a comutação do Hamiltoniano com a componente azimutal do spin total, Sz, prática comum em outros métodos, usufruímos da conservação com o quadrado do spin total, S2. Para uma classe específica de redes também implementamos a simetria de reflexão. Obtemos o espectro completo de energia de cadeias de spins 1/2 com até 20 sítios, para as quais mostramos resultados da dependência com a temperatura da susceptibilidade magnética e do calor específico, para redes com impurezas tipo spin substitucionais, com defeitos nas ligações ou com efeitos de bordas, isto é, para sistemas sem invariância translacional. Usualmente essa restrição impõe enormes dificuldades em métodos tradicionais. Para diagonalizar cadeias com um número maior de sítios, implementamos um procedimento que seleciona os estados de mais baixa energia para serem usados na base de vetores do passo seguinte. Com esse tipo de truncamento de estados, fomos capazes de obter o estado fundamental e alguns estados de baixa energia de cadeias com mais de uma centena de sítios, com precisão de até cinco algarismos significativos. Nossos resultados reproduzem os da literatura para os casos conhecidos, em geral sistemas homogêneos. As aproximações desenvolvidas recentemente no contexto da Teoria do Funcional da Densidade, aplicada ao modelo de Heisenberg, e que também se aplicam a sistemas inomogêneos, estão em conformidade com nossos resultados numericamente exatos. Generalizamos o método para diagonalizar escadas de spins 1/2. Calculamos o estado fundamental e o gap de energia desse sistema, onde variamos a razão entre os acoplamentos ao longo das pernas da escada e ao longo dos degraus da mesma; nossos resultados são comparados com os da literatura. Apresentamos também a implementação do método iterativo no modelo de Hubbard, que descreve um sistema de spins itinerantes. Sabe-se que no regime de alta repulsão Coulombiana entre os spins e densidade um (número de spins igual ao número de sítios da cadeia), esse modelo é mapeado no modelo de Heisenberg, resultado que é verificado numericamente em nosso procedimento por meio do cálculo de energias de ambos os modelos em um regime paramétrico apropriado.
In this Thesis we develop a numerical method to diagonalize the Heisenberg model iteratively. In essence, we diagonalize spin chains in steps, each one corresponding to an addition of a spin to a smaller chain. The basis vectors to calculate the Hamiltonian of a N-spin chain, HN, is built by means of the direct product of the eigenvectors of the (N-1)-spin Hamiltonian, diagonalized on the previous step, by the eigenstates of the N-th added spin. Besides the common use of the conservation of the z-component of the total spin, Sz, we also exploit the conservation of the squared total spin, S2. For a specific class of spin systems we also implemented the reflection symmetry. We obtain the entire energy spectrum of spin-1/2 chains up to 20 sites, for which we show the temperature dependence of the magnetic susceptibility and specific heat, for systems with substitutional impurity spins, bond defects, border effects, i.e., for systems without translational invariance. This normally imposes enormous restrictions in many traditional methods. In order to diagonalize chains with a larger number of sites we implemented a procedure that selects lower energy states to be used in the basis vector on the next step. Using this truncation scheme, we are able to obtain low-lying energy states for chains with more than a hundred sites, up to five significant figures of accuracy. Our results reproduce those of the literature for the known cases, in general homogeneous systems. The approaches recently developed in the context of Density Functional Theory to the Heisenberg model, which also apply to inhomogeneous systems, are consistent with our numerical results. We generalize the method to diagonalize spin-1/2 ladders. We calculate the ground-state and the energy gap of this system, for arbitrary ratio of the couplings along the lags or over the rungs of the ladder. We also present the implementation of our iterative method to the Hubbard model, which describes a system of itinerant spins. It is known that in the regime of high Coulomb repulsion between the spins and unitary density (number of spins equal to the number of sites in the chain), this model is mapped onto Heisenberg one, a result which is verified numerically in our procedure by calculating the energy spectrum of both models in na appropriated parametric regime.
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Silva, WanÃssa FaÃanha da. "Ondas de spin em redes decoradas." Universidade Federal do CearÃ, 2014. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=12439.

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Sistema de baixa dimensionalidade tÃm atraÃdo uma grande atenÃÃo ultimamente devido a sistemas como grafeno e nanotubos de carbono. Tais sistemas tÃm grandes possibilidades de aplicaÃÃes tecnolÃgicas, em particular na criaÃÃo de dispositivos eletrÃnicos, devido Ãs suas propriedades eletrÃnicas especÃficas. Nesse sentido, o estudos de outros sistemas em baixa dimensÃo se torna urgente. Mais especificamente, o estudo de propriedades magnÃticas de materiais de materiais em baixa dimensionalidade tambÃm trÃs grandes novidades no comportamento de sistemas ferromagnÃticos. O comportamento de ondas de spin em tais sistemas pode ser para o estudo da spintrÃnica e o desenvolvimento de novos aparelhos e memÃrias magnÃticas. Dessa forma temos como objetivo nesse trabalho estudar o comportamento de ondas de spin em sistemas bidimensionais ferromagnÃticos. Por sistemas bidimensionais consideramos aqui redes bidimensionais decoradas. As decoraÃÃes sÃo introduzidas para gerar redes com mais de um Ãtomo na base da cÃlula unitÃria da rede para estudarmos a riqueza do espectro das ondas de spin devido a essas modificaÃÃes. A princÃpio tratamos com uma superposiÃÃo de redes quadradas onde o deslocamento dessas redes depende dos parÃmetros de controle α e β. TambÃm usamos a superposiÃÃo de um rede quadrada sobre um hexagonal
Low-dimensional systems have attracted much attention lately due to systems such as graphene and carbon nanotubes. Such systems have great potential for technological applications. In particular the creation of electronic devices due to their specific electronic properties. In this sense , the study of other systems in low dimension becomes urgent. More specifically , the study of magnetic properties of materials at low dimensionality also brings great new features in the behavior of ferromagnetic systems . The behavior of spin waves in such systems may be important to the study of spintronic and the development of new devices and magnetic memories . Thus in this work we aim to study the behavior of ferromagnetic spin waves in two-dimensional systems . For two-dimensional systems we consider here two-dimensional networks decorated . The decorations are introduced to generate networks with more than one basic atom in the unit cell of the system to study the richness of the spectrum of spin waves due to these changes . At first deal with a superimposition of square networks where the displacement of these networks depends on the control parameters alpha and beta . We also use the superposition of a square on a hexagonal network.
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Exler, Matthias. "On classical and quantum mechanical energy spectra of finite Heisenberg spin systems." Doctoral thesis, [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=980110440.

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Szallas, Attila. "Heisenberg antiferromagnetique model sur le pavage quasicrystaux bidimensionnelle." Phd thesis, Université Paris Sud - Paris XI, 2008. http://tel.archives-ouvertes.fr/tel-00358251.

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Le pavage de Penrose est une structure quasipériodique bidimensionnelle, utilisée dans la description des composés quasicristallins. Cette structure est parfaitement ordonnée, avec une symétrie de rotation cinq et elle est invariante sous un changement d'échelle par un facteur $\tau$ (le nombre d'or). On s'attend à ce que les propriétés d'un modèle d'antiferromagnétisme dans un tel système diffèrent nettement de celles des antiferromagnétiques périodiques. Nous avons étudié les propriétés d'un modèle d'Heisenberg sur le pavage de Penrose construit à partir de losanges, en utilisant une méthode de développement en ondes de spin. Les énergies et fonctions d'ondes des magnons (quantum d'une onde des spins) ont été étudiées dans le cadre d'une théorie linéarisée. A basse énergie, on trouve une loi de dispersion linéaire, comme dans d'autres antiferromagnetiques bipartites, avec une vitesse effective de l'onde de spin inférieure à celle d'un réseau carré équivalent. Les propriétés spatiales des modes propres ont été étudiées en détail. A basse énergie, nous trouvons que les états propres sont relativement étendus. Une analyse multifractale montre qu'ils sont de type “critique”, ayant une distribution d'exposants multifractaux. Aux énergies plus élevées, les états deviennent plus localisés, et, en fonction de l'énergie, l'amplitude de la fonction d'onde est non-nulle autour d'un sous-ensemble de sites d'une valeur de coordinence donnée.

L'énergie de l'état fondamental de cette antiferromagnetique, et la distribution des aimantations locales dans cet état ont été calculés. Des projections dans l'espace perpendiculaire montrent la simplicité sous-jacente de ce état "complexe". Un simple modèle analytique, l'étoile de Heisenberg à deux niveaux, a été présenté pour expliquer de la distribution d'aimantation locales dans ce système antiferromagnétique.

Dans une dernière partie, les effets de désordre de type “phason” sont considérés. Nous avons progressivement augmenté le désordre géometrique de la structure originale. Nous avons trouvé que l'etat fondamental conserve son ordre de Néel, mais que la forme de la distribution ainsi que la norme des aimantations sont modifiés. Nous montrons, à l'aide d'un développement en ondes des spin ainsi que par Quantum Monte Carlo, que l'aimantation alternée diminue exponentiellement vers une valeur asymptote en fonction du désordre. La distribution spatiale de magnetizations locales devient plus homogène par rapport à pavage parfait. La vitesse des ondes des spin augmente avec le désordre, et les singularités dans le spectre et les functions d'onde sont en partie lissées. Ces résultats sont comparés avec des résultats connus dans des systèmes désordonnés.
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Books on the topic "HEISENBERG MODEL; SPIN"

1

Sricheewin, Chanun. The coupled-cluster method treatment of spin-1/2 Heisenberg 2-leg ladder model. Manchester: UMIST, 1998.

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Boudreau, Joseph F., and Eric S. Swanson. Quantum spin systems. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198708636.003.0022.

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The quantum mechanical underpinnings of magnetism are explored via the Heisenberg model of antiferromagnetism. The Lanczos algorithm is developed and applied to obtain ground state properties of the anisotropic antiferromagnetic Heisenberg spin chain. In particular, the phase diagram for the system magnetization is determined. A quantum Monte Carlo method that is appropriate for discrete systems is also presented. The method leverages the similarity between the Schrödinger equation and the diffusion equation to compute energy levels. The formalism necessary to compute ground state matrix elements is also developed. Finally, the method is tested with an application to the spin chain.
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Eriksson, Olle, Anders Bergman, Lars Bergqvist, and Johan Hellsvik. The Atomistic Spin Dynamics Equation of Motion. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780198788669.003.0004.

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From the information obtained in DFT, in particular the magnetic moments and the Heisenberg exchange parameters, one has the possibility to make a connection to atomistic spin-dynamics. In this chapter the essential features of this connection is described. It is also discussed under what length and time-scales that this approach is a relevant approximation. The master equation of atomistic spin-dynamics is derived, and discussed in detail. In addition we give examples of how this equation describes the magnetization dynamics of a few model systems.
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W, Lovesey S., Rutherford Appleton Laboratory, and Council For The Central Laboratory of The Research Councils., eds. A theory of spin correlations and neutron scattering from paramagnetic materials based on the Ising-Heisenberg model in one, two and three space dimensions. Chilton: Rutherford Appleton Laboratory, 1996.

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Eckle, Hans-Peter. Models of Quantum Matter. Oxford University Press, 2019. http://dx.doi.org/10.1093/oso/9780199678839.001.0001.

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This book focuses on the theory of quantum matter, strongly interacting systems of quantum many–particle physics, particularly on their study using exactly solvable and quantum integrable models with Bethe ansatz methods. Part 1 explores the fundamental methods of statistical physics and quantum many–particle physics required for an understanding of quantum matter. It also presents a selection of the most important model systems to describe quantum matter ranging from the Hubbard model of condensed matter physics to the Rabi model of quantum optics. The remaining five parts of the book examines appropriate special cases of these models with respect to their exact solutions using Bethe ansatz methods for the ground state, finite–size, and finite temperature properties. They also demonstrate the quantum integrability of an exemplary model, the Heisenberg quantum spin chain, within the framework of the quantum inverse scattering method and through the algebraic Bethe ansatz. Further models, whose Bethe ansatz solutions are derived and examined, include the Bose and Fermi gases in one dimension, the one–dimensional Hubbard model, the Kondo model, and the quantum Tavis–Cummings model, the latter a model descendent from the Rabi model.
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Book chapters on the topic "HEISENBERG MODEL; SPIN"

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Wysin, G. M., M. E. Gouvea, A. R. Bishop, and F. G. Mertens. "Classical Spin Dynamics in the Two-Dimensional Anisotropic Heisenberg Model." In Springer Proceedings in Physics, 40–48. Berlin, Heidelberg: Springer Berlin Heidelberg, 1988. http://dx.doi.org/10.1007/978-3-642-93400-1_5.

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Muminov, Kh Kh, and Valirii K. Fedyanin. "Nonlinear Spin Waves and Magnet-Acoustic Resonance in the Model of Heisenberg Magnet." In Mathematical Models of Non-Linear Excitations, Transfer, Dynamics, and Control in Condensed Systems and Other Media, 205–20. Boston, MA: Springer US, 1999. http://dx.doi.org/10.1007/978-1-4615-4799-0_18.

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Sisson, C. J., and R. J. Creswick. "Decoupled-Cell Monte-Carlo Calculations of Critical Properties of the Spin-1/2 Heisenberg Model." In Springer Proceedings in Physics, 204–8. Berlin, Heidelberg: Springer Berlin Heidelberg, 1993. http://dx.doi.org/10.1007/978-3-642-78448-4_26.

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Gutkin, Eugene. "Heisenberg—Ising Spin Chain: Plancherel Decomposition and Chebyshev Polynomials." In Calogero—Moser— Sutherland Models, 177–92. New York, NY: Springer New York, 2000. http://dx.doi.org/10.1007/978-1-4612-1206-5_12.

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Porsezian, K. "On the Discrete and Continuum Integrable Heisenberg Spin Chain Models." In NATO ASI Series, 243–48. Boston, MA: Springer US, 1993. http://dx.doi.org/10.1007/978-1-4899-1609-9_42.

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Matsubara, F., T. Iyota, and S. Inawashiro. "A Hybrid Monte-Carlo Spin-Dynamics Method and Its Applications to the ±J Heisenberg Models in Three Dimensions." In Springer Proceedings in Physics, 219–24. Berlin, Heidelberg: Springer Berlin Heidelberg, 1992. http://dx.doi.org/10.1007/978-3-642-84821-6_40.

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Pires, Antonio Sergio Teixeira. "The Heisenberg model." In Theoretical Tools for Spin Models in Magnetic Systems. IOP Publishing, 2021. http://dx.doi.org/10.1088/978-0-7503-3879-0ch1.

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8

Eckle, Hans-Peter. "The Anisotropic Heisenberg Quantum Spin Chain." In Models of Quantum Matter, 491–501. Oxford University Press, 2019. http://dx.doi.org/10.1093/oso/9780199678839.003.0013.

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This chapter introduces the Heisenberg model, a fully quantum mechanical model that describes the magnetism of localized magnetic moments. The one-dimensional version of the Heisenberg model, the Heisenberg quantum spin chain, provides a good picture of magnetic materials that belong to a class of insulating magnetic materials where the interaction of the magnetic moments in one particular direction is much larger than in the perpendicular directions, and which can be described with high accuracy as quasi- one-dimensional magnets. A detailed description of the Heisenberg quantum spin chain is followed by a discussion of its various special cases, in particular the special case of the anisotropic Heisenberg quantum spin chain, the so-called XXZ quantum spin chain. It considers the solution of eigenvalue problem of this quantum spin and leads to Bethe’s conjecture for the wave function.
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Eckle, Hans-Peter. "Thermodynamics of the Isotropic Heisenberg Quantum Spin Chain." In Models of Quantum Matter, 641–54. Oxford University Press, 2019. http://dx.doi.org/10.1093/oso/9780199678839.003.0018.

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This chapter presents the extension of the Bethe ansatz to finite temperature, the thermodynamic Bethe ansatz, for the antiferromagnetic isotropic Heisenberg quantum spin chain, the XXX quantum spin chain. It discusses how the added complications of this model arise from the more complicated structure of excitations of the quantum spin chain, the complex string excitations, which have to be included in the Bethe ansatz thermodynamics. It derives the integral equations of the thermodynamic Bethe ansatz for the XXX quantum spin chain and mentions explicit formulas for the free energy of the quantum spin chain and some interesting physical quantities, especially making contact with predictions of conformal symmetry.
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Eckle, Hans-Peter. "Six-Vertex Model." In Models of Quantum Matter, 454–73. Oxford University Press, 2019. http://dx.doi.org/10.1093/oso/9780199678839.003.0011.

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This chapter considers the special case of the six-vertex model on a square lattice using a trigonometric parameterization of the vertex weights. It demonstrates how, by exploiting the Yang-Baxter relations, the six-vertex model is diagonalized and the Bethe ansatz equations are derived. The Hamiltonian of the Heisenberg quantum spin chain is obtained from the transfer matrix for a special value of the spectral parameter together with an infinite set of further conserved quantum operators. By the diagonalization of the transfer matrix the exact solution of the one-dimensional quantum spin chain Hamiltonian has automatically also been obtained, which is given by the same Bethe ansatz equations.
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Conference papers on the topic "HEISENBERG MODEL; SPIN"

1

Misumi, K., K. Seki, and Y. Ohta. "Spin Excitations in the Square-Lattice Heisenberg Model with Ring-Exchange Interactions." In Proceedings of the International Conference on Strongly Correlated Electron Systems (SCES2013). Journal of the Physical Society of Japan, 2014. http://dx.doi.org/10.7566/jpscp.3.014021.

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Tanamoto, T., K. Ono, Y. X. Liu, and F. Nori. "Dynamic creation of a topologically-ordered Hamiltonian using spin-pulse control in the Heisenberg model." In 2015 International Conference on Solid State Devices and Materials. The Japan Society of Applied Physics, 2015. http://dx.doi.org/10.7567/ssdm.2015.h-7-2.

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Si LAKHAL, B., and A. ABADA. "FOUR-SPINON CONTRIBUTION TO THE DYNAMIC STRUCTURE FACTOR IN THE ANTIFERROMAGNETIC HEISENBERG MODEL." In Proceedings of the 16th International Spin Physics Symposium and Workshop on Polarized Electron Sources and Polarimeters. WORLD SCIENTIFIC, 2005. http://dx.doi.org/10.1142/9789812701909_0099.

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Strečka, Jozef, Lucia Čanová, Kazuhiko Minami, Yurij Holovatch, Bertrand Berche, Nikolai Bogolyubov, and Reinhard Folk. "Weak-universal critical behavior and quantum critical point of the exactly soluble spin-1∕2 Ising-Heisenberg model with the pair XYZ Heisenberg and quartic Ising interactions." In STATISTICAL PHYSICS: MODERN TRENDS AND APPLICATIONS: The 3rd Conference on Statistical Physics Dedicated to the 100th Anniversary of Mykola Bogolyubov. AIP, 2009. http://dx.doi.org/10.1063/1.3284411.

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BISHOP, R. F., P. H. Y. LI, R. DARRADI, and J. RICHTER. "THE SPIN-1/2 AND SPIN-1 QUANTUM J1−J′1−J2 HEISENBERG MODELS ON THE SQUARE LATTICE." In Proceedings of the 14th International Conference. WORLD SCIENTIFIC, 2008. http://dx.doi.org/10.1142/9789812779885_0034.

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