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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zinenko V. I.
Заглавие : The cluster investigation of the q-state potts-model
Место публикации : Phys. Status Solidi B. - 1982. - Vol. 114, Is. 2. - P.695-703. - ISSN 0370-1972, DOI 10.1002/pssb.2221140248
Примечания : Cited References: 26
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : KHRUSTALEV B. P., BALAEV A. D., POZDNYAKOV V. G., Vershinina L. I.
Заглавие : EXCHANGE INTERACTION IN FERROMAGNETIC FE-SIO FILMS WITH CLUSTER STRUCTURE
Место публикации : Fiz. Tverd. Tela: MEZHDUNARODNAYA KNIGA, 1985. - Vol. 27, Is. 11. - P3222-3229. - ISSN 0367-3294
Примечания : Cited References: 29
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : VAKS V. G., ZINENKO V. I.
Заглавие : THERMODYNAMICS OF 6-VERTEX MODELS IN DIRECT AND STAGGERED ELECTRIC-FIELDS IN THE CLUSTER APPROXIMATION
Разночтения заглавия :авие SCOPUS: Thermodynamics of six-vertex models in direct and staggered electric fields in the cluster approximation
Место публикации : JOURNAL OF PHYSICS C-SOLID STATE PHYSICS: IOP PUBLISHING LTD, 1986. - Vol. 19, Is. 17. - P3083-3104. - ISSN 0022-3719, DOI 10.1088/0022-3719/19/17/007
Примечания : Cited References: 21
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Markel V. A., Shalaev V. M., Poliakov E. Y., George T. F.
Заглавие : Numerical studies of second- and fourth-order correlation functions in cluster-cluster aggregates in application to optical scattering
Место публикации : Phys. Rev. E: AMERICAN PHYSICAL SOC, 1997. - Vol. 55, Is. 6. - P7313-7333. - ISSN 1063-651X, DOI 10.1103/PhysRevE.55.7313
Примечания : Cited References: 21
Предметные рубрики: DIFFUSION-LIMITED AGGREGATION
COLLOIDAL AGGREGATION
FRACTAL CLUSTERS
ANTICORRELATION
SIMULATIONS
Аннотация: Two- and four-point density correlation functions p(2)(r) and p(4)(r) are studied numerically and theoretically in computer-generated three-dimensional lattice cluster-cluster aggregates (CCA) with the number of particles N up to 20 000 in application to the light scattering problem. The ''pure'' aggregation algorithm is used, where subclusters of all possible sizes are allowed to collide. We find that large CCA clusters demonstrate pronounced multiscaling. In particular, the fractal dimension determined from the slope of p(2)(r) at small distances differs from that found from the dependence of the radius of gyration on the number of monomers (according to our data, 1.80 and 1.94, respectively). We also consider different functional forms for p(2) and their general properties and applicability. We find that the best fit to the numerical data is provided by the generalized exponential cutoff function with coefficients depending on N. The latter dependence is a manifestation of multiscaling. We propose some theoretical approaches for calculating p(4)(r), assuming p(2)(r) is known. In particular, we find the small-r asymptote for the p(4)(r) and verify it numerically. In addition, we find that p(4)(r) cannot be represented by a scaling dependence with a cutoff function, like p(2)(r) Instead, p(4)(r) is given by an expansion in terms of integer powers of r(2D-3), where D is the fractal dimension (approximate to 1.8 for CCA clusters).
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zharkov S. M., Zhigalov V. S., Kveglis L. I., Lisitsa Y. V., Renskaya K. V., Frolov G. I.
Заглавие : Cluster structure and superlattices in Co and Fe films
Место публикации : JETP Letters. - 1997. - Vol. 65, Is. 12. - P.915-918. - ISSN 0021-3640, DOI 10.1134/1.567449
Примечания : Cited References: 9
Аннотация: The process of dendritic crystallization of Co and Fe films is investigated. Electron-diffraction methods show that fractal growth of dendrites in Co and Fe films proceeds by multiple twinning of the elements of a nanostructure consisting of different clusters with close-packing. The formation of superstructures is explained by a shell model of a cluster structure forming nanocrystallites. (C) 1997 American Institute of Physics.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Nasluzov V. A., Rivanenkov V. V., Gordienko A. B., Neyman K. M., Birkenheuer U., Rosch N.
Заглавие : Cluster embedding in an elastic polarizable environment: Density functional study of Pd atoms adsorbed at oxygen vacancies of MgO(001)
Место публикации : J. Chem. Phys.: AMER INST PHYSICS, 2001. - Vol. 115, Is. 17. - P8157-8171. - ISSN 0021-9606, DOI 10.1063/1.1407001
Примечания : Cited References: 88
Предметные рубрики: TRANSITION-METAL ATOMS
AB-INITIO
OXIDE SURFACES
ELECTRONIC-PROPERTIES
ENERGY CALCULATIONS
MOLECULAR-DYNAMICS
MOTT-LITTLETON
MADELUNG FIELD
IONIC-CRYSTAL
MGO
Ключевые слова (''Своб.индексиров.''): atoms--binding energy--computer simulation--electron energy levels--electronic structure--magnesia--oxygen--palladium--polarization--probability density function--quantum theory--relaxation processes--charged defects--cluster embedding--elastic polarizable environment--electron affinity--oxygen vacancies--adsorption
Аннотация: Adsorption complexes of palladium atoms on F-s, F-s(+), F-s(2+), and O2- centers of MgO(001) surface have been investigated with a gradient-corrected (Becke-Perdew) density functional method applied to embedded cluster models. This study presents the first application of a self-consistent hybrid quantum mechanical/molecular mechanical embedding approach where the defect-induced distortions are treated variationally and the environment is allowed to react on perturbations of a reference configuration describing the regular surface. The cluster models are embedded in an elastic polarizable environment which is described at the atomistic level using a shell model treatment of ionic polarizabilities. The frontier region that separates the quantum mechanical cluster and the classical environment is represented by pseudopotential centers without basis functions. Accounting in this way for the relaxation of the electronic structure of the adsorption complex results in energy corrections of 1.9 and 5.3 eV for electron affinities of the charged defects F-s(+) and F-s(2+), respectively, as compared to models with a bulk-terminated geometry. The relaxation increases the stability of the adsorption complex Pd/F-s by 0.4 eV and decreases the stability of the complex Pd/F-s(2+) by 1.0 eV, but it only weakly affects the binding energy of Pd/F-s(+). The calculations provide no indication that the metal species is oxidized, not even for the most electron deficient complex Pd/F-s(2+). The binding energy of the complex Pd/O2- is calculated at -1.4 eV, that of the complex Pd/F-s(2+) at -1.3 eV. The complexes Pd/F-s and Pd/F-s(+) exhibit notably higher binding energies, -2.5 and -4.0 eV, respectively; in these complexes, a covalent polar adsorption bond is formed, accompanied by donation of electronic density to the Pd 5s orbital. (C) 2001 American Institute of Physics.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gorban A., Popova T., Zinovyev A.
Заглавие : Codon usage trajectories and 7-cluster structure of 143 complete bacterial genornic sequences
Разночтения заглавия :авие SCOPUS: Codon usage trajectories and 7-cluster structure of 143 complete bacterial genomic sequences
Место публикации : Physica A: ELSEVIER SCIENCE BV, 2005. - Vol. 353. - P365-387. - ISSN 0378-4371, DOI 10.1016/j.physa.2005.01.043
Примечания : Cited References: 46
Предметные рубрики: DNA-BASE COMPOSITION
ASYMMETRIC SUBSTITUTION PATTERNS
PROTEIN-CODING REGIONS
MICROBIAL GENOMES
GENE IDENTIFICATION
MARKOV-MODELS
G+C CONTENT
BIAS
PREDICTION
SELECTION
Ключевые слова (''Своб.индексиров.''): genome--cluster--codon usage--correlations--entropy--mean field--cluster--codon usage--correlations--entropy--genome--mean field--approximation theory--correlation methods--database systems--entropy--functions--genes--mathematical models--clusters--codon usage--genomes--mean field--bacteria
Аннотация: Three results are presented. First, we prove the existence of a universal 7-cluster structure in all 143 completely sequenced bacterial genomes available in Genbank in August 2004, and explained its properties. The 7-cluster structure is responsible for the main part of sequence heterogeneity in bacterial genomes. In this sense, our 7 clusters is the basic model of bacterial genome sequence. We demonstrated that there are four basic "pure" types of this model, observed in nature: "parallel triangles", "perpendicular triangles", degenerated case and the flower-like type. Second, we answered the question: how big are the position-specific information and the contribution connected with correlations between nucleotide. The accuracy of the mean-field (context-free) approximation is estimated for bacterial genomes. We show that codon us-age of bacterial genomes is a multi-linear function of their genomic G+C-content with high accuracy (more precisely, by two similar functions, one for eubacterial genomes and the other one for archaea). Description of these two codon-usage trajectories is the third result. All 143 cluster animated 3D-scatters are collected in a database and is made available on our web-site: http://www.ihes.fr/similar to zinovyev/7clusters. (c) 2005 Elsevier B.V. All rights reserved.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Shaykhutdinov K. A., Balaev D. A., Gokhfeld D. M., Kuzmin Y. I., Popkov S. I., Petrov M. I.
Заглавие : Study of current-voltage characteristics of Bi-based high-temperature superconductors with fractal cluster structure
Коллективы : International Workshop on Weak Superconductivity
Место публикации : Physica C. - 2006. - Vol. 435, Is. 1-2. - P.19-22. - ISSN 0921-4534, DOI 10.1016/j.physc.2006.01.010
Примечания : Cited References: 18
Предметные рубрики: NORMAL-PHASE
VORTEX MOTION
TRANSPORT
Ключевые слова (''Своб.индексиров.''): superconducting foam--pinning--critical current density--fractal--percolation--cluster--cluster--critical current density--fractal--percolation--pinning--superconducting foam--bismuth--critical current density (superconductivity)--electric currents--electric potential--foams--percolation (solid state)--polycrystalline materials--cluster--fractal--pinning--superconducting foam--superconducting materials
Аннотация: We study the effect of the structure on critical currents and current-voltage characteristics (CVC's) of foamed bismuth-based polycrystalline high-temperature superconductors (HTSC). The fractal cluster structure of superconducting foams has been observed and the fractal dimension of boundaries between superconducting and normal clusters has been determined. Based on the magnetic and transport properties of the foamed polycrystalline superconductors, we have shown that the initial parts of CVC's of the superconducting foams are described well by the model that accounts the magnetic flux trapping in fractal clusters of a normal phase. (c) 2006 Elsevier B.V. All rights reserved.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Di Valentin C., Neyman K. M., Risse T., Sterrer M., Fischbach E., Freund H. J., Nasluzov V. A., Pacchioni G., Rosch N.
Заглавие : Density-functional model cluster studies of EPR g tensors of F-s(+) centers on the surface of MgO
Разночтения заглавия :авие SCOPUS: Density-functional model cluster studies of EPR g tensors of F s + centers on the surface of MgO
Место публикации : J. Chem. Phys.: AMER INST PHYSICS, 2006. - Vol. 124, Is. 4. - Ст.44708. - ISSN 0021-9606, DOI 10.1063/1.2161190
Примечания : Cited References: 37
Предметные рубрики: ELECTRONIC G-TENSORS
CORRELATION-ENERGY
MGO(001) SURFACE
OXYGEN VACANCIES
SPIN-ORBIT
G-VALUES
ATOMS
APPROXIMATION
COMPLEXES
MOLECULES
Ключевые слова (''Своб.индексиров.''): density-functional model cluster--single-crystalline thin films--spin-orbit interaction--anisotropy--paramagnetic resonance--single crystals--tensors--thin films--magnesium compounds
Аннотация: We report g tensors of surface color centers, so-called F-s(+) centers, of MgO calculated with two density-functional approaches using accurately embedded cluster models. In line with recent UHV measurements on single-crystalline MgO film, we determined only small g-tensor anisotropies and negative shifts Delta g equivalent to g-g(e) for all F-s(+) sites considered, namely, (001)-terrace, step, edge, and corner sites. The g values are very sensitive to the local structure of the defect: relaxation reverses the sign of Delta g. However, accounting for the spin-orbit interaction either self-consistently or perturbatively yields very similar results. In addition to the values of the tensor components, their direction with respect to the surface was determined. In contrast to edges, significant deviations from ideal C-2v symmetry were found for F-s(+) centers at steps. Recent data on single-crystalline thin films are reevaluated in the light of these results. (c) 2006 American Institute of Physics.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Balaev D. A., Belozerova I. L., Gokhfeld D. M., Kashkina L. V., Kuzmin Y. I., Michel C. R., Petrov M. I., Popkov S. I., Shaikhutdinov K. A.
Заглавие : Current-voltage characteristics of a foamed Bi1.8Pb0.3Sr2Ca2Cu3Ox high-temperature superconductor with fractal cluster structure
Разночтения заглавия :авие SCOPUS: Current-voltage characteristics of a foamed Bi1.8Pb 0.3Sr2Ca2Cu3Ox high-temperature superconductor with fractal cluster structure
Место публикации : Phys. Solid State: SPRINGER, 2006. - Vol. 48, Is. 2. - P207-212. - ISSN 1063-7834, DOI 10.1134/S1063783406020016
Примечания : Cited References: 27
Предметные рубрики: T-C SUPERCONDUCTORS
NORMAL-PHASE
VORTEX MOTION
TRANSITION
TRANSPORT
VORTICES
Аннотация: The influence of the structure of foamed polycrystalline bismuth-based superconductors on their critical currents and current-voltage characteristics is studied. It is found that superconducting foams have a fractal structure, and the fractal dimension of the boundary between the normal and superconducting phases is estimated. The magnetic and transport properties of superconducting foams are investigated, and the current-voltage characteristics are obtained in a wide range of currents. The effect of percolation phenomena on vortex pinning in a foamed superconductor is considered. The current-voltage characteristics of the superconducting foams at the beginning of the resistive transition are found to be in good agreement with a model in which a magnetic flux is assumed to be trapped in the fractal clusters of a normal phase.
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11.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Erkaev N. V., Semenov V. S., Biernat H. K.
Заглавие : Magnetic double-gradient instability and flapping waves in a current sheet
Место публикации : Phys. Rev. Lett.: AMER PHYSICAL SOC, 2007. - Vol. 99, Is. 23. - Ст.235003. - ISSN 0031-9007, DOI 10.1103/PhysRevLett.99.235003
Примечания : Cited References: 10
Предметные рубрики: MAGNETOTAIL CURRENT SHEET
CLUSTER
Ключевые слова (''Своб.индексиров.''): magnetic fields--magnetic properties--magnetohydrodynamics--velocity measurement--current sheets--flapping waves--magnetic gradients--stable regions--electromagnetic waves
Аннотация: A new kind of magnetohydrodynamic instability and waves are analyzed for a current sheet in the presence of a small normal magnetic field component varying along the sheet. These waves and instability are related to the existence of two gradients of the tangential (B(tau)) and normal (B(n)) magnetic field components along the normal (del(n)B(tau)) and tangential (del(tau)B(n)) directions with respect to the current sheet. The current sheet can be stable or unstable if the multiplication of two magnetic gradients is positive or negative. In the stable region, the kinklike wave mode is interpreted as so-called flapping waves observed in Earth's magnetotail current sheet. The kink wave group velocity estimated for the Earth's current sheet is of the order of a few tens of kilometers per second. This is in good agreement with the observations of the flapping motions of the magnetotail current sheet.
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12.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aplesnin S. S., Petrakovskii G. A., Miroshnichenko N. I.
Заглавие : Simulation of magnetic properties of the two-dimensional magnetic with anisotropic antiferromagnetic interactions and cluster ordering by quantum Monte Carlo
Место публикации : Phys. Lett. A: ELSEVIER SCIENCE BV, 2008. - Vol. 372, Is. 26. - P4722-4725. - ISSN 0375-9601, DOI 10.1016/j.physleta.2008.05.010
Примечания : Cited References: 12
Предметные рубрики: SPIN SYSTEM
EXCITATIONS
CU3B2O6
MODEL
Ключевые слова (''Своб.индексиров.''): anisotropic antiferromagnetic--cluster ordering--plateau of magnetization--modulated structure--exchange in cu3b2o6--anisotropic antiferromagnetic--cluster ordering--exchange in cu3b2o6--modulated structure--plateau of magnetization
Аннотация: Magnetic with anisotropic anti ferromagnetic exchange interactions and special topology of coupling in the square lattice with spins pairs ordering is studied by quantum Monte Carlo method. The antiferromagnetic order is found to be more stable as compared to spin liquid state. Exchange interactions and wave vector of structure modulation for Cu3B2O6 is estimated. Neel temperature versus strength of exchange in spin pair is calculated. Plateau and modulation of magnetic structure in field magnetization dependence is revealed. (C) 2008 Elsevier B.V. All rights reserved.
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13.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Nikolaev S. V., Ovchinnikov S. G.
Заглавие : Cluster perturbation theory in Hubbard model exactly taking into account the short-range magnetic order in 2 x 2 cluster
Коллективы :
Разночтения заглавия :авие SCOPUS: Cluster perturbation theory in Hubbard model exactly taking into account the short-range magnetic order in 2 × 2 cluster
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2010. - Vol. 111, Is. 4. - P635-644. - ISSN 1063-7761, DOI 10.1134/S1063776110100146
Примечания : Cited References: 23. - The authors thank V. V. Val'kov for fruitful discussions of this work. This research was supported financially by the Russian Foundation for Basic Research (project nos. 09-02-90723-mob_st and 09-02-00127) and by program no. 5.7 of the Presidium of the Russian Academy of Sciences and integration project no. 40 of the Siberian Branch and Ural Division of the Russian Academy of Sciences.
Предметные рубрики: INFINITE DIMENSIONS
SYSTEMS
STATE
Ключевые слова (''Своб.индексиров.''): antiferromagnetic orders--characteristic energy--cluster perturbation theories--coulomb repulsions--density of state--dynamic mean field theories--eigenvalue problem--exact diagonalization--excited levels--finite temperatures--half-filling--hubbard--metal insulator transition temperature--nearest neighbors--numerical solution--pseudo-gap--quasiparticle spectrum--shadow zone--short-range magnetic orders--temperature evolution--zero temperatures--antiferromagnetism--eigenvalues and eigenfunctions--fermi level--hubbard model--mean field theory--metal insulator boundaries--perturbation techniques--semiconductor insulator boundaries--statistical mechanics--metal insulator transition
Аннотация: The cluster perturbation theory is presented in the 2D Hubbard model constructed using X operators in the Hubbard-I approximation. The short-range magnetic order is taken into account by dividing the entire lattice into individual 2 x 2 clusters and solving the eigenvalue problem in an individual cluster using exact diagonalization taking into account all excited levels. The case of half-filling taking into account jumps between nearest neighbors is considered. As a result of numerical solution, a shadow zone is discovered in the quasiparticle spectrum. It is also found that a gap in the density of states in the quasiparticle spectrum at zero temperature exists for indefinitely small values of Coulomb repulsion parameter U and increases with this parameter. It is found that the presence of this gap in the spectrum is due to the formation of a short-range antiferromagnetic order. An analysis of the temperature evolution of the density of states shows that the metal-insulator transition occurs continuously. The existence of two characteristic energy scales at finite temperatures is demonstrated, the larger scale is associated with the formation of a pseudogap in the vicinity of the Fermi level, and the smaller scale is associated with the metal-insulator transition temperature. A peak in the density of states at the Fermi level, which is predicted in the dynamic mean field theory in the vicinity of the metal-insulator transition, is not observed.
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14.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Erkaev N. V., Semenov V. S., Biernat H. K.
Заглавие : Hall magnetohydrodynamic effects for current sheet flapping oscillations related to the magnetic double gradient mechanism
Коллективы :
Место публикации : Phys. Plasmas: AMER INST PHYSICS, 2010. - Vol. 17, Is. 6. - Ст.60703. - ISSN 1070-664X, DOI 10.1063/1.3439687
Примечания : Cited References: 15. - This work is supported by RFBR (Grant Nos. N 07-05-00776-a and N 09-05-91000-ANF_a), and by Program No. 16 of RAS. Additional support is due to the Austrian "Fonds zur Forderung der wissenschaftlichen Forschung" under Project No. I 193-N16 and the "Verwaltungsstelle fur Auslandsbeziehungen" of the Austrian Academy of Sciences.
Предметные рубрики: CLUSTER OBSERVATIONS
MAGNETOTAIL
Аннотация: Hall magnetohydrodynamic model is investigated for current sheet flapping oscillations, which implies a gradient of the normal magnetic field component. For the initial undisturbed current sheet structure, the normal magnetic field component is assumed to have a weak linear variation. The profile of the electric current velocity is described by hyperbolic functions with a maximum at the center of the current sheet. In the framework of this model, eigenfrequencies are calculated as functions of the wave number for the "kink" and "sausage" flapping wave modes. Because of the Hall effects, the flapping eigenfrequency is larger for the waves propagating along the electric current, and it is smaller for the opposite wave propagation with respect to the current. The asymmetry of the flapping wave propagation, caused by Hall effects, is pronounced stronger for thinner current sheets. This is due to the Doppler effect related to the electric current velocity. (C) 2010 American Institute of Physics. [doi:10.1063/1.3439687]
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15.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Yurkin G. Yu., Patrin G. S., Velikanov D. A., Beletsky V. V.
Заглавие : Transport properties of FeSi with cobalt impurities
Место публикации : TRENDS IN MAGNETISM. - 2011. - Vol. 168-169. - С. 493-496. - ISSN 10120394 (ISSN); 9783037850213 (ISBN), DOI 10.4028/www.scientific.net/SSP.168-169.493
Ключевые слова (''Своб.индексиров.''): iron monosilicide--kondo effect--magnetization--resistivity--spindependent scattering--superparamagnetic cluster--cobalt--crystals--electric resistance--electron energy loss spectroscopy--kondo effect--magnetic field effects--magnetic properties--magnetization--magnetoresistance--scattering--superparamagnetism--transport properties--cobalt--electric conductivity--electron scattering--impurities--kondo effect--magnetism--magnetization--experimental investigations--kondo models--magnetoresistance properties--resistivity--si crystals--spin dependent scattering--superparamagnetic clusters--crystal impurities--crystal impurities
Аннотация: The results of experimental investigations of Fe1-xCo xSi crystals in the impurity limit are presented in this article. We made an attempt to study changes of magnetic properties and conductivity in mixed Fe1-xCoxSi crystals in the impurity limit. Magnetoresistance properties are well described in the framework of Kondo model. The presence of Co-subsystem leads to the occurrence of spin-dependent channel in electron scattering conduction.
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16.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zobov V. E., Lundin A. A.
Заглавие : Decay of Multispin Multiple-Quantum Coherent States in the NMR of a Solid and the Stabilization of Their Intensity Profile with Time
Разночтения заглавия :авие SCOPUS: Decay of multispin multiple-quantum coherent states in the NMR of a solid and the stabilization of their intensity profile with time
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2011. - Vol. 113, Is. 6. - P1006-1014. - ISSN 1063-7761, DOI 10.1134/S1063776111140111
Примечания : Cited References: 27
Ключевые слова (''Своб.индексиров.''): cluster sizes--coherent state--decay rate--effective size--experimental data--intensity profiles--coherent light--decay (organic)--stabilization
Аннотация: Variations, experimentally observed in [14], in the intensity profiles of multiple-quantum (MQ) coherences in the presence of two special types of perturbations are explained on the basis of the theory, earlier developed by the authors, of the growth of the effective size of correlated clusters (the number of correlated spins) and the relaxation of MQ coherent states [23]. The intensity and the character of perturbation were controlled by the experimenters. It is shown that the observed stabilization of profiles with time is not associated with the stabilization of the cluster size. Quite the contrary, a cluster of correlated spins monotonically grows, while the observed variations in the intensity profile and its stabilization with time are attributed to the dependence of the decay rate of an MQ coherence on its order (its position in the MQ spectrum). The results of the theory are in good agreement with the experimental data.
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17.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Nikolaev S. V.
Заглавие : Calculation of the Fermi Surface with Complex Topology from Norm-Conserving Cluster Perturbation Theory for Doping Dependent Electronic Structure of the Hubbard Model
Место публикации : JETP Letters. - 2011. - Vol. 93, Is. 9. - P.517-520. - ISSN 0021-3640, DOI 10.1134/S0021364011090116
Примечания : Cited References: 27. - This work was supported by the Presidium of the Russian Academy of Sciences (program no. 18.7); the Russian Foundation for Basic Research (project nos. 09-02-00127, 10-02-90725-mob_st); Siberian Branch, Russian Academy of Sciences (Integration Project no. N40); and the Ministry of Education and Sciences of the Russian Federation (state contract no. P891, Program "Kadry").
Предметные рубрики: QUANTUM OSCILLATIONS
SUPERCONDUCTORS
EVOLUTION
Аннотация: The results of recently developed norm-conserving cluster perturbation theory for doping dependent electronic structure of the Hubbard model are reported. We have found that the momentum distribution of the spectral weight strongly depends on the broadening value delta. At delta = 0.1t, we reproduce the angle-resolved photoemission spectroscopy data, while at delta = 0.01t we obtain two quantum phase transitions. DOI: 10.1134/S0021364011090116
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18.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Bykov A. A., Terent'yev K. Yu., Gokhfeld D. M., Petrov M. I.
Заглавие : Fractal dimension of cluster boundaries in porous polycrystalline HTSC materials
Место публикации : Phys. Solid State: MAIK Nauka-Interperiodica / Springer, 2012. - Vol. 54, Is. 10. - P.1947-1950. - ISSN 1063-7834, DOI 10.1134/S1063783412100095
Примечания : Cited References: 20
Предметные рубрики: CURRENT-VOLTAGE CHARACTERISTICS
ELECTRICAL-CONDUCTIVITY
PERCOLATION
MIXTURES
MEDIA
SUPERCONDUCTORS
TRANSPORT
SPHERES
Аннотация: The fractal dimension of the boundaries of clusters formed by pores and granules in polycrystalline materials is shown to be determined by the sample density and crystallite sizes. The dependence of the fractal dimension on the density has a maximum. It is shown that the maximum diamagnetic response can be obtained in a porous high-temperature superconductor with a porosity of 50-60% and small crystallite sizes.
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19.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Nikolaev S. V., Ovchinnikov S. G.
Заглавие : Effect of hole doping on the electronic structure and the Fermi surface in the Hubbard model within norm-conserving cluster pertubation theory
Место публикации : J. Exp. Theor. Phys.: MAIK Nauka-Interperiodica / Springer, 2012. - Vol. 114, Is. 1. - P.118-131. - ISSN 1063-7761, DOI 10.1134/S1063776111150143
Примечания : Cited References: 51. - This study was supported financially by the Russian Foundation for Basic Research (project nos. 10-02-90725-mob_st and 09-02-00127), Program 18.7 of the Presidium of the Russian Academy of Sciences, the Federal Target Program "Personnel" (state contract no. P891), and the integrated project no. 40 of the Siberian Branch of the Russian Academy of Sciences.
Предметные рубрики: HIGH-TEMPERATURE SUPERCONDUCTORS
NARROW ENERGY-BANDS
CORRELATED ELECTRONS
PSEUDOGAP
EVOLUTION
La2-XSRXCuO4
INSULATOR
Аннотация: The concentration dependences of the band structure, spectral weight, density of states, and Fermi surface in the paramagnetic state are studied in the Hubbard model within cluster pertubation theory with 2 x 2 clusters. Representation of the Hubbard X operators makes it possible to control conservation of the spectral weight in constructing cluster perturbation theory. The calculated value of the ground-state energy is in good agreement with the results obtained using nonperturbative methods such as the quantum Monte Carlo method, exact diagonalization of a 4 x 4 cluster, and the variational Monte Carlo method. It is shown that in the case of hole doping, the states in the band gap (in-gap states) lie near the top of the lower Hubbard band for large values of U and near the bottom of the upper band for small U. The concentration dependence of the Fermi surface strongly depends on hopping to second (t') and third (t '') neighbors. For parameter values typical of HTSC cuprates, the existence of three concentration regions with different Fermi surfaces is demonstrated. It is shown that broadening of the spectral electron density with an energy resolution typical of contemporary ARPES leads to a pattern of arcs with a length depending on the concentration. Only an order-of-magnitude decrease in the linewidth makes it possible to obtain the true Fermi surface from the spectral density. The kinks associated with strong electron correlations are detected in the dispersion relation below the Fermi level.
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20.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Korshunov M. M., Nikolaev S., Shneyder E. I., Krinitsyn A.
Заглавие : Normal and superconducting properties of cuprates in multielectron theory
Место публикации : J. Supercond. Nov. Magn. - 2013. - Vol. 26, Is. 9. - P.2831-2835. - ISSN 1557-1939, DOI 10.1007/s10948-013-2263-8
Ключевые слова (''Своб.индексиров.''): cluster perturbation theory--fermi surface reconstruction--strong electron correlations
Аннотация: We consider the doping dependence of the normal and superconducting properties of La2-x Srx CuO4 in the low energy effective model based on the ab initio LDA+GTB calculations. We have found that two quantum phase transitions (QPT) of the Lifshitz type correspond well to the experimental phase diagram. For superconducting state, we have considered both magnetic and phonon mechanisms of pairing. Finally, we compare the true Fermi surface and the spectral intensity map seen in ARPES within a new norm conserving cluster perturbation theory (NC-CPT). В© 2013 Springer Science+Business Media New York.
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