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Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Kuz'min V. I., Nikolaev S. V., Ovchinnikov S. G.
Заглавие : Anomalous spectral properties of strongly correlated systems within the cluster perturbation theory
Коллективы : Российская академия наук, Уральское отделение РАН, Институт физики металлов им. М. Н. Михеева Уральского отделения РАН, Уральский федеральный университет им. первого Президента России Б.Н. Ельцина, Российский фонд фундаментальных исследований, Euro-Asian Symposium "Trends in MAGnetism", "Trends in MAGnetism", Euro-Asian Symposium
Место публикации : Euro-asian symposium "Trends in magnetism" (EASTMAG-2019): Book of abstracts/ чл. конс. ком.: S. G. Ovchinnikov, N. V. Volkov [et al.] ; чл. прогр. ком. D. M. Dzebisashvili [et al.]. - 2019. - Vol. 2. - Ст.I.P9. - P.151-152. - ISBN 978-5-9500855-7-4 (Шифр В33/E12-125657784)
Примечания : Cited References: 4. - The reported study was funded by Russian Foundation for Basic Research (RFBR) according to the research project no. 18-32-00256, RFBR and Government of Krasnoyarsk Territory, Krasnoyarsk Regional Fund of Science to the research project: “18-42-240017 Features of electron-phonon coupling in high-temperature superconductors with strong electron correlations” and the research project: “18-42-243004 New thermoelectric materials based on multi-scale spatially inhomogeneous substituted rare-earth cobalt oxides and the Ruddlesden-Popper phases”
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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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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 сборника (однотомник)
Шифр издания :
Автор(ы) : Korshunov M. M., Nikolaev S. V., Togushova Yu. N.
Заглавие : Cluster perturbation approach to iron-based superconductors
Коллективы : Quantum in Complex Matter: Superconductivity, Magnetism and Ferroelectricity, International conference
Место публикации : Quant. in Complex Matter: Supercond., Magnet. and Ferroelectr.: book of abstracts/ ed. A. Bianconi. - Rome, 2016. - P.148. - ISBN 978-88-6683-055-9
Примечания : References: 8. - This work was partially supported by the RFBR (grant 16-02-00098)
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ivantsov I. D., Ovchinnikov S. G.
Заглавие : Cluster perturbation theory for 2d ising model
Место публикации : J. Sib. Fed. Univ. Math. Phys. - 2015. - Vol. 8, Is. 1. - P.31-37. - ISSN 1997-1397; Журн. СФУ. Сер. "Математика и физика"
Примечания : Cited References: 5. - The authors are grateful to Sergey V. Nikolaev for useful discussions and President of Russia, grant nsh-2886.2014.2
Ключевые слова (''Своб.индексиров.''): cluster perturbation theory--ising model--x-operators--модель изинга--кластерная теория возмущений--х-операторы
Аннотация: This paper deals with 2d Ising model in the scope of cluster perturbation theory. Ising model is defined on a two-dimensional square lattice, the amount of nearest neighbors z=4. Lattice is divided into clusters of a given size and a complete set of energy eigenvalues and eigenvectors of the cluster is defined by the diagonalization method. On the basis of this, Hubbard operators are constructed and Green function is calculated, taking into account intercluster interactions according to perturbation theory, it allows us to obtain the dependence of the magnetization on the temperature in the Hubbard-I approximation. Obtained results are compared with the exact solution of the two-dimensional Ising model.В настоящей работе проводится исследование двумерной модели Изинга в рамках кластерной теории возмущений. Модель Изинга задана на двумерной квадратной решетке с числом ближайших соседей z=4. Решетка разбивается на кластеры заданного размера и методом точной диагонализации определяется полный набор собственных значений энергии и собственных векторов кластера. На этом базисе строятся операторы Хаббарда и вычисляется функция Грина с учетом межкластерных взаимодействий по теории возмущений, позволяющая получить зависимость намагниченности от температуры в приближении Хаббард-I. Полученные результаты сравниваются с точным решением двумерной модели Изинга.
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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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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Krinitsyn A., Nikolaev S., Ovchinnikov S. G.
Заглавие : Cluster size and shape effect on the electronic structure of the Hubbard model within the norm-conserving cluster perturbation theory
Коллективы : Siberian Federal University [F-11]; Presidium of RAS Program [20.7]; [NSh-1044.2012.2]; [MK-1168.2012.2]
Место публикации : J. Supercond. Nov. Magn.: Springer, 2014. - Vol. 27, Is. 4. - P.955-963. - ISSN 1557-1939, DOI 10.1007/s10948-013-2418-7. - ISSN 1557-1947
Примечания : Cited References: 59. - This work was supported by Grants NSh-1044.2012.2 and MK-1168.2012.2, Siberian Federal University: Grant F-11, and the Presidium of RAS Program 20.7.
Предметные рубрики: NARROW ENERGY-BANDS
CUPRATE SUPERCONDUCTORS
PHOTOEMISSION SPECTRA
PSEUDOGAP
ANTIFERROMAGNET
EXCITATIONS
EVOLUTION
SYSTEMS
PHASE
STATE
Ключевые слова (''Своб.индексиров.''): cluster perturbation theory--hubbard model--strong correlations--density of states--fermi surface
Аннотация: Within a new norm-conserving approach to the cluster perturbation theory (CPT) for the 2d Hubbard model we study the effect of the cluster size and shape on the electronic structure. We have compared two type of clusters, 4-cluster (2x2) and 5-cluster (cruciform of 5 atoms). With 4-cluster we can treat exactly the first and second neighbours correlations, C (1) and C (2). With 5-cluster the third neighbour correlations C (3) are also treated exactly. The band structure in the CPT with 4- and 5-clusters differs remarkably. The quasiparticle spectral weight map for 5-clusters is very similar to the Quantum Monte Carlo (QMC) and the variational CPT data. With increasing doping, small hole Fermi surface transforms into conventional Fermi-liquid type large Fermi surface through Lifshitz quantum phase transitions.
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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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10.

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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11.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kuz'min V. I., Nikolaev S. V., Ovchinnikov S. G.
Заглавие : Comparison of the electronic structure of the Hubbard and t - J models within the cluster perturbation theory
Коллективы : RFBR [13-02-01395-a, 14-02-31677-mol-a, 14-02-00186-a]; Ministry of Education and Science of Russia [3085, SibFU 2014 GF-2]; [NSh-2886.2014.2]
Место публикации : Phys. Rev. B: American Physical Society, 2014. - Vol. 90, Is. 24. - Ст.245104. - ISSN 1098-0121, DOI 10.1103/PhysRevB.90.245104. - ISSN 1550-235X
Примечания : Cited References: 37. - This work is supported by RFBR (Grants No. 13-02-01395-a, No. 14-02-31677-mol-a, and No. 14-02-00186-a), the Ministry of Education and Science of Russia (Government Contract No. 3085, SibFU 2014 GF-2), and a grant of the Russian President (Grant No. NSh-2886.2014.2).
Предметные рубрики: FERMION SYSTEMS
SUPERCONDUCTIVITY
METAL
Аннотация: Electronic dispersion and density of states (DOS) have been calculated for the Hubbard model and the t−J and t−J∗ models with three-site correlated hopping by the cluster perturbation theory. We have found a rather strong quantitative difference both in dispersion and DOS at all doping for the Hubbard and t−J models at the energy scale ω≳t. The three-site correlated hopping addition results in an almost negligible difference for the Hubbard and t−J∗ models. Close to the Fermi energy, at the scale ω≲J, the electronic structure of all three models is similar. We have found the line of zeros of the Green function for the t−J model that has been previously obtained for the Hubbard model by cellular dynamical mean-field theory calculations.
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12.

Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Kuz'min V. I., Nikolaev S. V., Ovchinnikov S. G.
Заглавие : Comparison of the electronic structure of the Hubbard and t-J models within the cluster perturbation theory
Коллективы : "Фундаментальные проблемы высокотемпературной сверхпроводимости", Международная конференция, Российская академия наук, Физический институт им. П.Н. Лебедева РАН, Научный совет по физике конденсированного состояния РАН, Научный совет по физике низких температур РАН
Место публикации : Пятая Междунар. конф. "Фундаментал. проблемы высокотемператур. сверхпроводимости" (ФПС’15): сборник расширенных тезисов. - М.: ФИАН, 2015. - Ст.M7. - С. 58-59
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13.

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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14.

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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15.

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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16.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kuz'min V. I., Nikolaev S. V., Ovchinnikov S. G.
Заглавие : Effect of canted antiferromagnetic order on the electronic structure in the t–J* model within the cluster perturbation theory
Место публикации : J. Exp. Theor. Phys.: Maik Nauka-Interperiodica Publishing, 2016. - Vol. 123, Is. 3. - P.511-519. - ISSN 10637761 (ISSN), DOI 10.1134/S1063776116090065
Примечания : Cited References: 50. - We are grateful to V.V. Val’kov for stimulating discussions. This work was supported by the Russian Science Foundation (project no. 14-12-00061)
Ключевые слова (''Своб.индексиров.''): antiferromagnetism--electronic structure--high temperature superconductors--magnetic fields--antiferromagnetic orderings--cluster perturbation theories--electron-doping--external fields--external magnetic field--non-monotonic dependence--short-range correlations--spectral weight--perturbation techniques
Аннотация: The electronic structure in the two-dimensional t–J* model with canted antiferromagnetic order in an external magnetic field has been calculated within the cluster perturbation theory. In zero external field, the evolution of the Fermi surface with n-type doping has been obtained in good agreement with experimental data on cuprate superconductors. It has been shown that the inclusion of short-range correlations can result in a nonmonotonic dependence of the spectral weight distribution at the Fermi level on the external magnetic field. In contrast to the case of electron doping, such changes in the case of hole doping can be expected at experimentally achievable fields. © 2016, Pleiades Publishing, Inc.
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17.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zobov V. E., Lundin A. A.
Заглавие : Effect of degradation processes caused by a small perturbation on the growth of the average cluster size of correlated spins in multiple quantum NMR spectroscopy of solids
Место публикации : Appl. Magn. Reson. - 2021. - Vol. 52. Is. 7. - P.879–892. - ISSN 09379347 (ISSN), DOI 10.1007/s00723-021-01342-1
Примечания : Cited References: 33. - The study is funded by the Ministry of Science and Higher Education of the Russian Federation in the framework of the State assignment, State registration number AAAA-A19-119012890064-7
Аннотация: Multiple quantum (MQ) NMR spectroscopy of solids allows one to observe the growth and decay of multispin correlations. As a rule, the average size of the cluster of correlated spins is extracted from the width of the MQ spectrum. In the present article, the size distribution of such clusters is explored. To obtain the above distribution, the solutions for the amplitudes of the decomposition over complete sets of orthogonal operators for the two different models were used. By means of these models, we have taken into account the dependence of cluster degradation (the degradation of a cluster means, e.g., destruction of correlations in cluster or loss of particles in it) through two positions. The first one defines by the cluster size while the second one depends on the MQ coherence order of the cluster. It is shown that in dependence of the relation the rates of these degradation processes, the width of the MQ spectrum carries different information. If the first process is faster that the second one, then the width of the MQ spectrum is still determined by the average cluster size. When the velocity ratio becomes inverse, the width of the MQ spectrum takes on a smaller value, which is a consequence of the faster degradation of the MQ spectrum components with large orders of coherence.
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18.

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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19.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kuz'min V. I., Nikolaev S. V., Ovchinnikov S. G.
Заглавие : Effect of short-range correlations on spectral properties of doped Mott insulators
Место публикации : J. Supercond. Novel Magn. - 2019. - Vol. 32, Is. 7. - P.1909-1919. - ISSN 15571939 (ISSN) , DOI 10.1007/s10948-018-4927-x
Примечания : Cited References: 81. - The reported study was funded by RFBR according to the research project no. 18-32-00256 (all the results except correlation functions calculated using 4 × 4 clusters). The study also was funded by the Presidium RAS program no. 12 “Fundamental problems of high temperature superconductivity” (research project 0356-2018-0063); “BASIS” Foundation for Development of Theoretical Physics and Mathematics; RFBR according to the research project no. 16-02-00098; RFBR and Government of Krasnoyarsk Territory, Krasnoyarsk Regional Fund of Science, the research project: “18-42-240017 Features of electron-phonon coupling in high-temperature superconductors with strong electron correlations” and the research project 18-42-243004.
Аннотация: In the framework of the cluster perturbation theory for the 2D Hubbard and Hubbard-Holstein models at low hole doping, we have studied the effect of local and short-range correlations in strongly correlated systems on the anomalous features in the electronic spectrum by investigating the fine structure of quasiparticle bands. Different anomalous features of spectrum are obtained as the result of intrinsic properties of strongly correlated electron and polaron bands in the presence of short-range correlations. Particularly, features similar to the electron-like Fermi-pockets of cuprates at hole doping p ∼ 0.1 are obtained without ad hoc introducing a charge density wave order parameter within the Hubbard model in a unified manner with other known peculiarities of the pseudogap phase like Fermi-arcs, pockets, waterfalls, and kink-like features. The Fermi surface is mainly formed by dispersive quasiparticle bands with large spectral weight, formed by coherent low-energy exications. Within the Hubbard-Holstein model at moderate phonon frequencies, we show that modest values of local electron-phonon interaction are capable of introducing low-energy kink-like features and affecting the Fermi surface by hybridization of the fermionic quasiparticle bands with the Franck-Condon resonances.
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20.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Nikolaev S. V., Orlov Yu. S., Dudnikov V. A.
Заглавие : Electronic Structure and Conductivity of a Disordered A1–xBx Binary Alloy in the Cluster Approach for the Hubbard Model
Место публикации : J. Exp. Theor. Phys. - 2020. - Vol. 131, Is. 5. - P.823-837. - ISSN 10637761 (ISSN), DOI 10.1134/S1063776120100131
Примечания : Cited References: 27. - This study was supported by the Foundation “Basis” for development of theoretical physics and mathematics, Russian Foundation for Basic Research (project no. 19-03-00017), Government of Krasnoyarsk Territory and Krasnoyarsk Regional Fund of Science according to the research project “Electronic correlation effects and multiorbital physics in iron-based materials and cuprates” (no. 19-42-240007) and research project “Features of electron-phonon coupling in high-temperature superconductors with strong electronic correlations” (no. 18-42-240017)
Аннотация: We propose a method for calculating the electronic band structure of disordered systems with strong electron correlations. Various approaches to the description of electrical conductivity of disordered systems are considered. Calculations are based on determining the one-particle Green function of the system, which is averaged over different configurations of a cluster, on the Boltzmann formalism, and the Kubo linear response theory. As the basic model, we use the Hubbard model for an A –xBx binary alloy.
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