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1.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Shneyder E. I., Ovchinnikov S. G., Korshunov M. M., Nikolaev S. V.
Заглавие : Electronic structure and properties of high-Tc superconducting cuprates in the normal and superconducting phases within the LDA + GTB approach
Место публикации : JETP Letters. - 2012. - Vol. 96, Is. 5. - P.349-360. - ISSN 0021-3640, DOI 10.1134/S0021364012170146
Примечания : Cited References: 107. - This work was supported by the Russian Foundation for Basic Research (project no. 09-02-00127), by the Presidium of the Russian Academy of Sciences (program no. 20.7), by the Ministry of Education and Science of the Russian Federation (state contract nos. P891 and 16.740.12.0731), and by the Council of the President of the Russian Federation for Support of Young Scientists and Leading Scientific Schools (project nos. NSh-1044.2012.2 and MK-1168.2012.2). E.I.Sh. and M. M. K. acknowledge the support of the Dynasty Foundation.
Предметные рубрики: 2-DIMENSIONAL HUBBARD-MODEL
D-WAVE SUPERCONDUCTIVITY
HIGH-TEMPERATURE SUPERCONDUCTORS
QUANTUM CRITICAL-POINT
T-C SUPERCONDUCTOR
FERMI-SURFACE
EXCHANGE INTERACTION
SQUARE-LATTICE
BAND-STRUCTURE
COPPER OXIDES
Аннотация: Theoretical investigations of the properties of high-T c superconducting cuprates within the LDA + GTB method taking into account the magnetic and phonon pairing mechanisms have been reviewed. These properties are the concentration-dependent electronic structure, quantum phase transitions with a change in the topology of the Fermi surface, and the superconducting phase of the d_{x. - y. } symmetry.
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2.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Shneyder E. I., Spitaler J., Kokorina E. E., Nekrasov I. A., Gavrichkov V. A., Draxl C., Ovchinnikov S. G.
Заглавие : Coupling of Hubbard fermions with phonons in La2 CuO4: A combined study using density-functional theory and the generalized tight-binding method
Место публикации : J. Alloys Compd.: Elsevier, 2015. - Vol. 648. - P.258-264. - ISSN 0925-8388, DOI 10.1016/j.jallcom.2015.05.150
Примечания : Cited References: 60. - We acknowledge the stimulating discussions with V.V. Val'kov, D.M. Dzebisashvilly, M.M. Korshunov and I.S. Sandalov. E.I.S. and S.G.O. are thankful to the Russian Science Foundation (project No. 14-12-00061) for the support of the research given in Sections 2, 6 and 7. E.E.K. and I.A.N. are thankful to the State Contract No. 0389-2014-0001 and RFBR grant No. 14-02-00065 for the support of the research given in Section 5. Financial support of the research given in Sections 3 and 4 by the Austrian Federal Government (in particular from Bundesministerium fur Verkehr, Innovation und Technologie and Bundesministerium fur Wissenschaft, Forschung und Wirtschaft) represented by Osterreichische Forschungsforderungsgesellschaft mbH and the Styrian and the Tyrolean Provincial Government, represented by Steirische Wirtschaftsforderungsgesellschaft mbH and Standortagentur Tirol, within the framework of the COMET Funding Programme is gratefully acknowledged by C.D. and J.S.
Предметные рубрики: MEAN-FIELD THEORY
LINEAR-RESPONSE THEORY
CUPRATE SUPERCONDUCTORS
ELECTRONIC-STRUCTURE
CORRELATED SYSTEMS
LATTICE-DYNAMICS
BAND-STRUCTURE
LA2CUO4
MODEL
LA2-XSRXCUO4
Ключевые слова (''Своб.индексиров.''): high-temperature superconductivity--electron-phonon coupling--density-functional theory--generalized tight-binding approach
Аннотация: We present results for the electron-phonon interaction of the Γ-point phonons in the tetragonal high-temperature phase of La2 CuO4 obtained from a hybrid scheme, combining density-functional theory (DFT) with the generalized tight-binding approach. As a starting point, eigenfrequencies and eigenvectors for the Γ-point phonons are determined from DFT within the frozen phonon approach utilizing the augmented plane wave + local orbitals method. The so obtained characteristics of electron-phonon coupling are converted into parameters of the generalized tight-binding method. This approach is a version of cluster perturbation theory and takes the strong on-site electron correlations into account. The obtained parameters describe the interaction of phonons with Hubbard fermions which form quasiparticle bands in strongly correlated electron systems. As a result, it is found that the Γ-point phonons with the strongest electron-phonon interaction are the A2u modes (236 cm-1, 131 cm-1 and 476 cm-1). Finally it is shown, that the single-electron spectral-weight redistribution between different Hubbard fermion quasiparticles results in a suppression of electron-phonon interaction which is strongest for the triplet Hubbard band with z oriented copper and oxygen electrons. © 2015 Elsevier B.V. All rights reserved.
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3.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ding Y., Haskel D., Ovchinnikov S. G., Tseng Y. C., Orlov Y. S., Lang J. C., Mao H. K.
Заглавие : Novel pressure-induced magnetic transition in magnetite (Fe(3)O(4))
Разночтения заглавия :авие SCOPUS: Novel pressure-induced magnetic transition in magnetite (Fe3O4)
Место публикации : Phys. Rev. Lett.: AMER PHYSICAL SOC, 2008. - Vol. 100, Is. 4. - Ст.45508. - ISSN 0031-9007, DOI 10.1103/PhysRevLett.100.045508
Примечания : Cited References: 39
Предметные рубрики: MULTIPLE-SCATTERING THEORY
X-RAY DICHROISM
LOWER MANTLE
VERWEY TRANSITION
K-EDGE
CIRCULAR-DICHROISM
SPIN TRANSITION
BAND-STRUCTURE
IRON
FE
Ключевые слова (''Своб.индексиров.''): emission spectroscopy--magnetoelectronics--pressure effects--synchrotron radiation--diamond anvil cell--magnetic transition--x-ray magnetic circular dichroism--magnetite
Аннотация: Fe K-edge x-ray magnetic circular dichroism of magnetite (Fe(3)O(4)) powders was measured with synchrotron radiation under variable pressure and temperature conditions in diamond anvil cell. The magnetic dichroism was observed to decrease discontinuously by similar to 50% between 12 and 16 GPa, independent of temperature. The magnetic transition is attributed to a high-spin to intermediate-spin transition of Fe(2+) ions in the octahedral sites and could account for previously observed structural and electrical anomalies in magnetite at this pressure range. The interpretation of x-ray magnetic circular dichroism data is supported by x-ray emission spectroscopy and theoretical cluster calculations.
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4.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kazak N. V., Ovchinnikov S. G., Abd-Elmeguid M. M., Ivanova N. B.
Заглавие : Electronic properties of Fe1-xVxBO3 at ambient conditions and at high pressure
Разночтения заглавия :авие SCOPUS: Electronic properties of Fe1-xVx-BO3 at ambient conditions and at high pressure
Место публикации : J. Phys.: Condens. Matter: IOP PUBLISHING LTD, 2005. - Vol. 17: 2nd International Symposium on Physics of Solids Under High Pressure Using Nuclear Probes (JUL 20-24, 2004, Cologne, GERMANY), Is. 11. - P.S795-S800. - ISSN 0953-8984, DOI 10.1088/0953-8984/17/11/008
Примечания : Cited References: 16
Предметные рубрики: FEBO3 SINGLE-CRYSTALS
SOLID-SOLUTIONS
BAND-STRUCTURE
TRANSITION
MOSSBAUER
MAGNETIZATION
MODEL
VBO3
Ключевые слова (''Своб.индексиров.''): electronic properties--ferrimagnetic materials--high pressure effects--high temperature superconductors--metal insulator transition--single crystals--superconductivity--thermal effects--carrier localization--correlation effects--critical pressure--semiconducting behavior--oxide superconductors
Аннотация: We present the results of an in-plane resistivity study of the solid solutions Fe1-xVxBO3. The measurements were made on single crystals with concentration x = 0.02, 0.13, 0.18, 0.3, 0.95, 1.0 in the temperature range 220-600 K. Semiconducting behaviour for samples with x = 0.13 was found. Mott variable-range-hopping transport rho(T) = rho(0)exp(T*/T)(alpha) has been observed with alpha = 1/4 at T 290 K, suggesting carrier localization. Above this temperature the activation-type conductivity, with activation energies, E-a, about 1 eV for all samples, is observed. The possible electronic states and band structure of Fe1-xVx BO3 crystals are discussed in the different pressure ranges: P P-c(Fe), p(c)(Fe) p p(c)(V) P P-c(V) where p(c)(Fe) P-c(V) are the critical pressure values for FeBO3 and VBO3, respectively.
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5.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G.
Заглавие : The mechanism of the electronic transition in ferroborates under high pressure
Место публикации : J. Phys.: Condens. Matter: IOP PUBLISHING LTD, 2005. - Vol. 17: 2nd International Symposium on Physics of Solids Under High Pressure Using Nuclear Probes (JUL 20-24, 2004, Cologne, GERMANY), Is. 11. - P.S743-S751. - ISSN 0953-8984, DOI 10.1088/0953-8984/17/11/003
Примечания : Cited References: 20
Предметные рубрики: STRUCTURAL PHASE-TRANSITION
MAGNETIC COLLAPSE
OPTICAL-SPECTRA
BAND-STRUCTURE
FEBO3
MODEL
Ключевые слова (''Своб.индексиров.''): carrier concentration--correlation methods--electron transitions--high pressure effects--magnetic moments--mathematical models--metal insulator transition--crystal field--electron correlations--electronic transition--ferroborates--ferromagnetic materials
Аннотация: A novel mechanism for the insulator-semiconductor transition and magnetic collapse in FeBO3 is proposed in the framework of the multielectron model with account taken of strong electron correlations. The electronic transition results from the crossover of the high spin and low spin Fe3+ states induced by the crystal field increasing with pressure. In the high pressure phase a semiconductor-metal transition is expected.
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6.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zabluda V. N., Ovchinnikov S. G., Potseluliko A. M., Kharlamova S. A.
Заглавие : Optical properties and electronic structure of rare-earth ferroborates
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2005. - Vol. 47, Is. 3. - P489-494. - ISSN 1063-7834, DOI 10.1134/1.1884710
Примечания : Cited References: 19. - This work was supported by the Russian Foundation for Basic Research (project no. 03-02-16268) and the program of the Department of Physical Sciences of the Russian Academy of Sciences "Strongly Correlated Electrons"
Предметные рубрики: TRIGONAL GDFE3(BO3)(4)
MAGNETIC-PROPERTIES
BAND-STRUCTURE
FEBO3
ABSORPTION
Аннотация: The optical absorption spectra of single-crystal ferroborate GdFe3(BO3)(4) and GdFe2.1Ga0.9(BO3)(4) are measured and interpreted. It is found that the absorption edge and the absorption bands A, B, and C observed below the edge are close to those for FeBO3. A many-electron model of the band structure of GdFe3(BO3)(4) is suggested including strong electron correlations between the iron d states. It is shown that GdFe3(BO3)(4) has a charge-transfer dielectric gap. A rise in pressure is predicted to result in a crossover between the high-spin and low-spin states of the Fe ion, collapse of the magnetic moment, a weakening of Coulomb correlations, an abrupt reduction in the energy gap, and an insulator-semiconductor transition. (c) 2005 Pleiades Publishing, Inc.
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7.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gavriliuk A. G., Trojan I. A., Lyubutin I. S., Ovchinnikov S. G., Sarkissian V. A.
Заглавие : High-pressure magnetic properties and P-T phase diagram of iron borate
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 2005. - Vol. 100, Is. 4. - P688-696. - ISSN 1063-7761, DOI 10.1134/1.1926429
Примечания : Cited References: 24
Предметные рубрики: FEBO3 SINGLE-CRYSTALS
NUCLEAR-RESONANCE
BAND-STRUCTURE
TRANSITION
TEMPERATURE
SCATTERING
Ключевые слова (''Своб.индексиров.''): antiferromagnetic materials--diamonds--ferromagnetic materials--high pressure effects--low temperature effects--magnetic moments--magnetic properties--magnetization--phase diagrams--powders--single crystals--synchrotron radiation--diamond anvil cells--electronic transition--iron borate--nuclear forward scattering (nfs)--iron compounds
Аннотация: The high-pressure magnetic states of iron borate (FeBO3)-Fe-57 single-crystal and powder samples have been investigated in diamond anvil cells by nuclear forward scattering (NFS) of synchrotron radiation at different temperatures. In the low-pressure (0 < P < 46 GPa) antiferromagnetic phase, an increase of the Neel temperature from 350 to 595 K induced by pressure was found. At pressures 46-49 GPa, a transition from the antiferromagnetic to a new magnetic state with a weak magnetic moment (magnetic collapse) was discovered. It is attributed to the electronic transition in Fe3+ ions from the high-spin 3d(5) (S = 5/2, (6)A(1g)) to the low-spin (S = 1/2, T-2(2g)) state (spin crossover) due to the insulator-semiconductor-type transition with extensive suppression of strong d-d electron correlations. At low temperatures, NFS spectra of the high-pressure phase indicate magnetic correlations in the low-spin system with a magnetic ordering temperature of about 50 K. A tentative magnetic P-T phase diagram of FeBO3 is proposed. An important feature of this diagram is the presence of two triple points where magnetic and paramagnetic phases of the high-spin and low-spin states coexist. © 2005 Pleiades Publishing, Inc.
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8.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gavriliuk A. G., Kharlamova S. A., Lyubutin I. S., Troyan I. A., Ovchinnikov S. G., Potseluiko A. M., Eremets M. I., Boehler R.
Заглавие : Structural and electronic transitions in gadolinium iron borate GdFe3(BO3)(4) at high pressures
Место публикации : JETP Letters. - 2004. - Vol. 80, Is. 6. - P.426-432. - ISSN 0021-3640, DOI 10.1134/1.1830662
Примечания : Cited References: 20
Предметные рубрики: TRIGONAL GDFE3(BO3)(4)
RM(3)(BO3)(4) CRYSTALS
OPTICAL-SPECTRA
BAND-STRUCTURE
FEBO3
GROWTH
Аннотация: The optical properties and structure of gadolinium iron borate GdFe3(BO3)(4) crystals are studied at high pressures produced in diamond-anvil cells. X-ray diffraction data obtained at a pressure of 25.6 GPa reveal a first-order phase transition retaining the trigonal symmetry and increasing the unit cell volume by 8%. The equation of state is obtained and the compressibility of the crystal is estimated before and after the phase transition. The optical spectra reveal two electronic transitions at pressures similar to26 GPa and similar to43 GPa. Upon the first transition, the optical gap decreases jumpwise from 3.1 to similar to2.25 eV. Upon the second transition at P = 43 GPa, the optical gap deceases down to similar to0.7 eV, demonstrating a dielectric-semiconductor transition. By using the theoretical model developed for a FeBO3 crystal and taking into account some structural analogs of these materials, the anomalies of the high-pressure optical spectra are explained. (C) 2004 MAIK "Nauka/Interperiodica".
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9.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Borisov A.A., Gavrichkov V. A., Ovchinnikov S. G.
Заглавие : Temperature and concentration dependences of the electronic structure of copper oxides in the generalized tight binding method
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 2003. - Vol. 97, Is. 4. - P773-780. - ISSN 1063-7761, DOI 10.1134/1.1625067
Примечания : Cited References: 25
Предметные рубрики: SUPERCONDUCTING-GAP ANISOTROPY
BAND-STRUCTURE
FERMI-SURFACE
NORMAL-STATE
BI2SR2CACU2O8+DELTA
EVOLUTION
Ключевые слова (''Своб.индексиров.''): doping (additives)--electron transitions--electronic structure--fermi level--fermi surface--electron correlations--pseudogap--tight binding method--valence band--copper oxides
Аннотация: The electronic structure of p-type doped HTSC cuprates is calculated by explicitly taking into account strong electron correlations. The smooth evolution of the electronic structure from undoped antiferromagnetic to optimally and heavily doped paramagnetic compositions is traced. For a low doping level, in-gap impurity-type states are obtained, at which the Fermi level is pinned in the low-doping region. These states are separated by a pseudogap from the valence band. The Fermi surfaces calculated for the paramagnetic phase for various concentrations of holes are in good agreement with the results of ARPES experiments and indicate a gradual change in the Fermi surface from the hole type to the electron type. (C) 2003 MAIK "Nauka/Interperiodica".
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Korshunov M. M., Ovchinnikov S. G.
Заглавие : The effective Hamiltonian of the singlet-triplet model for copper oxides
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2001. - Vol. 43, Is. 3. - P416-419. - ISSN 1063-7834, DOI 10.1134/1.1356113
Примечания : Cited References: 15
Предметные рубрики: HIGH-TC SUPERCONDUCTORS
BAND-STRUCTURE
LA2-XSRXCUO4
MECHANISM
SYMMETRY
SPECTRUM
Аннотация: The effective Hamiltonian for a realistic multiband p-d model is developed. In the case of electron doping, the Hamiltonian coincides with that for the standard t-J model. For hole doping, the singlet-triplet t-J model takes place. (C) 2001 MAIK "Nauka/Interperiodica".
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 1-10    11-15 
 

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