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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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Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Ovchinnikov S. G.
Заглавие : Comparison of electronic structure, magnetic mechanism, and symmetry of pairing in ruthenates and cuprates
Место публикации : Ruthenate and rutheno-cuprate materials: unconventional superconductivity, magnetism and quantum phase transitions. Ser. lecture notes in physics: Springer Verlag, 2002. - Vol. 603: International Conference on Ruthenate and Rutheno-Cuprate Materials (OCT 25-27, 2001, VIETRI SUL MARE, ITALY). - P.239-255. - ISBN 0075-8450. - ISBN 3-540-44275-8
Примечания : Cited References: 48
Предметные рубрики: METAL-INSULATOR-TRANSITION
SUPERCONDUCTOR SR2RUO4
LAYERED PEROVSKITE
BAND-STRUCTURE
CORRELATED ELECTRONS
MOTT TRANSITION
COPPER OXIDES
HUBBARD-MODEL
RUSR2GDCU2O8
CA2-XSRXRUO4
Аннотация: A generalized tight-binding (GTB) method is developed to calculate quasi-particle band structure with explicit account for strong electronic correlations. The GTB method combines exact diagonalization of the multi-orbital P-d model Hamiltonian within the unit cell and the perturbation theory in the Hubbard X-operators form for the inter-cell hopping and interactions. For undoped cuprates we obtain the valence band structure in excellent agreement with ARPES data, evolution of the band structure with doping with an in-gap state at small doping, impurity-like band at higher doping to optimally doped metal. The effective low-energy Hamiltonian has the form of singlet-triplet t-J model. For ruthenates the t-J-I model is proposed with both antiferromagnetic J and ferromagnetic I couplings. In the strong correlation limit, the mean-field theory of superconductivity results in d-wave singlet pairing mediated by J (cuprates) and p-wave triplet one mediated by I (ruthenates) with ratio T-c((d))/T-c((p)) similar to 100 due to the different symmetry of the gap. The competition of ferromagnetic and antiferromagnetic order in rutheno-cuprates is also discussed.
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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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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G.
Заглавие : Generalized tight binding method for SCES as a perturbative realization of the exact Lehmann representation
Коллективы : International Conference on Strongly Correlated Electron Systems
Место публикации : Acta Phys. Pol. B. - 2003. - Vol. 34, Is. 2. - P.431-434. - ISSN 0587-4254
Примечания : Cited References: 12
Предметные рубрики: BAND-STRUCTURE
MODEL
SR2CUO2CL2
Аннотация: Both perturbation approach in the Hubbard operator representation and the exact Lehmann representation proves that the electron quasiparticle in SCES has spin S = 1/2, electric charge e, QP energy and QP spectral weight split over various QP bands. General theory and its application to the hole doped CuO2 layer are considered.
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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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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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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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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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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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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kazak N. V., Potseluyko A. M., Ovchinnikov S. G., Alexandrovsky A. S., Chernov V. A., Rudenko V. V.
Заглавие : EXAFS study of Fe1-xVxBO3 system
Разночтения заглавия :авие SCOPUS: EXAFS study of Fe1 - x Vx BO3 system
Место публикации : Physica B: ELSEVIER SCIENCE BV, 2006. - Vol. 378-80: International Conference on Strongly Correlated Electron Systems (SECES 05) (JUL 26-30, 2005, Vienna, AUSTRIA). - P327-329. - ISSN 0921-4526, DOI 10.1016/j.physb.2006.01.119
Примечания : Cited References: 10
Предметные рубрики: MANY-ELECTRON MODEL
CALCITE STRUCTURE
BAND-STRUCTURE
FEBO3
VBO3
TRANSITION
CRBO3
Ключевые слова (''Своб.индексиров.''): strongly correlated electron systems--x-ray absorption spectra--transition-metal compounds--strongly correlated electron systems--transition-metal compounds--x-ray absorption spectra--absorption--atomic force microscopy--solid solutions--transition metal compounds--x ray analysis--strongly correlated electron systems--x-ray absorption spectra--iron compounds
Аннотация: The room-temperature EXAFS measurements have been made on FeBO3 and VBO3, as well as on Fe1-xVxBO3 series with concentration x=0.13,0.3, and 0.95. The first-shell Me-O bond lengths deduced from EXAFS have shown a compositional independence. It has been found that Fe1-xVxBO3 forms solid solutions with random distribution of Fe3+ and V3+ ions. (c) 2006 Elsevier B.V. All rights reserved.
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