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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Pchelkina Z. V., Kondakov D. E., Anisimov V. I., Leonov I. V., Gavrichkov V. A. , Ovchinnikov S. G.
Заглавие : Ab initio calculation of the parameters and band structure of the multiband p-d model for La2CuO4
Место публикации : The Physics of Metals and Metallography. - 2006. - Т. 101, №1 suppl. - С. P. - ISSN 0031-918X, DOI 10.1134/S0031918X06130059. - ISSN 1531-8672(eissn)
Примечания : Библиогр.: 9. - Joint Integration Pro gram of the Siberian and Ural Divisions of the Russian Academy of Sciences (no. 22); the RFBR–GFEN (grant no. 03-02-39024); the Russian Foundation for Basic Research (grant nos. 04-02-16096 and 03-02-16124); the Siberian Division of the Russian Academy of Sciences, Strongly Correlated Electron Systems Pro gram; and INTAS (grant no. 01-0654).
Аннотация: In this paper, we proposed ab initio calculation of hopping parameters for La2CuO4. The Wannier function projection procedure of obtaining a small Hamiltonian in real space for different sets of bands of inter est was used. The importance of taking into account Cu and apical Oa pz orbitals is shown. The param eters obtained are used to calculate the band structure of undoped La2CuO4 in the framework of the multiband p–d model in the regime of strong electron correlations.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Korshunov M. M., Ovchinnikov S. G., Gavrichkov V. A., Nekrasov I. A., Pchelkina Z. V., Anisimov V. I.
Заглавие : Application of the new LDA plus GTB method for the band structure calculation of n-type cuprates
Разночтения заглавия :авие SCOPUS: Application of the new LDA+GTB method for the band structure calculation of n-type cuprates
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). - P459-460. - ISSN 0921-4526, DOI 10.1016/j.physb.2006.01.340
Примечания : Cited References: 11
Предметные рубрики: SUPERCONDUCTIVITY
PARAMETERS
DENSITY
Ключевые слова (''Своб.индексиров.''): strongly correlated electron systems--superconductivity--n-type cuprates--n-type cuprates--strongly correlated electron systems--superconductivity--electronic structure--hamiltonians--mathematical models--oxide superconductors--perturbation techniques--intercluster hopping--n-type cuprates--strongly correlated electron systems--band structure
Аннотация: A novel hybrid scheme is proposed and applied for band structure calculations of undoped n-type cuprate Nd2CuO4. The ab initio LDA calculation is used to obtain single electron and Coulomb parameters of the multiband Hubbard-type model. In strong correlation regime the electronic structure within this model is calculated by the generalized tight-binding (GTB) method, that combines the exact diagonalization of the model Hamiltonian for a small cluster with perturbation treatment of the intercluster hopping and interactions. For Nd2CuO4, this scheme results in charge transfer insulator with value of the gap and band dispersion in agreement to the experimental data. (c) 2006 Elsevier B.V. All rights reserved.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Balaev A. D., Gavrichkov V. A., Ovchinnikov S. G.
Заглавие : Quantum oscillations of resistance and magnetization in the degenerate semiconductor n-HgCr2Se4
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 1998. - Vol. 86, Is. 5. - P1026-1029. - ISSN 1063-7761, DOI 10.1134/1.558549
Примечания : Cited References: 6
Аннотация: In the magnetic field range Delta H = 8-60 kOe we observed and studied the anomalous oscillations in the magnetic field dependence of the resistance and magnetization of single crystals of n-HgCr2Se4. The absence of periodicity in 1/H in the Delta H = 8-20 kOe range can be explained by the non-Fermi-liquid behavior of the electron subsystem and agrees with the theory of the de Haas-van Alphen in systems with intermediate valence. In stronger fields, Delta H = 20-60 kOe, the amplitude of the fundamental harmonic decreases, with the number and amplitude of the higher-order harmonics increasing, As a result, noise is superimposed on the signal as magnetic field strength grows. The temperature dependence of the magnetization is the sum of the monotonic spin-wave contribution and the oscillating part. (C) 1998 American Institute of Physics. [S1063-7761(98)02205-7].
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Borisov A. A., Gavrichkov V. A., Ovchinnikov S. G.
Заглавие : Doping dependence of the band structure and chemical potential in cuprates by the generalized tight-binding method
Коллективы : International Conference on Modern Problems in Superconductivity
Место публикации : Mod. Phys. Lett. B/ International Conference on Modern Problems in Superconductivity (3 ; 2002 ; Sept. ; 9-14 ; Yalta, Ukrain). - 2003. - Vol. 17, Is. 10-12. - P.479-486. - ISSN 0217-9849, DOI 10.1142/S0217984903005500
Примечания : Cited References: 12
Предметные рубрики: CORRELATED ELECTRONS
SUPERCONDUCTIVITY
OXIDES
Аннотация: Quasiparticle band structure in hole doped CuO2 layer is calculated with account for strong electron correlations in the framework of multiband p-d model. For undoped layer we obtain the charge-transfer antiferromagnetic insulator. With doping unusual impurity-like quasiparticle appears at the top of the valence band with spectral weight proportional to doping concentration. In the overdoped regime the band structure in the paramagnetic phase results in the doping dependent Fermi surface in agreement to ARPES data.
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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) : Gavrichkov V. A., Ivanova N. B., Ovchinnikov S. G., Balaev A. D., Aminov T. G., Shabunina G. G., Chernov V. K., Petukhov M. V.
Заглавие : Comparison of negative magnetoresistance mechanisms in manganese perovskites and chromium spinels
Место публикации : Phys. Solid State: AMER INST PHYSICS, 1999. - Vol. 41, Is. 10. - P1652-1655. - ISSN 1063-7834, DOI 10.1134/1.1131064
Примечания : Cited References: 17
Предметные рубрики: ANISOTROPIC MAGNETORESISTANCE
TRANSPORT-PROPERTIES
THIN-FILMS
ALLOYS
Аннотация: A transition of the field dependence of the electrical resistivity from a square law (similar to H-2) above T-c to a linear function (similar to H) below T-c is observed in the degenerate ferromagnetic semiconductor HgCr2Se4(n). Together with the large negative magnetoresistance, these magnetoelectric effects correspond to effects observed in the perovskite-type oxides La1-xCaxMnOdelta. Inasmuch as the undoped semiconductor HgCr2Se4 is a ferromagnet with approximately the same critical temperature as the doped semiconductor and in view of the total lack of data on the Jahn-Teller effect in this compound, we infer that our results cast doubt on existing hypotheses (polaron and binary exchange) regarding the origin of the giant magnetoresistance in La1-xCaxMnOdelta. Impurity sd scattering is discussed as a possible magnetoresistance mechanism for both compounds. (C) 1999 American Institute of Physics. [S1063-7834(99)01710-4].
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gavrichkov V. A., Ovchinnikov S. G., Nekrasov I. A., Kokorina E. E., Pchelkina Z. V.
Заглавие : Comparison of the single-electron and many-electron mechanisms of the concentration dependence of the HTSC cuprate band structure
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2007. - Vol. 49, Is. 11. - P2052-2057. - ISSN 1063-7834, DOI 10.1134/S1063783407110066
Примечания : Cited References: 12. - This work was supported by the Russian Foundation for Basic Research (project nos. 05-02-16301, 05-02-17244, 06-02-90537) and the Ural Division of the Russian Academy of Sciences (interdisciplinary project no. 74, programs “Quantum Macrophysics” and “Strongly Correlated Electrons in Semiconductors,Metals, Superconductors, and Magnetic Materials”). Z.P. and I.N. are grateful to the “Dynasty” Foundation, the International Center for Fundamental Physics (Moscow), and the Russian Science Support Foundation for support. I.N. is grateful to the Council on Grants from the President of the Russian Federation for support (grant no. MK-2118.2005.02)
Предметные рубрики: DENSITY
Аннотация: The band structure of the Nd2-xCexCuO4 HTSC is calculated using the LDA+GTB method, which combines the local density approximation (LDA) and the generalized tight-binding (GTB) method. Two mechanisms of the concentration dependence of the band structure (single-electron and many-electron mechanisms) are taken into account. It is demonstrated that the main contribution to the evolution of the band structure with doping comes from the many-electron mechanism.
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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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Вид документа : Статья из журнала
Шифр издания : Physics, Applied/C94
Автор(ы) : Korshunov M. M., Ovchinnikov S. G., Shneyder E. I., Gavrichkov V. A., Orlov Yu.S., Nekrasov I. A., Pchelkina Z. V.
Заглавие : Cuprates, manganites and cobaltites: Multielectron approach to the band structure
Место публикации : Mod. Phys. Lett. B: WORLD SCIENTIFIC PUBL CO PTE LTD, 2012. - Vol. 26, Is. 24. - Ст.1230016. - ISSN 0217-9849, DOI 10.1142/S0217984912300165
Примечания : Cited References: 93. - We are thankful to O. K. Andersen, V. I. Anisimov, A. F. Barabanov, K. I. Kikoin, N. M. Plakida, S. Sakai, A.-M.S. Tremblay, V. V. Val'kov, and R. O. Zaitsev for useful discussions. This work was supported by the Presisium of RAS program Quantum physics of condensed matter N 20.7, Grant "Leading scientific schools of Russia" (NSh 1044-2012.2), RFBR (Grant No. 09-02-00127), Integration Grant of SBRAS-UrBRAS N 44, Grant of President of Russia MK-1683.2010.2, FCP Scientific and Research-and-Educational Personnel of Innovative Russia for 2009-2013 (GK 16.740.12.0731 and GK 16.740.11.0740), and Siberian Federal University (Theme N F-11). M.M.K. and E.I.S. acknowledges support from The Dynasty Foundation and ICFPM.
Предметные рубрики: HIGH-TEMPERATURE SUPERCONDUCTORS
MEAN-FIELD THEORY
DENSITY-FUNCTIONAL FORMALISM
CORRELATED ELECTRON-SYSTEMS
TRANSITION-METAL COMPOUNDS
SPIN-STATE TRANSITION
T-J MODEL
MAGNETIC-PROPERTIES
COPPER OXIDES
LaCoO3
Ключевые слова (''Своб.индексиров.''): lda plus gtb method--strongly-correlated systems--band structure
Аннотация: High-T-c superconductors with CuO2 layers, manganites La1-xSrxMnO3 and cobaltites LaCoO3 present several mysteries in their physical properties. Most of them are believed to come from the strongly-correlated nature of these materials. From the theoretical viewpoint, there are many hidden rocks in making the consistent description of the band structure and low-energy physics starting from the Fermi-liquid approach. Here, we discuss the alternative method - multielectron approach to the electronic structure calculations for the Mott insulators - called LDA + GTB (local density approximation + generalized tight-binding) method. Its origin is a straightforward generalization of the Hubbard perturbation theory in the atomic limit and the multiband p - d Hamiltonian with the parameters calculated within LDA. We briefly discuss the method and focus on its applications to cuprates, manganites and cobaltites.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Korshunov M. M., Gavrichkov V. A., Ovchinnikov S. G., Nekrasov I. A., Kokorina E. E., Pchelkina Z. V.
Заглавие : Dominance of many-body effects over the one-electron mechanism for band structure doping dependence in Nd2-xCexCuO4: the LDA + GTB approach
Разночтения заглавия :авие SCOPUS: Dominance of many-body effects over the one-electron mechanism for band structure doping dependence in Nd2-xCexCuO4: The LDA+GTB approach
Место публикации : J. Phys.: Condens. Matter: IOP PUBLISHING LTD, 2007. - Vol. 19, Is. 48. - Ст.486203. - ISSN 0953-8984, DOI 10.1088/0953-8984/19/48/486203
Примечания : Cited References: 36
Предметные рубрики: NARROW ENERGY BANDS
HUBBARD-MODEL
SUPERCONDUCTORS
DENSITY
TEMPERATURE
ORBITALS
WAVE
Ключевые слова (''Своб.индексиров.''): antiferromagnetism--band structure--correlation methods--crystal structure--local density approximation--superconducting materials--electronic correlations--fermionic quasiparticles--neodymium compounds
Аннотация: In the present work we report band structure calculations for the high-temperature superconductor Nd2-xCexCuO4 in the regime of strong electronic correlations within an LDA + GTB method, which combines the local density approximation (LDA) and the generalized tight-binding method (GTB). The two mechanisms of band structure doping dependence were taken into account. Namely, the one-electron mechanism provided by the doping dependence of the crystal structure, and the many-body mechanism provided by the strong renormalization of the fermionic quasiparticles due to the large on-site Coulomb repulsion. We have shown that, in the antiferromagnetic and in the strongly correlated paramagnetic phases of the underdoped cuprates, the main contribution to the doping evolution of the band structure and Fermi surface comes from the many-body mechanism.
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11.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Makarov I. A., Gavrichkov V. A., Shneyder E. I., Nekrasov I. A., Slobodchikov A. A., Ovchinnikov S. G., Bianconi A.
Заглавие : Effect of CuO2 lattice strain on the electronic structure and properties of high-Tc cuprate family
Место публикации : J. Supercond. Novel Magn. - 2019. - Vol. 32, Is. 7. - P.1927-1935. - ISSN 15571939 (ISSN) , DOI 10.1007/s10948-018-4936-9
Примечания : Cited References: 51. - We thank the Presidium RAS program No.12 “Fundamental problems of high temperature superconductivity” for the financial support under the project 0356-2018-0063. The reported study was funded by the Russian Foundation for Basic Research, Government of Krasnoyarsk Territory and Krasnoyarsk Regional Fund of Science according to the research project:“Features of electron-phonon coupling in high-temperature superconductors with strong electronic correlations” No. 18-42-240017. This work was done under the State contract (FASO) No. 0389-2014-0001 and supported in part by RFBR grants No. 17-02-00015 and 18-02-00281.
Аннотация: Doping and strain dependences of the electronic structure of the CuO6-octahedra layer within LDA+GTB method in the frameworks of six-band p-d model are calculated. Band structure and Fermi surface of the quasiparticle excitations in the effective Hubbard model are characterized by inhomogeneous distribution of the k-dependent spectral weight. Doping results in reconstruction of the band structure, redistribution of the spectral weight over dispersion surface, and reconstruction of Fermi surface from small hole pockets in the underdoped region to large hole contour in the overdoped region through two quantum phase transitions (QPT). Strain increasing leads to displacement of the valence and conductivity bands, bandwidths decreasing, and shift of the concentrations corresponding to QPTs. Strain dependences of the antiferromagnetic exchange coupling and DOS at the Fermi level determining superconducting temperature Tc are obtained. Effective exchange coupling in the equation for Tc demonstrates monotonic strain dependence.
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12.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Sidorov K. A., Gavrichkov V. A., Nikolaev S. V., Pchelkina Z. V., Ovchinnikov S. G.
Заглавие : Effect of external pressure on the normal and superconducting properties of high-Tc cuprates
Место публикации : Phys. Status Solidi B. - 2016. - Vol. 253, Is. 3. - P.486-493. - ISSN 0370-1972, DOI 10.1002/pssb.201552465
Примечания : Cited References: 50. - We are thankful to Dr. M.M. Korshunov for useful discussions. This work was supported by RFBR Grants 13-02-01395, 14-02-00186, grant of Russian President NSh-2886.2014.2, and the Ministry of Education and Science of Russia (SibFU Government Contract for 2014-2016, No. 3085).
Предметные рубрики: HYDROSTATIC-PRESSURE
ELECTRONIC-STRUCTURE
EXCHANGE INTERACTION
HEISENBERG-MODEL
COPPER OXIDES
FERMI-SURFACE
SPIN-WAVE
Ключевые слова (''Своб.индексиров.''): cuprates--electronic structure--fermi surface--lifshitz transitions--strongly correlated electrons--superconducting properties
Аннотация: The pressure effects on the normal state electronic structure, the superexchange interaction, and the critical temperature of d-type superconductivity mediated by magnetic pairing have been studied within the multielectron hybrid scheme LDA+GTB that takes into account electron correlations in CuO2 planes. We have found the changes of the multiband p–d model parameters at 3% compression of different symmetry: (i) hydrostatic, (ii) along the c-axis, and (iii) in a–b plane. We have studied the changes of the Fermi surface under external pressure for different hole doping concentration x. In general, this effect is too small except two critical concentrations xc1≈0.15 and xc2=0.24 where the Lifshitz transitions occur with the change of the Fermi surface topology. In the vicinity of the critical concentration, we have found the giant change of the Fermi surface area up to 100% related to the pressure-induced Lifshitz transition. The effects of pressure on the antiferromagnetic coupling J and the mean-field value of Tc are obtained in a good agreement to experimental data.
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13.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Korshunov M. M., Gavrichkov V. A., Ovchinnikov S. G., Manske D., Eremin I.
Заглавие : Effective parameters of the band dispersion in n-type high-T-c superconductors
Разночтения заглавия :авие SCOPUS: Effective parameters of the band dispersion in n-type high-Tc superconductors
Место публикации : Physica C: ELSEVIER SCIENCE BV, 2004. - Vol. 402, Is. 4. - P365-370. - ISSN 0921-4534, DOI 10.1016/j.physc.2003.10.017
Примечания : Cited References: 32
Предметные рубрики: DOPED CUPRATE SUPERCONDUCTORS
TIGHT-BINDING METHOD
QUASI-PARTICLES
COPPER OXIDES
LA2-XSRXCUO4
SYMMETRY
MODEL
EVOLUTION
ORDER
Ключевые слова (''Своб.индексиров.''): high-t-c superconductivity--electronic correlations--electron-doped cuprates--electron-doped cuprates--electronic correlations--high-tc superconductivity--approximation theory--atomic physics--band structure--binding energy--charge transfer--correlation methods--doping (additives)--electronic structure--hamiltonians--mathematical models--mathematical operators--oxide superconductors--perturbation techniques--photoelectron spectroscopy--atomic orbitals--conduction band--electron doped cuprates--electron spins--valence band--high temperature superconductors
Аннотация: The electronic structure of electron-doped cuprates is discussed in the regions of small and optimal doping. For optimal doping we obtain the parameters from a simple tight-binding analysis by fitting ARPES data, and for small doping we study the band structure by the generalized tight-binding method that takes strong electronic correlations into account explicitly. This method has also reproduced well the ARPES data for small doping. The effective low-energy Hamiltonian is the t-t'-J model with hopping parameters t and t'. We compare both methods and find very good agreement for the value of t while t' is different because it is caused by the different contribution of the short-range spin correlations. (C) 2003 Elsevier B.V. All rights reserved.
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14.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Gavrichkov V. A., Korshunov M. M., Shneyder E. I.
Заглавие : Electron structure and electron-phonon interaction in the strongly correlated electron system of cuprates
Место публикации : Low Temp. Phys. - 2006. - Vol. 32, Is. 4-5. - P.483-488. - ISSN 1063-777X, DOI 10.1063/1.2199450; \b Физика низких температур
Примечания : Cited References: 37
Предметные рубрики: HIGH-TEMPERATURE SUPERCONDUCTORS
HIGH-TC SUPERCONDUCTIVITY
C SUPERCONDUCTORS
J MODEL
BAND
REPRESENTATION
REGIME
OXIDES
Аннотация: The generalized tight-binding method presents a practical realization of the scheme that describes quasiparticles in a strongly correlated electron system and consists of exact intra-cell diagonalization of the model Hamiltonian and perturbative treatment of the inter-cell hoppings. In the present paper this method and its ab initio modification are applied to undoped and weakly doped HTSC cuprates. Results are in very good agreement with the experimental ARPES data on various compounds. Starting with a multiband p-d model the realistic effective low-energy Hamiltonian of strongly correlated electrons interacting with spin fluctuations and phonons is derived both for hole- and electron-doped systems. Without electron-phonon interaction the pure magnetic mechanism of pairing does not provide the correct value of T, even for single-layer La2-xSrxCuO4 and Nd2-xCexCuO4. (c) 2006 American Institute of Physics.
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15.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gavrichkov V. A., Ovchinnikov S. G., Nekrasov I. A., Pchelkina Z. V.
Заглавие : Electronic Structure of p-Type La1-xMx2+MnO3 Manganites in the Ferromagnetic and Paramagnetic Phases in the LDA plus GTB Approach
Разночтения заглавия :авие SCOPUS: Electronic structure of p-Type La 1-x M x 2+ MnO 3 manganites in the ferromagnetic and paramagnetic phases in the LDA + GTB approach
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2011. - Vol. 112, Is. 5. - P860-876. - ISSN 1063-7761, DOI 10.1134/S1063776111030101
Примечания : Cited References: 47. - This study was supported financially by integration project no. 40 of the Ural and Siberian Branches of the Russian Academy of Sciences, the program "Strong Electron Correlations" of the Russian Academy of Sciences, and the Russian Foundation for Basic Research (project no. 10-02-00251-a).
Предметные рубрики: DOUBLE-EXCHANGE
COLOSSAL MAGNETORESISTANCE
THIN-FILMS
PHYSICS
LA1-XSRXMNO3
RESISTIVITY
SEPARATION
TRANSPORT
MODEL
Ключевые слова (''Своб.индексиров.''): complex structure--cubic materials--ferromagnetic phase--half metals--jahn teller effect--metal properties--metal types--orbitals--p-type--paramagnetic phase--paramagnetic phasis--quasi particles--spectral intensity--spin projections--strong electron correlations--barium--density functional theory--electron correlations--electron density measurement--electronic properties--electronic structure--fermi level--ferromagnetic materials--ferromagnetism--manganese oxide--manganites--paramagnetic materials--paramagnetism--valence bands--lanthanum
Аннотация: The band structure, spectral intensity, and position of the Fermi level in doped p-type La1-xMx2+ MnO3 manganites (M = Sr, Ca, Ba) is analyzed using the LDA + GBT method for calculating the electronic structure of systems with strong electron correlations, taking into account antiferro-orbital ordering and using the Kugel-Khomskii ideas and real spin S = 2. The results of the ferromagnetic phase reproduce the state of a spin half-metal with 100% spin polarization at T = 0, when the spectrum is of the metal type for a quasiparticle with one spin projection and of the dielectric type for the other. It is found that the valence band becomes approximately three times narrower upon a transition to the paramagnetic phase. For the paramagnetic phase, metal properties are observed because the Fermi level is located in the valence band for any nonzero x. The dielectrization effect at the Curie temperature is possible and must be accompanied by filling of d(x) orbitals upon doping. The effect itself is associated with strong electron correlations, and a complex structure of the top of the valence band is due to the Jahn-Teller effect in cubic materials. DOI: 10.1134/S1063776111030101
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16.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gavrichkov V. A., Ovchinnikov S. G., Borisov A. A., Goryachev E. G.
Заглавие : Evolution of the band structure of quasiparticles with doping in copper oxides on the basis of a generalized tight-binding method
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 2000. - Vol. 91, Is. 2. - P369-383. - ISSN 1063-7761, DOI 10.1134/1.1311997
Примечания : Cited References: 45
Предметные рубрики: T-J MODEL
CUPRATE SUPERCONDUCTORS
ELECTRONIC-STRUCTURE
EXCITATIONS
DEPENDENCE
TEMPERATURE
DERIVATION
SR2CUO2CL2
SPECTRUM
DENSITY
Аннотация: Two methods for stabilizing the two-hole B-3(1g) state as the ground state instead of the Zhang-Rice singlet are determined on the basis of an orthogonal cellular basis for a realistic multiband pd model of a CuO2 layer and the dispersion relations for the valence band top in undoped and doped cases are calculated. In the undoped case, aside from the valence band, qualitatively corresponding to the experimental ARPES data for Sr2CuO2Cl2 and the results obtained on the basis of the t-t'-J model, the calculations give a zero-dispersion virtual level at the valence band top itself. Because of the zero amplitude of transitions forming the virtual level the response corresponding to it is absent in the spectral density function. In consequence, the experimental ARPES data do not reproduce its presence in this antiferromagnetic undoped dielectric. A calculation of the doped case showed that the virtual level transforms into an impurity-type band and acquires dispersion on account of the nonzero occupation number of the two-hole states and therefore should be detected in ARPES experiments as a high-energy peak in the spectral density. The computed dispersion dependence for the valence band top is identical to the dispersion obtained by the Monte Carlo method, and the ARPES data for optimally doped Bi2Sr2CaCu2O8 + delta samples. The data obtained also make it possible to explain the presence of an energy pseudogap at the symmetric X point of the Brillouin band of HTSC compounds. (C) 2000 MAIK "Nauka/Interperiodica".
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17.

Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Gavrichkov V. A., Polukeev S. I., Malakhovskii A. V.
Заглавие : Exchange interaction between excited states of magnetic ions
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.H.I1. - P.36-37. - ISBN 978-5-9500855-7-4 (Шифр В33/E12-125657784)
Примечания : Cited References: 8. - Support by RSF grant 18-12-00022 is acknowledged
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18.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Gavrichkov V. A., Polukeev S. I., Malakhovskii A. V.
Заглавие : Exchange Interaction between the Excited States of Magnetic Ions
Место публикации : Phys. Metals Metallogr. - 2019. - Vol. 120, Is. 13. - P.91-94. - ISSN 0031-918X (ISSN), DOI 10.1134/S0031918X19130210. - ISSN 1555-6190 (eISSN)
Примечания : Cited References: 11. - This work was supported by the Russian Science Foundation, project no. 18-12-00022.
Аннотация: Within the framework of the LDA + GTB multi-electron approach to the electron structure of Mott–Hubbard insulators a scheme is developed for constructing the effective low-energy Hamiltonian that includes not only the ground state of the magnetic cation, but also the excited terms. The mathematical apparatus of the theory are Hubbard operators built on the many-electron states of the cation in the dn configuration. The occupation of the excited term under optical pumping can change the sign of the exchange interaction of the excited cation with the neighboring cation in the ground state. Another variant of the occupation of the excited states is connected with a spin crossover when the excited and the ground terms change over, for example, at high pressure. Examples are given for such crystals as FeBO3, Nd0.5Gd0.5Fe3(BO3)4 and NiO.
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19.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Orlov Yu. S., Nikolaev S. V., Gavrichkov V. A., Ovchinnikov S. G.
Заглавие : Exchange interaction between the high spin Co3+ states in LaCoO3
Место публикации : Comput. Mater. Sci. - 2022. - Vol. 204. - Ст.111134. - ISSN 09270256 (ISSN), DOI 10.1016/j.commatsci.2021.111134
Примечания : Cited References: 59. - We are thankful to the Russian Science Foundation, Russia for the financial support under the project 18-12-00022
Аннотация: The formation of the exchange interaction between HS Co3+ ions, which are excited in LaCoO3, is studied within the multielectron approach. Two main contributions appear to be antiferromagnetic (AFM) and ferromagnetic (FM). When the ground state is LS, the total interaction is AFM. The crossover to the HS state may result in the FM ordering. The mean-field magnetic phase diagrams on the plane spin gap-temperature have been calculated without and with spin-orbital interaction in the HS term. Without spin-orbital interaction the reentrant magnetic order is possible. The spin-orbital coupling removes the reentrant phase transition and stabilizes the LS state. For known from experimental data values of the spin gap and exchange interaction, the ideal stoichiometric LaCoO3 is very close to the LS–HS crossover and magnetic ordering border. The violations of local coordination and symmetry of the Co3+-oxygen complexes that take place in the intergrain boundaries, at the surface of single crystals, and in the thin films on the strained substrate, may result in the formation of the HS state and FM order for such materials.
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20.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Orlov Yu. S., Nikolaev S. V., Dudnikov V. A., Gavrichkov V. A., Ovchinnikov S. G.
Заглавие : Features of spin crossovers in magnetic materials
Колич.характеристики :26 с
Место публикации : Phys. Usp. - 2023. - Vol. 66, Is. 7. - P.647-672. - ISSN 10637869 (ISSN), DOI 10.3367/UFNe.2022.05.039195. - ISSN 14684780 (eISSN)
Примечания : Cited References: 237. - The authors thank the Russian Science Foundation for financial support in the framework of project no. 18-12-00022
Аннотация: We present experimental and theoetical results of spin crossover studies in magnetically ordered materials. The effect of spin crossovers on the electronic structure of transition metal oxides and on the Bose condensation of spin excitons in the vicinity of the spin crossover is considered. A new method for calculating the interatomic superexchange interaction in transition metal oxides is discussed that allows considering selective contributions of excited magnetic cation terms. Changes in the exchange interaction sign are predicted for spin crossovers for d5—d7 ions. In the RCoO3 family of rare-earth cobaltites, the ground state is nonmagnetic, but, as the temperature increases, thermal excitations of high-spin states give rise to a number of experimentally detectable features. In defective RCoO3 samples, stabilization of the high-spin term and ferromagnetic ordering are possible. Dynamical crossovers under external pumping and the dynamics of multiplicity, magnetization, and local lattice distortions are discussed. Geophysical implications of spin crossovers are considered, and metallic properties of Earth's mantle at a depth of 1400—1800 km are predicted.
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