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Общее количество найденных документов : 154
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1.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Sidorov K. A., Ovchinnikov S. G., Tikhonov N. V.
Заглавие : Simple method for exact calculation of thermodynamic properties of the 1D Hubbard model with infinite repulsion
Место публикации : J. Experim. Theor. Phys. - 2013. - Vol. 116, Is. 2. - P.330-337. - DOI 10.1134/S1063776113020167
Аннотация: It is shown that the canonical partition function in the 1D Hubbard model with U = ∞ in the near-est neighbor approximation is determined by the product of canonical partition functions of spinons andholons. In this approximation, the concentration and temperature dependences of the free and internal ener gies, as well as of the chemical potential, entropy, and heat capacity, are calculated for electron concentrations of 0 ≤ n[[d]]e[[/d]] ˂ 1
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2.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Korshunov M. M., Makarov I. A., Shneyder E. I.
Заглавие : Quantum phase transitions and superconductivity in single- and two-layer cuprates in the multiband theory of Hubbard fermions
Место публикации : J. Supercond. Nov. Magn. - 2013. - Vol. 26, Is. 8. - P.2607-2609. - ISSN 1557-1939, DOI 10.1007/s10948-013-2144-1. - ISSN 1557-1947
Аннотация: We consider the doping dependence of the normal and superconducting properties of La2Sr2−x CuO2 and YBa2Cu3O7 in the low energy effective model based on the ab initio LDA+GTB calculations. With doping we have found a concentration region with electronic instability of the uniform state. We have shown that two quantum phase transitions (QPT) of the Lifshitz type correspond well to the experimental phase diagram. For superconducting state we have considered both magnetic and phonon mechanisms of pairing.
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3.

Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Makarov I. A., Shneyder E. I., Togushova Yu. N., Korshunov M. M., Gavrichkov V. A.
Заглавие : Magnetic mechanisms of pairing in strongly correlated electron system of copper oxides
Место публикации : Recent advances in superconductivity research. - New York: Nova Science Publishers, 2013. - Chapter 6. - P.93-143. - ISBN 978-1-62618-406-0
Ключевые слова (''Своб.индексиров.''): strong electronic correlations--magnetic mechanism of pairing--quantum phase transitions--electronic structure--hubbard operators--cuprates
Аннотация: The multielectron LDA+GTB approach has been developed to calculate electronic structure of strongly correlated cuprates. At low energies the effective Hamiltonian of the t- t’- t”- t﬩-J*-J﬩ -model has been derived with parameters coming from the ab initio calculation for LSCO. The electronic structure of LSCO has been calculated self-consistently with the short-range antiferromagnetic order for various doping level. Two Lifshitz-type quantum phase transitions with Fermi surface topology changes have been found at dopings x(c1) = 0.15 and x(c2) = 0.24. Its effect on normal and superconducting properties has been calculated. The interatomic ex­ change parameter and its pressure dependence has been calculated within LDA+GTB scheme. The magnetic mechanisms of d-wave pairing induced by static and dynamical spin correlations are discussed. Simultaneous treatment of magnetic and phonon pairing results in the conclusion that both contributions are of the same order. For two layer cuprates like YBCO the interlayer hopping and exchange effects on the electronic structure and doping dependence of Tc is discussed as well as the Coulomb interaction induced mechanism of pairing.
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4.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kagan M. Y., Efremov D. V., Mar'enko M. S., Val'kov V. V.
Заглавие : Superconductivity in repulsive fermi-systems at low density
Коллективы : RFBR [11-02-00741]
Место публикации : J. Supercond. Nov. Magn.: SPRINGER, 2013. - Vol. 26, Is. 9. - P.2809-2815. - ISSN 1557-1939, DOI 10.1007/s10948-013-2262-9
Примечания : Cited References: 57. - The authors acknowledge helpful discussions with A. V. Chubukov, A. S. Alexandrov, V. V. Kabanov, K. I. Kugel, Yu. V. Kopaev, N.M. Plakida, N.V. Prokof'ev, M. M. Korovushkin, M. A. Mitskan. M. Yu. K. work was supported by RFBR grant No. 11-02-00741.
Предметные рубрики: T-J MODEL
SUPERFLUID TRANSITION-TEMPERATURE
FRACTIONAL-STATISTICS
PHASE-SEPARATION
HUBBARD-MODEL
GAS
ENHANCEMENT
MECHANISM
EXCHANGE
PARTICLES
Ключевые слова (''Своб.индексиров.''): anomalous superconductivity--p-wave and d-wave pairings--kohn-luttinger mechanism--shubin-vonsovsky--hubbard and t-j models
Аннотация: In the large variety of models such as 3D and 2D Fermi-gas model with hard-core repulsion, 3D and 2D Hubbard model, and the Shubin-Vonsovsky model, we demonstrate the possibility of triplet p-wave pairing at low electron density. We show that the critical temperature of the p-wave pairing can be strongly increased in a spin-polarized case or in a two-band situation already at low density and reach experimentally feasible values of (1-5) K. We also discuss briefly d-wave pairing and high-T-C superconductivity with T-C similar to 100 K, which arises in the 2D t-J model in the range of parameters realistic for cuprates.
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5.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kagan M.Yu., Efremov D. V., Mar'Enko M. S., Val'kov V. V.
Заглавие : Kohn-Luttinger effect and anomalous pairing in repulsive Fermi-systems at low density : Review Article
Место публикации : Физ. низких температур: Физико-технический институт низких температур им. Б.И. Веркина НАН Украины, 2012. - Т. 38, Вып. 9. - С.1102-1108. - ISSN 0132-6414
Примечания : Библиогр.: 59 назв. - We acknowledge helpful discussions with A. V. Chubukov, A. S. Alexandrov, V. V. Kabanov, K. I. Kugel, Yu. V. Kopaev, N. M. Plakida, and N. V. Prokof'ev. M. Yu. K's work was supported by RFBR Grant No 11-02-00741-a.
Ключевые слова (''Своб.индексиров.''): 3d and 2d hubbard model--fermi-gas model--superconductivity
Аннотация: In the large variety of models such as 3D and 2D Fermi-gas model with hard-core repulsion, 3D and 2D Hubbard model, and Shubin-Vonsovsky model we demonstrate the possibility of triplet p-wave pairing at low electron density. We show that the critical temperature of the p-wave pairing can be strongly increased in a spinpolarized case or in a two-band situation already at low density and reach experimentally observable values of (1-5) K. We also discuss briefly d-wave pairing and high-T c superconductivity with T c ∼ 100 K which arises in the extended Hubbard model and in the generalized t-J model close to half-filling.
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6.

Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Korshunov M. M., Nikolaev S. N., Shneyder E. I.
Заглавие : Quantum phase transitions and superconductivity in single- and two-layer cuprates in the multiband theory of Hubbard fermions
Коллективы : Ettore Majorana Foundation, Centre for Scientific Culture, Rome International Center for Materials Science, International School of Solid State Physics, "Phase separation and Superstripes in High Temperature Superconductors and Related Materials", Int. Conf. (55; 2012 ; July ; 11-17; Erice (Sicily), Italy)
Место публикации : International conferences «Phase separation and Superstripes in High Temperature Superconductors and Related Materials (Superstripes-2012)». - 2012. - P.128
Аннотация: We consider the doping dependence of the normal and superconducting properties of LaSrCuO and YBaCuO in the low energy effective model based on the ab initio LDA+GTB calculations. With doping we have found a concentration region with electronic instability of the uniform state. We have shown that two quantum phase transitions (QPT) of the Lifshitz type correspond well to the experimental phase diagram. For superconducting state we have considered both magnetic and phonon mechanisms of pairing.
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7.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kagan M. Y., Val'kov V. V.
Заглавие : Anomalous resistivity and the electron-polaron effect in the two-band hubbard model with one narrow band
Место публикации : J. Supercond. Nov. Magn.: SPRINGER, 2012. - Vol. 25, Is. 5. - P.1379-1382. - ISSN 1557-1939, DOI 10.1007/s10948-012-1523-3
Примечания : Cited References: 28. - We are grateful to P. Fulde, Yu. Kagan, K. I. Kugel, N.V. Prokof'ev, P. Nozieres, and C. M. Varma for the numerous stimulating discussions. We acknowledge financial support of the RFBR Grant No. 11-02-00741.
Предметные рубрики: FERMI GAS
SUPERCONDUCTIVITY
SUPERFLUIDITY
TEMPERATURE
REPULSION
SYSTEMS
Ключевые слова (''Своб.индексиров.''): electron-polaron effect--two-band hubbard model--marginality--anomalous resistivity
Аннотация: We search for anomalous normal and superconductive behavior in the two-band Hubbard model with one narrow band. We analyze the influence of the electron–polaron effect and the Altshuler–Aronov effect on effective mass enhancement and scattering times of heavy and light components in the clean case. We find anomalous behavior of resistivity at high temperatures TW∗hT W_{h}. *} both in 3D and 2D situations. The SC instability in the model is governed by an enhanced Kohn–Luttinger effect for p-wave pairing of heavy electrons via polarization of light electrons.
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8.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kagan M. Y., Efremov D. V., Mar'enko M. S., Val'kov V. V.
Заглавие : Kohn-Luttinger effect and anomalous pairing in repulsive Fermi-systems at low density : Review Article
Место публикации : Low Temp. Phys.: American Institute of Physics, 2012. - Vol. 38, Is. 9. - P.874-879. - ISSN 1063-777X, DOI 10.1063/1.4752091
Примечания : Cited References: 59. - We acknowledge helpful discussions with A. V. Chubukov, A. S. Alexandrov, V. V. Kabanov, K. I. Kugel, Yu. V. Kopaev, N. M. Plakida, and N. V. Prokof'ev. M. Yu. K's work was supported by RFBR Grant No 11-02-00741-a.
Предметные рубрики: T-J MODEL
SUPERFLUID TRANSITION-TEMPERATURE
2-BAND HUBBARD-MODEL
LOW ELECTRON-DENSITY
FRACTIONAL-STATISTICS
PHASE-SEPARATION
SUPERCONDUCTIVITY
GAS
ENHANCEMENT
MECHANISM
Ключевые слова (''Своб.индексиров.''): d-wave superconductivity--electron density--electron spin polarisation--high-temperature superconductors--hubbard model--superconducting transition temperature--t-j model--two-dimensional electron gas
Аннотация: We demonstrate the possibility of triplet p-wave pairing at low electron density a large number of models such as 3D and 2D Fermi-gas models with hard-core repulsion, 3D and 2D Hubbard models, and the Shubin-Vonsovsky model. The critical temperature for p-wave pairing can be considerably higher in the spin-polarized case or even in a two-band situation at low density and can reach experimentally observable values of 1–5 K. We also discuss briefly the d-wave pairing and high-Tc superconductivity with Tc ∼ 100 K which arise in the extended Hubbard model and in the generalized t-Jmodel when close to half-filling.
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9.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Lyubutin I. S., Ovchinnikov S. G.
Заглавие : Spin crossovers in Mott-Hubbard insulators at high pressures
Коллективы : Moscow International Symposium on Magnetism
Место публикации : J. Magn. Magn. Mater.: Elsevier Science BV, 2012. - Vol. 324, Is. 21. - P.3538-3541. - ISSN 0304-8853, DOI 10.1016/j.jmmm.2012.02.084
Примечания : Cited References: 16. - We acknowledge the help and discussions with Drs. A.G. Gavriliuk, V.V. Struzkin and J.F. Lin. Supports by RFBR (Grants # 09-02-00171, 10-02-00251, # 11-02-00636, # 11-02-00291, # 11-02-12089) and by the RAS Program "Strongly correlated electronic systems" are acknowledged.
Предметные рубрики: ELECTRONIC-TRANSITION
MAGNETIC COLLAPSE
PHASE-TRANSFORMATIONS
BIFEO3 CRYSTAL
METAL-OXIDES
METALLIZATION
Ключевые слова (''Своб.индексиров.''): electronic structure--spin crossover--high pressure--magnetic transition
Аннотация: The high-pressure induced phase transitions initiated by electronic transition in 3d ions from the high-spin (HS) to the low-spin (LS) state (HS-LS spin-crossover) are considered. Behavior of the system with d(6) electronic configuration is investigated in the ground state of zero temperature and critical pressure P-c. Magnetic properties of the Mott-Hubbard insulator (Mg1-xFex)O are studied in the vicinity of the quantum critical point (T=0, P-c). At the critical pressure of spin crossover P-c, the spin gap energy epsilon(S) between HS and LS states is zero. The quantum spins fluctuations HS double left right arrow LS do not require any energy, and the antiferromagnetism is destroyed in the quantum critical point by the first order transition. (C) 2012 Published by Elsevier B.V.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Makarov I. A., Ovchinnikov S. G., Shneider E. I.
Заглавие : Dependence of the critical temperature of high-temperature cuprate superconductors on hoppings and spin correlations between CuO2 planes
Место публикации : J. Exp. Theor. Phys.: MAIK Nauka-Interperiodica / Springer, 2012. - Vol. 114, Is. 2. - P.329-342. - ISSN 1063-7761, DOI 10.1134/S1063776112020264
Примечания : Cited References: 73. - This study was supported in part by the Presidium of the Russian Academy of Sciences (program "Quantum Physics of Condensed Media," project no. 18.7), jointly by the Siberian and Ural branches of the Russian Academy of Sciences (integration projects project no. 40), the Russian Foundation for Basic Research (project no. 09-02-00127), the Presidential Program in Support of Young Scientists in Russia (project no. MK-1683.2010.2), and the federal target program "Specialists" (project no. P891). One of the authors (E.I.Sh.) gratefully acknowledges support from the nonprofit Dynasty foundation.
Предметные рубрики: T-J MODEL
BAND HUBBARD-MODEL
SINGLE-CRYSTALS
TRANSITION-TEMPERATURE
FERMI-SURFACE
DOPING DEPENDENCE
THERMAL-EXPANSION
COPPER OXIDES
ANISOTROPY
LA2-XSRXCUO4
Аннотация: The influence of interlayer hoppings on the superconducting transition temperature (T c) in bilayer cuprates has been studied. The parameter of hopping between layers is expressed as t ⊥(k) = t ⊥(cos(k x ) − cos(k y ))2 and treated as a small perturbation for the states of two CuO2 planes described by the t-t′-t″-J* model. In the generalized mean field approximation for dx2−y2{d_{{x. } - {y. }}} symmetry of the superconducting gap, neither the interlayer hopping or exchange interaction, nor the pair hopping between CuO2 layers provides an additional mechanism of Cooper pair formation or an increase in T c. In the concentration dependence of T c, the bilayer splitting of the upper Hubbard band of quasi-holes is manifested as two peaks with temperatures slightly lower than the maximum T c for a single-layer cuprate. Interlayer antiferromagnetic spin correlations suppress bilayer splitting.
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