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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Prodaivoda G. T., Aleksandrov K. S., Vyzhva S. A., Nazarenko L. V.
Заглавие : Computation of effective elastic constants in anisotropic microseamy rocks
Место публикации : Geol. Geofiz. - 2000. - Vol. 41, Is. 3. - P.436-449. - ISSN 0016-7886
Примечания : Cited References: 25
Предметные рубрики: WAVE-PROPAGATION
SYMMETRY
Ключевые слова (''Своб.индексиров.''): anisotropy--modeling--orientation of microcracks--elastic waves
Аннотация: A generalized method of conditional moments for computation of effective elastic constants of anisotropic rocks with spatially oriented microcracks is considered. The method involves an additional operation of averaging of known solution data for a modeled rock of orthorhombic structure with ellipsoidal microcracks whose semiaxes are oriented along the coordinate axes. The averaging is performed using the distribution function of rock microcrack orientations, which is expanded into a series in terms of generalized spherical functions. The expansion coefficients are determined by an experiment. In calculating the effective elastic constants of anisotropic rocks, there are no constraints on the concentration of microcracks. We have studied the parameters of azimuthal anisotropy of elastic-wave velocities in modeled amphibolites with ellipsoidal hornblende grains oriented along the coordinate axes and with three-planar and spatially oriented systems of microcracks. The obtained results agree with experimental data of ultrasonic determinations of elastic constants for amphibolite samples.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gavrichkov V. A., Korshunov M. M., Ovchinnikov S. G.
Заглавие : Doping dependent electronic structure of cuprates and the effective low energy Hamiltonian for the magnetic pairing
Коллективы : International Conference on New Theories, Discoveries and Applications of Superconductors and Related Materials
Место публикации : Int. J. Mod. Phys. B/ International Conference on New Theories, Discoveries and Applications of Superconductors and Related Materials (5 ; 2004 ; June ; 11-16 ; Chongqing, China). - 2005. - Vol. 19, Is. 1-3. - P.247-249. - ISSN 0217-9792, DOI 10.1142/S0217979205028335
Примечания : Cited References: 14
Предметные рубрики: COPPER OXIDES
SYMMETRY
MODEL
Ключевые слова (''Своб.индексиров.''): electronic structure--strong electron correlations--magnetic mechanism of pairing--electronic structure--magnetic mechanism of pairing--strong electron correlations--copper derivative--calculation--chemical reaction--chemical structure--conference paper--correlation analysis--electron--electronics--energy--hybridization--intermethod comparison--magnetism--mathematical analysis--mathematical model
Аннотация: The properties of the normal and superconducting phases of p- and n-type cuprates are investigated in the appropriate low-energy models in the approximation beyond Hubbard I considering spin fluctuations. Calculated chemical potential dependence on doping, Fermi surface and T,(x) phase diagram for n-type cuprates are in remarkably good agreement with the experimental ones. Comparison of the singlet-triplet t-J model with simple t-J model shows that the spin-exciton mechanism originated from singlet-triplet hybridization leads to small contribution to the T-c(x) - optimal doping value becomes slightly lower and the maximum value of T-c become slightly higher.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Korshunov M. M., Ovchinnikov S. G., Sherman A. V.
Заглавие : Effective hamiltonian and properties of the normal and superconducting phases of n-type cuprates
Разночтения заглавия :авие SCOPUS: Effective Hamiltonian and properties of the normal and superconducting phases of n-type cuprates
Место публикации : JETP Letters. - 2004. - Vol. 80, Is. 1. - P.39-43. - ISSN 0021-3640, DOI 10.1134/1.1800212
Примечания : Cited References: 32
Предметные рубрики: T-J MODEL
ORDER-PARAMETER
QUASI-PARTICLES
COPPER OXIDES
FERMI-SURFACE
ELECTRON
SYMMETRY
RANGE
ND1.85CE0.15CUO4
TRANSITIONS
Аннотация: An effective low-energy Hamiltonian is derived from a microscopic multiband p-d model in the regime of strong electron correlations. The parameters of the p-d model are determined by comparison with the ARPES data for undoped Nd2CuO4. The Hamiltonian is the t-J* model in which hopping and exchange slowly decay with distance and are taken into account up to the fifth coordination sphere. The quasiparticle band structure is calculated as a function of the doping concentration with regard to short-range magnetic order, and the superconductivity theory with the spin-fluctuation pairing mechanism is constructed. Assuming that the parameters of the model do not depend on the doping level, we obtained quantitative agreement with the properties observed experimentally for the normal and superconducting phases without introducing fitting parameters. (C) 2004 MAIK "Nauka / Interperiodica".
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Korshunov M. M., Ovchinnikov S. G., Sherman A. V.
Заглавие : Effective Hamiltonian and the properties of normal and superconductive phases of n-type cuprates
Место публикации : Physica B: ELSEVIER SCIENCE BV, 2005. - Vol. 359: International Conference on Strongly Correlated Electron Systems (SCES 04) (JUL 26-30, 2004, Karlsruhe, GERMANY). - P521-523. - ISSN 0921-4526, DOI 10.1016/j.physb.2005.01.134
Примечания : Cited References: 13
Предметные рубрики: MODEL
SYMMETRY
Ключевые слова (''Своб.индексиров.''): strong electron correlations--superconductivity--multiband p-d model--n-type cuprates--multiband p-d model--n-type cuprates--strong electron correlations--superconductivity--antiferromagnetism--correlation theory--fermi surface--hamiltonians--mathematical models--microscopic examination--oxide superconductors--phase diagrams--semiconductor doping--generalized tight-binding (gtb)--multiband p-d models--n-type cuprates--single electron correlations--superconductivity
Аннотация: In the framework of the effective low-energy model for high-T-c, cuprates with account for three-center interaction terms and spin fluctuations the properties of normal and superconducting phases of n-type cuprates are investigated. Microscopic model parameters were obtained from ARPES data in undoped compounds. Obtained evolution of the chemical potential with doping, Fermi surface at optimal doping, and T-c(x) phase diagram are in remarkably good agreement with the experiment. (c) 2005 Elsevier B.V. All rights reserved.
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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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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Pankrats A. I., Sablina K. A., Eremin M., Balaev A. D., Kolkov M., Tugarinov V. I., Bovina A. F.
Заглавие : Ferromagnetism and strong magnetic anisotropy of the PbMnBO4 orthoborate single crystals
Место публикации : J. Magn. Magn. Mater.: Elsevier, 2016. - Vol. 414. - P.82-89. - ISSN 0304-8853, DOI 10.1016/j.jmmm.2016.04.042
Примечания : Cited References: 20. - We acknowledge the assistance of A. Dubrovsky in magnetic measurements.This work was supported by the Russian Foundation for Basic Research, Projects nos. 13-02-00897 and 16-02-00563. MVE thanks for support the Russian Government Program of Competitive Growth of the Kazan Federal University, decision no. 930_p, May 22, 2015.
Предметные рубрики: PbMBO4 M
Resonance
Symmetry
Mn
Fe
Cr
Ключевые слова (''Своб.индексиров.''): strong ferromagnetic anisotropy--ferromagnetic resonance--exchange interactions
Аннотация: The PbMnBO4 orthoborate single crystals were first grown and their magnetic properties and ferromagnetic resonance were studied. It was found that the ferromagnetic state below the Curie temperature TC=31 K is characterized by the strong magnetic anisotropy. The significant effective anisotropy fields of PbMnBO4 determine the energy gap in the FMR spectrum, which is extraordinary large for ferromagnets (112 GHz at T=4.2 K). It was shown that the static Jahn-Teller effect characteristic of the Mn3+ ion leads to both the ferromagnetic ordering and the strong magnetic anisotropy in the crystal. In the strong external magnetic field the induced ferromagnetic ordering is retained in the crystal above the Curie temperature up to the temperatures multiply higher than TC. A weak anomaly of the dielectric permittivity was observed in PbMnBO4 at the Curie temperature at which the long-range ferromagnetic order is established. © 2016 Elsevier B.V. All rights reserved.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Shneyder E. I., Ovchinnikov S. G.
Заглавие : Isotope effect in the model of strongly correlated electrons with the magnetic and phonon superconducting pairing mechanisms
Коллективы : Presidium of the Russian Academy of Sciences [40]; Russian Academy of Sciences; Russian Foundation for Basic Research [09-02-00127]
Место публикации : J. Exp. Theor. Phys. - 2009. - Vol. 109, Is. 6. - P.1017-1021. - ISSN 1063-7761, DOI 10.1134/S1063776109120139
Примечания : Cited References: 42. - This study was financed under programs 5.7 and "Quantum Physics of Condensed Matter" of the Presidium of the Russian Academy of Sciences, integration project no. 40 of the Siberian Branch and Ural Division of the Russian Academy of Sciences, and the Russian Foundation for Basic Research (project no. 09-02-00127).
Предметные рубрики: CUPRATE SUPERCONDUCTORS
PHASE-TRANSITIONS
3-CENTER INTERACTIONS
HUBBARD-MODEL
TEMPERATURE
LA2-XSRXCUO4
SYMMETRY
EXCHANGE
COPPER
BI2SR2CACU2O8+DELTA
Ключевые слова (''Своб.индексиров.''): ab initio calculations--calculated values--cooper pairing--isotope effect--magnetic mechanisms--order of magnitude--pairing mechanism--phonon mechanism--strongly correlated electrons--superconducting pairing mechanism--superconducting state--type theory--carrier mobility--electron-phonon interactions--isotopes--superconductivity--superconducting magnets
Аннотация: Peculiarities of the temperature isotope effect in a BCS-type theory describing the exchange and phonon mechanisms of Cooper pairing in a system of strongly correlated electrons are considered. The electron-phonon interaction constant is determined from the fitting of the calculated value of the isotope-effect index to the observed value with the parameters of La(2 - x) Sr (x) CuO(4) obtained from ab initio calculations. The value of this constant indicates that the contribution from the traditional pairing mechanism to the superconducting state is of the same order of magnitude as the contribution from the magnetic mechanism.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Flerov I. N., Burriel R., Gorev M. V., Isla P., Voronov V. N.
Заглавие : Low-temperature specific heat of the Rb2KScF6 elpasolite
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2003. - Vol. 45, Is. 1. - P167-170. - ISSN 1063-7834, DOI 10.1134/1.1537430
Примечания : Cited References: 9
Предметные рубрики: PHASE-TRANSITIONS
CRYOLITE (NH4)(3)SCF6
DISTORTED PHASES
SYMMETRY
Аннотация: The specific heat of single-crystal Rb2KScF6 is measured using ac calorimetry in the range 4-280 K. The results are discussed in the context of a group-theoretical analysis of possible distortions of the elpasolite structure and of experimental data obtained earlier with an adiabatic calorimeter in a narrower temperature region. (C) 2003 MAIK "Nauka/Interperiodica".
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Komogortsev S. V., Iskhakov R. S.
Заглавие : Magnetization curve and magnetic correlations in a nanochain of ferromagnetic grains with random anisotropy
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2005. - Vol. 47, Is. 3. - P495-501. - ISSN 1063-7834, DOI 10.1134/1.1884711
Примечания : Cited References: 31
Предметные рубрики: NANOCRYSTALLINE FERROMAGNETS
AMORPHOUS FERROMAGNETS
FIELD
MODEL
MICROSTRUCTURE
SIMULATIONS
DEPENDENCE
SYMMETRY
SYSTEM
MEDIA
Аннотация: The magnetization curve and magnetization correlation function are calculated for a ferromagnetic chain of single-domain nanoparticles with a randomly oriented anisotropy axis for different ratios between the exchange correlation and anisotropy energies. It is shown that the coercive force decreases as the exchange correlations increase. For strong exchange correlations, the magnetization curve is described by the following three successive magnetization processes as the applied field is increased: (i) nonuniform rotation of the magnetization of stochastic domains, (ii) collapse of the magnetic solitons, and (iii) nonuniform rotation of exchange-correlated magnetization vectors of the nanoparticles. For high fields, the calculated correlation function of the transverse magnetization components coincides with that predicted from linear theory. At low and zero fields, the main parameters of the correlation function (the variance and correlation radius) tend to certain finite values rather than diverge (as is the case in linear theory). The irreversible variation in the magnetization at low fields (the hysteresis loop) and the hysteresis of the main parameters of the correlation function are calculated. (c) 2005 Pleiades Publishing, Inc.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Mel'nikova S. V., Laptash N. M., Zhogal' A. L.
Заглавие : Phase transitions in the oxyfluoride (NH4)(3)NbOF6
Разночтения заглавия :авие SCOPUS: Phase transitions in the oxyfluoride (NH4)3NbOF 6
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2007. - Vol. 49, Is. 5. - P958-962. - ISSN 1063-7834, DOI 10.1134/S1063783407050253
Примечания : Cited References: 11
Предметные рубрики: RAY-DIFFRACTION INVESTIGATIONS
DISTORTED PHASES
SYMMETRY
DISORDER
CRYSTAL
Аннотация: (NH4)(3)NbOF6 single crystals were grown, polarization-optical studies were performed, and birefringence was measured over the temperature range 90-500 K. A sequence of first-order structural phase transitions was found at temperatures T (1 down arrow) = 259.7 K and T (2 down arrow) = 257.7 K with temperature hysteresis delta T-1 = 0.9 K and delta T-2 = 1.9 K. The transitions are accompanied by twinning and the following change in the crystal symmetry: cubic paired left right arrows tetragonal paired left right arrows monoclinic. Optical second harmonic generation is found to occur at room temperature, which indicates that the cubic phase is not centrosymmetric. It is assumed that the phase transitions are ferroelastic and ferroelectric in nature.
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