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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Zabluda V. N.
Заглавие : The energy band structure and optical spectra of FeBO3 calculated with allowance for strong electron correlations
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 2004. - Vol. 98, Is. 1. - P135-143. - ISSN 1063-7761, DOI 10.1134/1.1648107
Примечания : Cited References: 32. - This study was supported by the Russian Foundation for Basic Research (project no. 03-02-16286) and by the “Strongly Correlated Electrons” Program of the Department of Physical Sciences of the Russian Academy of Sciences
Предметные рубрики: PHASE-TRANSITION
HIGH-PRESSURE
FERROMAGNETISM
MODEL
Ключевые слова (''Своб.индексиров.''): atomic physics--band structure--charge transfer--excitons--green's function--light absorption--dielectric gap--energy band structure--lehmann spectral representation--optical spectra--iron compounds
Аннотация: A model of the energy band structure of iron borate (FeBO3) is proposed that combines a one-electron description of the sp states of boron and oxygen with a many-electron description of the d states of iron. The Green functions of d electrons are calculated using the exact Lehmann spectral representation. The energies of the d-type quasiparticles are calculated using terms of the d(4) , d(5) , and d(6) electron configurations. The optical absorption spectrum of FeBO3 is determined by local excitons and by the electron excitations with charge transfer. The latter excitations control the nature of the dielectric gap in FeBO3 crystals. The model parameters are determined from a comparison to the exciton energies. The density of single-particle states in FeBO3 is calculated. The main bands in the calculated optical absorption spectrum agree well with experimental data for energies up to 3 eV. (C) 2004 MAIK "Nauka/Interperiodica".
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Dzebisashvili D. M.
Заглавие : Spin-Fluctuation Renormalization of the Temperature of a Superconducting s-Phase in Rare-Earth Intermetallides
Коллективы :
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2008. - Vol. 107, Is. 4. - P679-691. - ISSN 1063-7761, DOI 10.1134/S1063776108100166
Примечания : Cited References: 34. - This study was supported in part by the Russian Foundation for Basic Research ( project no. 07-02-00226), the Department of Physic of the Russian Academy of Sciences ( within the program "Strongly Correlated Electrons in Semiconductors, Superconductors, and Magnetic Materials"), and the Siberian Branch of the Russian Academy of Sciences ( integration project no. 3.4).
Предметные рубрики: HEAVY-FERMION SUPERCONDUCTORS
PERIODIC ANDERSON MODEL
WAVE SUPERCONDUCTIVITY
PERTURBATION-THEORY
MECHANISM
VALENCE
SYSTEMS
LATTICE
STATE
Ключевые слова (''Своб.индексиров.''): differential equations--electric conductivity--green's function--numerical analysis--rare earth elements--spin dynamics--spin fluctuations--anomalous components--critical temperatures--experimental datums--infinite systems--numerical calculations--order parameters--periodic anderson models--renormalization--s-phase--skutterudite--strong electron correlations--sub systems--superconducting states--superconductivity
Аннотация: A theory of the superconducting state with s-type symmetry of the order parameter ( the transition to this state was observed in recently discovered heavy-fermion skutterudite LaFe(4)P(12)) is developed using the periodic Anderson model in the limit of strong electron correlations. Exact representations of Green's functions of the superconducting phase via the normal and anomalous components of the mass and strength operators are obtained. It is shown that an important role in the description of this superconducting phase is played by the anomalous components of the strength operator, which reflect spin-fluctuation processes in the localized subsystem. These components are calculated in the one-loop approximation using the solution of an infinite system of integral equations of self-consistency for the superconducting phase. Numerical calculations show that allowance for the process of scattering on spin fluctuations leads to renormalization of the critical temperature and provides agreement with the experimental data.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ignatchenko V. A., Mankov Y. I., Tsikalov D. S.
Заглавие : High-Frequency Susceptibility of a Superlattice with 2D Inhomogeneities
Коллективы :
Разночтения заглавия :авие SCOPUS: High-frequency susceptibility of a superlattice with 2D inhomogeneities
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2008. - Vol. 107, Is. 4. - P603-611. - ISSN 1063-7761, DOI 10.1134/S1063776108100075
Примечания : Cited References: 26. - This work was supported in part by grant no. 3818.2008.3 from the President of Russia in accordance with the program supporting leading scientific schools.
Предметные рубрики: SPIN-WAVE SUSCEPTIBILITY
PERIODIC MULTILAYERS
LOCALIZATION
SYSTEMS
SPECTRUM
DISORDER
MEDIA
Ключевые слова (''Своб.индексиров.''): energy conservation--energy gap--energy management--frequency bands--gallium alloys--green's function--probability density function--three dimensional--band gaps--energy conservation laws--green functions--high frequencies--imaginary parts--magnon crystals--scattered waves--superlattice layers--wave spectrums--phase interfaces
Аннотация: We investigate the high-frequency susceptibility (Green function) of an initially sinusoidal 1D superlattice with 2D phase inhomogeneities that model the deformations of the interfaces between the superlattice layers. For waves propagating along the superlattice axis ( the geometry of a photon or magnon crystal), we have found a peculiar behavior of the imaginary part of the Green function that consists in a significant difference between the peaks corresponding to the edges of the band gap in the wave spectrum. The peak corresponding to the lower-frequency band edge remains essentially unchanged as the root-mean-square fluctuation of the 2D inhomogeneities. 2 increases, while the peak corresponding to the higher-frequency band edge broaden and decreases sharply in height until its complete disappearance with increasing gamma(2). This behavior of the peaks corresponds to a band gap closure mechanism that differs from the traditional one characteristic of 1D and 3D inhomogeneities. These effects can be explained by a peculiarity of the energy conservation laws for the incident and scattered waves for 2D inhomogeneities in a 1D superlattice.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kuz'min E. V.
Заглавие : Quantum spin liquid in the FCC lattice
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 2003. - Vol. 96, Is. 1. - P129-139. - ISSN 1063-7761, DOI 10.1134/1.1545392
Примечания : Cited References: 12
Предметные рубрики: HEISENBERG-ANTIFERROMAGNET
TRANSITION
Ключевые слова (''Своб.индексиров.''): antiferromagnetism--green's function--linear systems--magnetic couplings--quantum theory--thermodynamic properties--antiferromagnetic interactions--green temperature functions--heisenberg model--quantum spin liquid--spin system--spin-wave theory--crystal lattices
Аннотация: The properties of the spin system in the FCC lattice described by the Heisenberg model (s=1/2) with antiferromagnetic interactions between the nearest neighbors were studied. It was shown within the framework of spin-wave theory that long-range antiferromagnetic order was absent because of frustration of exchange coupling and transverse quantum spin fluctuations. The system was in the quantum spin liquid state. A method for describing it within linear second-order theory with self-consistently calculated parameters was suggested. It was proved that the ground spin liquid state was singlet. The thermodynamic properties of the spin liquid in the whole temperature range and the character of spatial spin correlations, which had alternating signs and a finite correlation length, were determined. The theory was constructed based on the method of two-time Green temperature functions. (C) 2003 MAIK "Nauka/Interperiodica".
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Dzebisashvili D. M.
Заглавие : Spin fluctuation processes in the problem of s-wave superconducting phase of the heavy-fermion intermetallides
Место публикации : J. Phys. Conf. Ser. - 2010. - Vol. 200, Is. SECTION 1. - ISSN 17426588 (ISSN), DOI 10.1088/1742-6596/200/1/012030
Ключевые слова (''Своб.индексиров.''): anomalous component--critical points--critical temperatures--heavy-fermion--hubbard operators--kinematic mechanism--one-loop approximation--periodic anderson model--self-consistent equations--skutterudites--strong electron correlations--superconducting phase--superconducting phase transitions--green's function--mathematical operators--phase diagrams--shear waves--spin fluctuations--superconductivity--phase transitions
Аннотация: In the framework of the periodic Anderson model in the limit of strong electron correlations a theory of s-wave superconductivity (this phase has been recently discovered in the skutterudite LaFe4P12) has been developed. The theory is based on kinematic mechanism, provided that the spin fluctuation processes (SFP) are taken into account.To obtain the self-consistent equations for the superconducting phase the diagram technique for Hubbard operators has been used. The exact representations of normal and anomalous Green's functions in terms of normal and anomalous components of mass and strength operators have been obtained. A set of integral equations for superconducting phase was deduced with the assumption that SFP have been accounted for. In the solution of these equations normal and anomalous components of the mass and strength operators have been calculated in the one-loop approximation. Computation has revealed that SFP result in substantial decreasing of critical temperature Tc and shifting the concentration critical point of the superconducting phase transition. © 2010 IOP Publishing Ltd.
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Вид документа : Статья из сборника (выпуск продолж. издания)
Шифр издания :
Автор(ы) : Ignatchenko V. A., Tsikalov D. S.
Заглавие : Local density of states in one-dimensional photonic crystals and sinusoidal superlattices
Коллективы : International Conference on Photonics of Nano- and Bio-Structures, International Conference on Photonics of Nano- and Micro-Structures
Место публикации : Physics Procedia: Elsevier, 2017. - Vol. 86. - P.113-116. - , DOI 10.1016/j.phpro.2017.01.030
Примечания : Cited References: 14
Ключевые слова (''Своб.индексиров.''): photonic crystals--green's function--ldos--sinusoidal modulation--chain fractions
Аннотация: We have calculated the local density of states (LDOS) for four Brillouin zones of a superlattice for a plane source depending on its location relative to the change in the profile of dielectricpermeability (z) of the superlattice. It is shown that the LDOS for the cases of sinusoidal and rectangular profiles of (z) are close to each other in the first and second Brillouin zones, and sharp differences between them appear beginning with the third zone. Radical changes in the LDOS occur in a rectangular superlattice with different thicknesses of adjacent layers. In this case, the function LDOS has a sharp jump at the edges of the allowed bands in the transition from one layer to another. The effects studied theoretically in this paper, can be detected and studied experimentally by the intensively developing currently methods of nanooptics. © 2017 The Authors.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Fransson J., Eriksson O., Johansson B., Sandalov I. S.
Заглавие : On the non-orthogonality problem in the description of quantum devices
Коллективы : International Conference on Nonequilibrium Carrier Dynamics in Semiconductors
Место публикации : Physica B/ International Conference on Nonequilibrium Carrier Dynamics in Semiconductors (11 ; 1999 ; July ; 19-23 ; Kyoto, Japan). - 1999. - Vol. 272, Is. 1-4. - P.28-30. - ISSN 0921-4526, DOI 10.1016/S0921-4526(99)00343-9
Примечания : Cited References: 8
Предметные рубрики:
Ключевые слова (''Своб.индексиров.''): non-orthogonality--current--tunneling--correlation methods--electric contacts--electric currents--electron energy levels--electron tunneling--equations of motion--green's function--mathematical operators--matrix algebra--hubbard operators--potential barriers--tunneling currents--semiconductor quantum dots
Аннотация: An approach which allows to include the corrections from non-orthogonality of electron states in contacts and quantum dots is developed. Comparison of the energy levels and charge distributions of electrons in 1D quantum dot (QD) in equilibrium, obtained within orthogonal (OR) and non-orthogonal representations (NOR), with the exact ones shows that the NOR provides a considerable improvement, for levels below the top of barrier. The approach is extended to non-equilibrium states. A derivation of the tunneling current through a single potential barrier is performed using equations of motion for correlation functions. A formula for transient current derived by means of the diagram technique for Hubbard operators is given for the problem of QD with strongly correlated electrons interacting with electrons in contacts. The non-orthogonality renormalizes the tunneling matrix elements and spectral weights of Green functions. (C) 1999 Elsevier Science B.V. All rights reserved.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Fedoseev A. D.
Заглавие : Thermodynamic properties of two-layer quasi-two-dimensional antiferromagnets
Место публикации : Theor. Math. Phys.: SPRINGER, 2011. - Vol. 168, Is. 3. - P1216-1224. - ISSN 0040-5779, DOI 10.1007/s11232-011-0099-6
Примечания : Cited References: 16. - This work was supported in part by the Russian Foundation for Basic Research (Grant No. 10-02-00251), the Presidium of the Russian Academy of Sciences (Fundamental Research Program "Quantum Physics of Condensed Matter"), the Siberian Branch of the Russian Academy of Sciences (Integration Project No. 53 and Lavrentiev Competition of Youth Projects, A. D. F.), the Ministry of Education and Science of the Russian Federation (Program "Scientific and Pedagogical Personnel of Innovative Russia" for 2009-2013), and the President of the Russian Federation (Grant No. MK-1300.2011.2, A. D. F.).
Предметные рубрики: HEISENBERG-MODEL
SPIN-WAVE
Ключевые слова (''Своб.индексиров.''): antiferromagnetism--high-temperature superconductor--tyablikov approximation--green's function--antiferromagnetism--green's function--high-temperature superconductor--tyablikov approximation
Аннотация: For two-layer quasi-two-dimensional antiferromagnets of type YBaCuO in the Tyablikov approximation, we investigate the dependences of the energy spectrum and the temperature of transition into an ordered state on both the quasi-two-dimensionality parameter and the intensity of the exchange coupling of spin moments located in two close planes. We assume that the exchange parameters inside the CuO (2) planes are much greater than the exchange parameters resulting in coupling between a spin located on a plane of an elementary cell and a spin on another plane of a different elementary cell. The obtained expressions for the N,el temperature and for the sublattice magnetic moment at zero temperature describe the dependences of these quantities on the parameters of interplane exchange interactions.
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Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Ignatchenko V. A., Pozdnyakov A. V.
Заглавие : Spectral Properties of Superlattices with Anisotropic inhomogeneities. The Transition from 3D to 1D Disorder
Коллективы : Euro-Asian Symposium "Trends in MAGnetism", "Trends in MAGnetism", Euro-Asian Symposium
Место публикации : TRENDS IN MAGNETISM. Ser. Solid State Phenomena/ Euro-Asian Symposium "Trends in MAGnetism": Nanospintronics (4 ; 2010 ; 28 June-2 July ; Ekaterinburg): TRANS TECH PUBLICATIONS LTD, 2011. - Vol. 168-169. - P.85-88. - ISBN 1012-0394, DOI 10.4028/www.scientific.net/SSP.168-169.85
Примечания : Cited References: 4
Ключевые слова (''Своб.индексиров.''): superlattice--waves--anisotropic inhomogeneities--green's function--susceptibility--dos
Аннотация: Waves in the superlattice (SL) contained inhomogeneities with anisotropic correlation properties are considered. The anisotropy of the correlations is characterized by the parameter lambda=1-k(perpendicular to)/k(parallel to), where k(parallel to) and k(perpendicular to) are the correlation wave numbers along the axis of the SL and in the plane of its layers, respectively (r(parallel to) = k(parallel to)(-1) and r(perpendicular to) = k(perpendicular to)(-1) are the correlation radii). Dependencies of both the dynamic susceptibility and density of states at the continuous transition from the isotropic three-dimensional inhomogeneities (lambda=0) to the one-dimensional ones (lambda=1) have been obtained.
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10.

Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Ignatchenko V. A., Pozdnyakov A. V.
Заглавие : Spectral properties of superlattices with anisotropic inhomogeneities. The transition from 3D to 2D disorder
Коллективы : Moscow International Symposium on Magnetism
Место публикации : Diffusion and Defect Data Pt.B: Solid State Phenomena. - 2012. - Vol. 190. - P.597-600. - ISBN 1012-0394, DOI 10.4028/www.scientific.net/SSP.190.597. - ISBN 9783037854365
Ключевые слова (''Своб.индексиров.''): anisotropic inhomogeneities--dos--green function--superlattice--susceptibility--waves--anisotropic inhomogeneities--continuous transitions--correlation properties--density of state--dynamic susceptibility--inhomogeneities--spectral properties--wave numbers--dos--green's function--magnetic materials--magnetic susceptibility--superlattices--three dimensional--waves--anisotropy
Аннотация: Waves in superlattice (SL) contained inhomogeneities with anisotropic correlation properties are considered. The anisotropy of the correlation during the transition from 3D to 2D disorder is characterized by the parameter ? 1 = k ||/k?-1, where k || and k? are the correlation wave numbers along the axis of the SL and in the plane of the its layers, respectively (r || =k || -1 and r?=k?-1 are the correlation radii). Dependencies of both the dynamic susceptibility and density of states at the continuous transition from the isotropic three-dimensional inhomogeneities (? 1 = 0) to the twodimensional ones (? 1 = -1) have been obtained. В© (2012) Trans Tech Publications.
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